Features
•High-performance, Low-power AVR® 8-bit Microcontroller
•Advanced RISC Architecture
– 131 Powerful Instructions – Most Single-clock Cycle Execution
– 32 x 8 General Purpose Working Registers
– Fully Static Operation
– Up to 16 MIPS Throughput at 16 MHz
– On-chip 2-cycle Multiplier
•High Endurance Non-volatile Memory segments
– 16K Bytes of In-System Self-programmable Flash program memory
– 512 Bytes EEPROM
– 1K Bytes Internal SRAM
– Write/Erase cycles: 10,000 Flash/100,000 EEPROM
– Data retention: 20 years at 85°C/100 years at 25°C(1)
– Optional Boot Code Section with Independent Lock Bits
In-System Programming by On-chip Boot Program
True Read-While-Write Operation
– Up to 64K Bytes Optional External Memory Space
– Programming Lock for Software Security
•JTAG (IEEE std. 1149.1 Compliant) Interface
– Boundary-scan Capabilities According to the JTAG Standard
– Extensive On-chip Debug Support
– Programming of Flash, EEPROM, Fuses, and Lock Bits through the JTAG Interface
•Peripheral Features
– Two 8-bit Timer/Counters with Separate Prescalers and Compare Modes
– Two 16-bit Timer/Counters with Separate Prescalers, Compare Modes, and
Capture Modes
– Real Time Counter with Separate Oscillator
– Six PWM Channels
– Dual Programmable Serial USARTs
– Master/Slave SPI Serial Interface
– Programmable Watchdog Timer with Separate On-chip Oscillator
– On-chip Analog Comparator
•Special Microcontroller Features
– Power-on Reset and Programmable Brown-out Detection
– Internal Calibrated RC Oscillator
– External and Internal Interrupt Sources
– Five Sleep Modes: Idle, Power-save, Power-down, Standby, and Extended Standby
•I/O and Packages
– 35 Programmable I/O Lines
– 40-pin PDIP, 44-lead TQFP, and 44-pad MLF
•Operating Voltages
– 1.8 - 5.5V for ATmega162V
– 2.7 - 5.5V for ATmega162
•Speed Grades
– 0 - 8 MHz for ATmega162V (see Figure 113 on page 266)
– 0 - 16 MHz for ATmega162 (see Figure 114 on page 266)
8-bit
Microcontroller
with 16K Bytes
In-System
Programmable
Flash
ATmega162
ATmega162V
2513K–AVR–07/09
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ATmega162/V
Pin
Configurations
Figure 1. Pinout ATmega162
Disclaimer Typical values contained in this datasheet are based on simulations and characterization of
other AVR microcontrollers manufactured on the same process technology. Min and Max values
will be available after the device is characterized.
(OC0/T0) PB0
(OC2/T1) PB1
(RXD1/AIN0) PB2
(TXD1/AIN1) PB3
(SS/OC3B) PB4
(MOSI) PB5
(MISO) PB6
(SCK) PB7
RESET
(RXD0) PD0
(TXD0) PD1
(INT0/XCK1) PD2
(INT1/ICP3) PD3
(TOSC1/XCK0/OC3A) PD4
(OC1A/TOSC2) PD5
(WR) PD6
(RD) PD7
XTAL2
XTAL1
GND
VCC
PA0 (AD0/PCINT0)
PA1 (AD1/PCINT1)
PA2 (AD2/PCINT2)
PA3 (AD3/PCINT3)
PA4 (AD4/PCINT4)
PA5 (AD5/PCINT5)
PA6 (AD6/PCINT6)
PA7 (AD7/PCINT7)
PE0 (ICP1/INT2)
PE1 (ALE)
PE2 (OC1B)
PC7 (A15/TDI/PCINT15)
PC6 (A14/TDO/PCINT14)
PC5 (A13/TMS/PCINT13)
PC4 (A12/TCK/PCINT12)
PC3 (A11/PCINT11)
PC2 (A10/PCINT10)
PC1 (A9/PCINT9)
PC0 (A8/PCINT8)
PA4 (AD4/PCINT4)
PA5 (AD5/PCINT5)
PA6 (AD6/PCINT6)
PA7 (AD7/PCINT7)
PE0 (ICP1/INT2)
GND
PE1 (ALE)
PE2 (OC1B)
PC7 (A15/TDI/PCINT15)
PC6 (A14/TDO/PCINT14)
PC5 (A13/TMS/PCINT13)
(MOSI) PB5
(MISO) PB6
(SCK) PB7
RESET
(RXD0) PD0
VCC
(TXD0) PD1
(INT0/XCK1) PD2
(INT1/ICP3) PD3
(TOSC1/XCK0/OC3A) PD4
(OC1A/TOSC2) PD5
(WR) PD6
(RD) PD7
XTAL2
XTAL1
GND
VCC
(A8/PCINT8) PC0
(A9/PCINT9) PC1
(A10/PCINT10) PC2
(A11/PCINT11) PC3
(TCK/A12/PCINT12) PC4
PB4 (SS/OC3B)
PB3 (TXD1/AIN1)
PB2 (RXD1/AIN0)
PB1 (OC2/T1)
PB0 (OC0/T0)
GND
VCC
PA0 (AD0/PCINT0)
PA1 (AD1/PCINT1)
PA2 (AD2/PCINT2)
PA3 (AD3/PCINT3)
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
PDIP
1
2
3
4
5
6
7
8
9
10
11
12 14 16 18 20 22
13 15 17 19 21
33
32
31
30
29
28
27
26
25
24
23
44 42 40 38 36 34
43 41 39 37 35
TQFP/MLF
NOTE:
MLF bottom pad should
be soldered to ground.
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ATmega162/V
Overview The ATmega162 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced RISC
architecture. By executing powerful instructions in a single clock cycle, the ATmega162
achieves throughputs approaching 1 MIPS per MHz allowing the system designer to optimize
power consumption versus processing speed.
Block Diagram Figure 2. Block Diagram
INTERNAL
OSCILLATOR
OSCILLATOR
WATCHDOG
TIMER
MCU CTRL.
& TIMING
OSCILLATOR
TIMERS/
COUNTERS
INTERRUPT
UNIT
STACK
POINTER
EEPROM
SRAM
STATUS
REGISTER
USART0
PROGRAM
COUNTER
PROGRAM
FLASH
INSTRUCTION
REGISTER
INSTRUCTION
DECODER
PROGRAMMING
LOGIC
SPI
COMP.
INTERFACE
PORTA DRIVERS/BUFFERS
PORTA DIGITAL INTERFACE
GENERAL
PURPOSE
REGISTERS
X
Y
Z
ALU
+
-
PORTC DRIVERS/BUFFERS
PORTC DIGITAL INTERFACE
PORTB DIGITAL INTERFACE
PORTB DRIVERS/BUFFERS
PORTD DIGITAL INTERFACE
PORTD DRIVERS/BUFFERS
XTAL1
XTAL2
RESET
CONTROL
LINES
VCC
GND
PA0 - PA7 PC0 - PC7
PD0 - PD7PB0 - PB7
AVR CPU
INTERNAL
CALIBRATED
OSCILLATOR
PORTE
DRIVERS/
BUFFERS
PORTE
DIGITAL
INTERFACE
PE0 - PE2
USART1
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ATmega162/V
The AVR core combines a rich instruction set with 32 general purpose working registers. All the
32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two independent
registers to be accessed in one single instruction executed in one clock cycle. The resulting
architecture is more code efficient while achieving throughputs up to ten times faster than con-
ventional CISC microcontrollers.
The ATmega162 provides the following features: 16K bytes of In-System Programmable Flash
with Read-While-Write capabilities, 512 bytes EEPROM, 1K bytes SRAM, an external memory
interface, 35 general purpose I/O lines, 32 general purpose working registers, a JTAG interface
for Boundary-scan, On-chip Debugging support and programming, four flexible Timer/Counters
with compare modes, internal and external interrupts, two serial programmable USARTs, a pro-
grammable Watchdog Timer with Internal Oscillator, an SPI serial port, and five software
selectable power saving modes. The Idle mode stops the CPU while allowing the SRAM,
Timer/Counters, SPI port, and interrupt system to continue functioning. The Power-down mode
saves the register contents but freezes the Oscillator, disabling all other chip functions until the
next interrupt or Hardware Reset. In Power-save mode, the Asynchronous Timer continues to
run, allowing the user to maintain a timer base while the rest of the device is sleeping. In
Standby mode, the crystal/resonator Oscillator is running while the rest of the device is sleeping.
This allows very fast start-up combined with low-power consumption. In Extended Standby
mode, both the main Oscillator and the Asynchronous Timer continue to run.
The device is manufactured using Atmel’s high density non-volatile memory technology. The
On-chip ISP Flash allows the program memory to be reprogrammed In-System through an SPI
serial interface, by a conventional non-volatile memory programmer, or by an On-chip Boot Pro-
gram running on the AVR core. The Boot Program can use any interface to download the
Application Program in the Application Flash memory. Software in the Boot Flash section will
continue to run while the Application Flash section is updated, providing true Read-While-Write
operation. By combining an 8-bit RISC CPU with In-System Self-Programmable Flash on a
monolithic chip, the Atmel ATmega162 is a powerful microcontroller that provides a highly flexi-
ble and cost effective solution to many embedded control applications.
The ATmega162 AVR is supported with a full suite of program and system development tools
including: C compilers, macro assemblers, program debugger/simulators, In-Circuit Emulators,
and evaluation kits.
ATmega161 and
ATmega162
Compatibility
The ATmega162 is a highly complex microcontroller where the number of I/O locations super-
sedes the 64 I/O locations reserved in the AVR instruction set. To ensure back-ward
compatibility with the ATmega161, all I/O locations present in ATmega161 have the same loca-
tions in ATmega162. Some additional I/O locations are added in an Extended I/O space starting
from 0x60 to 0xFF, (i.e., in the ATmega162 internal RAM space). These locations can be
reached by using LD/LDS/LDD and ST/STS/STD instructions only, not by using IN and OUT
instructions. The relocation of the internal RAM space may still be a problem for ATmega161
users. Also, the increased number of Interrupt Vectors might be a problem if the code uses
absolute addresses. To solve these problems, an ATmega161 compatibility mode can be
selected by programming the fuse M161C. In this mode, none of the functions in the Extended
I/O space are in use, so the internal RAM is located as in ATmega161. Also, the Extended Inter-
rupt Vec-tors are removed. The ATmega162 is 100% pin compatible with ATmega161, and can
replace the ATmega161 on current Printed Circuit Boards. However, the location of Fuse bits
and the electrical characteristics differs between the two devices.
ATmega161
Compatibility Mode
Programming the M161C will change the following functionality:
• The extended I/O map will be configured as internal RAM once the M161C Fuse is
programmed.
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2513K–AVR–07/09
ATmega162/V
• The timed sequence for changing the Watchdog Time-out period is disabled. See “Timed
Sequences for Changing the Configuration of the Watchdog Timer” on page 56 for details.
• The double buffering of the USART Receive Registers is disabled. See “AVR USART vs.
AVR UART – Compatibility” on page 168 for details.
• Pin change interrupts are not supported (Control Registers are located in Extended I/O).
• One 16 bits Timer/Counter (Timer/Counter1) only. Timer/Counter3 is not accessible.
Note that the shared UBRRHI Register in ATmega161 is split into two separate registers in
ATmega162, UBRR0H and UBRR1H. The location of these registers will not be affected by the
ATmega161 compatibility fuse.
Pin Descriptions
VCC Digital supply voltage
GND Ground
Port A (PA7..PA0) Port A is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port A output buffers have symmetrical drive characteristics with both high sink and source
capability. When pins PA0 to PA7 are used as inputs and are externally pulled low, they will
source current if the internal pull-up resistors are activated. The Port A pins are tri-stated when a
reset condition becomes active, even if the clock is not running.
Port A also serves the functions of various special features of the ATmega162 as listed on page
72.
Port B (PB7..PB0) Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port B output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port B pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port B pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port B also serves the functions of various special features of the ATmega162 as listed on page
72.
Port C (PC7..PC0) Port C is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port C output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port C pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port C pins are tri-stated when a reset condition becomes active,
even if the clock is not running. If the JTAG interface is enabled, the pull-up resistors on pins
PC7(TDI), PC5(TMS) and PC4(TCK) will be activated even if a Reset occurs.
Port C also serves the functions of the JTAG interface and other special features of the
ATmega162 as listed on page 75.
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Port D (PD7..PD0) Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port D output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port D pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port D pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port D also serves the functions of various special features of the ATmega162 as listed on page
78.
Port E(PE2..PE0) Port E is an 3-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port E output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port E pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port E pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port E also serves the functions of various special features of the ATmega162 as listed on page
81.
RESET Reset input. A low level on this pin for longer than the minimum pulse length will generate a
Reset, even if the clock is not running. The minimum pulse length is given in Table 18 on page
48. Shorter pulses are not guaranteed to generate a reset.
XTAL1 Input to the Inverting Oscillator amplifier and input to the internal clock operating circuit.
XTAL2 Output from the Inverting Oscillator amplifier.
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2513K–AVR–07/09
ATmega162/V
Resources A comprehensive set of development tools, application notes and datasheets are available for
download on http://www.atmel.com/avr.
Note: 1.
Data Retention Reliability Qualification results show that the projected data retention failure rate is much less
than 1 PPM over 20 years at 85°C or 100 years at 25°C.
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2513K–AVR–07/09
ATmega162/V
About Code
Examples
This documentation contains simple code examples that briefly show how to use various parts of
the device. These code examples assume that the part specific header file is included before
compilation. Be aware that not all C compiler vendors include bit definitions in the header files
and interrupt handling in C is compiler dependent. Please confirm with the C compiler documen-
tation for more details.
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ATmega162/V
AVR CPU Core
Introduction This section discusses the AVR core architecture in general. The main function of the CPU core
is to ensure correct program execution. The CPU must therefore be able to access memories,
perform calculations, control peripherals, and handle interrupts.
Architectural
Overview
Figure 3. Block Diagram of the AVR Architecture
In order to maximize performance and parallelism, the AVR uses a Harvard architecture – with
separate memories and buses for program and data. Instructions in the program memory are
executed with a single level pipelining. While one instruction is being executed, the next instruc-
tion is pre-fetched from the program memory. This concept enables instructions to be executed
in every clock cycle. The program memory is In-System Reprogrammable Flash memory.
The fast-access Register File contains 32 x 8-bit general purpose working registers with a single
clock cycle access time. This allows single-cycle Arithmetic Logic Unit (ALU) operation. In a typ-
ical ALU operation, two operands are output from the Register File, the operation is executed,
and the result is stored back in the Register File – in one clock cycle.
Six of the 32 registers can be used as three 16-bit indirect address register pointers for Data
Space addressing – enabling efficient address calculations. One of the these address pointers
Flash
Program
Memory
Instruction
Register
Instruction
Decoder
Program
Counter
Control Lines
32 x 8
General
Purpose
Registrers
ALU
Status
and Control
I/O Lines
EEPROM
Data Bus 8-bit
Data
SRAM
Direct Addressing
Indirect Addressing
Interrupt
Unit
SPI
Unit
Watchdog
Timer
Analog
Comparator
I/O Module 2
I/O Module1
I/O Module n
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ATmega162/V
can also be used as an address pointer for look up tables in Flash Program memory. These
added function registers are the 16-bit X-, Y-, and Z-register, described later in this section.
The ALU supports arithmetic and logic operations between registers or between a constant and
a register. Single register operations can also be executed in the ALU. After an arithmetic opera-
tion, the Status Register is updated to reflect information about the result of the operation.
Program flow is provided by conditional and unconditional jump and call instructions, able to
directly address the whole address space. Most AVR instructions have a single 16-bit word for-
mat. Every program memory address contains a 16- or 32-bit instruction.
Program Flash memory space is divided in two sections, the Boot Program section and the
Application Program section. Both sections have dedicated Lock bits for write and read/write
protection. The SPM instruction that writes into the Application Flash memory section must
reside in the Boot Program section.
During interrupts and subroutine calls, the return address Program Counter (PC) is stored on the
Stack. The Stack is effectively allocated in the general data SRAM, and consequently the Stack
size is only limited by the total SRAM size and the usage of the SRAM. All user programs must
initialize the SP in the reset routine (before subroutines or interrupts are executed). The Stack
Pointer SP is read/write accessible in the I/O space. The data SRAM can easily be accessed
through the five different addressing modes supported in the AVR architecture.
The memory spaces in the AVR architecture are all linear and regular memory maps.
A flexible interrupt module has its control registers in the I/O space with an additional Global
Interrupt Enable bit in the Status Register. All interrupts have a separate Interrupt Vector in the
Interrupt Vector table. The interrupts have priority in accordance with their Interrupt Vector posi-
tion. The lower the Interrupt Vector address, the higher the priority.
The I/O memory space contains 64 addresses for CPU peripheral functions as Control Regis-
ters, SPI, and other I/O functions. The I/O memory can be accessed directly, or as the Data
Space locations following those of the Register File, 0x20 - 0x5F.
ALU – Arithmetic
Logic Unit
The high-performance AVR ALU operates in direct connection with all the 32 general purpose
working registers. Within a single clock cycle, arithmetic operations between general purpose
registers or between a register and an immediate are executed. The ALU operations are divided
into three main categories – arithmetic, logical, and bit-functions. Some implementations of the
architecture also provide a powerful multiplier supporting both signed/unsigned multiplication
and fractional format. See the “Instruction Set” section for a detailed description.
Status Register The Status Register contains information about the result of the most recently executed arithme-
tic instruction. This information can be used for altering program flow in order to perform
conditional operations. Note that the Status Register is updated after all ALU operations, as
specified in the Instruction Set Reference. This will in many cases remove the need for using the
dedicated compare instructions, resulting in faster and more compact code.
The Status Register is not automatically stored when entering an interrupt routine and restored
when returning from an interrupt. This must be handled by software.
The AVR Status Register – SREG – is defined as:
Bit 76543210
I T H S V N Z C SREG
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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• Bit 7 – I: Global Interrupt Enable
The Global Interrupt Enable bit must be set for the interrupts to be enabled. The individual inter-
rupt enable control is then performed in separate control registers. If the Global Interrupt Enable
Register is cleared, none of the interrupts are enabled independent of the individual interrupt
enable settings. The I-bit is cleared by hardware after an interrupt has occurred, and is set by
the RETI instruction to enable subsequent interrupts. The I-bit can also be set and cleared by
the application with the SEI and CLI instructions, as described in the instruction set reference.
• Bit 6 – T: Bit Copy Storage
The Bit Copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T bit as source or destina-
tion for the operated bit. A bit from a register in the Register File can be copied into T by the BST
instruction, and a bit in T can be copied into a bit in a register in the Register File by the BLD
instruction.
• Bit 5 – H: Half Carry Flag
The Half Carry Flag H indicates a half carry in some arithmetic operations. Half Carry is useful in
BCD arithmetic. See the “Instruction Set Description” for detailed information.
• Bit 4 – S: Sign Bit, S = N ⊕ V
The S-bit is always an exclusive or between the Negative Flag N and the Two’s Complement
Overflow Flag V. See the “Instruction Set Description” for detailed information.
• Bit 3 – V: Two’s Complement Overflow Flag
The Two’s Complement Overflow Flag V supports two’s complement arithmetics. See the
“Instruction Set Description” for detailed information.
• Bit 2 – N: Negative Flag
The Negative Flag N indicates a negative result in an arithmetic or logic operation. See the
“Instruction Set Description” for detailed information.
• Bit 1 – Z: Zero Flag
The Zero Flag Z indicates a zero result in an arithmetic or logic operation. See the “Instruction
Set Description” for detailed information.
• Bit 0 – C: Carry Flag
The Carry Flag C indicates a carry in an arithmetic or logic operation. See the “Instruction Set
Description” for detailed information.
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General Purpose
Register File
The Register File is optimized for the AVR Enhanced RISC instruction set. In order to achieve
the required performance and flexibility, the following input/output schemes are supported by the
Register File:
• One 8-bit output operand and one 8-bit result input
• Two 8-bit output operands and one 8-bit result input
• Two 8-bit output operands and one 16-bit result input
• One 16-bit output operand and one 16-bit result input
Figure 4 shows the structure of the 32 general purpose working registers in the CPU.
Figure 4. AVR CPU General Purpose Working Registers
Most of the instructions operating on the Register File have direct access to all registers, and
most of them are single cycle instructions.
As shown in Figure 4, each register is also assigned a data memory address, mapping them
directly into the first 32 locations of the user Data Space. Although not being physically imple-
mented as SRAM locations, this memory organization provides great flexibility in access of the
registers, as the X-, Y-, and Z-pointer registers can be set to index any register in the file.
7 0 Addr.
R0 0x00
R1 0x01
R2 0x02
…
R13 0x0D
General R14 0x0E
Purpose R15 0x0F
Working R16 0x10
Registers R17 0x11
…
R26 0x1A X-register Low Byte
R27 0x1B X-register High Byte
R28 0x1C Y-register Low Byte
R29 0x1D Y-register High Byte
R30 0x1E Z-register Low Byte
R31 0x1F Z-register High Byte
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ATmega162/V
The X-register, Y-
register, and Z-register
The registers R26..R31 have some added functions to their general purpose usage. These reg-
isters are 16-bit address pointers for indirect addressing of the Data Space. The three indirect
address registers X, Y, and Z are defined as described in Figure 5.
Figure 5. The X-, Y-, and Z-registers
In the different addressing modes these address registers have functions as fixed displacement,
automatic increment, and automatic decrement (see the instruction set reference for details).
Stack Pointer The Stack is mainly used for storing temporary data, for storing local variables and for storing
return addresses after interrupts and subroutine calls. The Stack Pointer Register always points
to the top of the Stack. Note that the Stack is implemented as growing from higher memory loca-
tions to lower memory locations. This implies that a Stack PUSH command decreases the Stack
Pointer.
The Stack Pointer points to the data SRAM Stack area where the Subroutine and Interrupt
Stacks are located. This Stack space in the data SRAM must be defined by the program before
any subroutine calls are executed or interrupts are enabled. The Stack Pointer must be set to
point above 0x60. The Stack Pointer is decremented by one when data is pushed onto the Stack
with the PUSH instruction, and it is decremented by two when the return address is pushed onto
the Stack with subroutine call or interrupt. The Stack Pointer is incremented by one when data is
popped from the Stack with the POP instruction, and it is incremented by two when data is
popped from the Stack with return from subroutine RET or return from interrupt RETI.
The AVR Stack Pointer is implemented as two 8-bit registers in the I/O space. The number of
bits actually used is implementation dependent. Note that the data space in some implementa-
tions of the AVR architecture is so small that only SPL is needed. In this case, the SPH Register
will not be present.
15 XH XL 0
X - register 7 0 7 0
R27 (0x1B) R26 (0x1A)
15 YH YL 0
Y - register 7 0 7 0
R29 (0x1D) R28 (0x1C)
15 ZH ZL 0
Z - register 7 0 7 0
R31 (0x1F) R30 (0x1E)
Bit 151413121110 9 8
SP15 SP14 SP13 SP12 SP11 SP10 SP9 SP8 SPH
SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 SPL
76543210
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
00000000
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ATmega162/V
Instruction
Execution Timing
This section describes the general access timing concepts for instruction execution. The AVR
CPU is driven by the CPU clock clkCPU, directly generated from the selected clock source for the
chip. No internal clock division is used.
Figure 6 shows the parallel instruction fetches and instruction executions enabled by the Har-
vard architecture and the fast-access Register File concept. This is the basic pipelining concept
to obtain up to 1 MIPS per MHz with the corresponding unique results for functions per cost,
functions per clocks, and functions per power-unit.
Figure 6. The Parallel Instruction Fetches and Instruction Executions
Figure 7 shows the internal timing concept for the Register File. In a single clock cycle an ALU
operation using two register operands is executed, and the result is stored back to the destina-
tion register.
Figure 7. Single Cycle ALU Operation
Reset and
Interrupt Handling
The AVR provides several different interrupt sources. These interrupts and the separate Reset
Vector each have a separate program vector in the program memory space. All interrupts are
assigned individual enable bits which must be written logic one together with the Global Interrupt
Enable bit in the Status Register in order to enable the interrupt. Depending on the Program
Counter value, interrupts may be automatically disabled when Boot Lock bits BLB02 or BLB12
are programmed. This feature improves software security. See the section “Memory Program-
ming” on page 231 for details.
The lowest addresses in the program memory space are by default defined as the Reset and
Interrupt Vectors. The complete list of vectors is shown in “Interrupts” on page 57. The list also
determines the priority levels of the different interrupts. The lower the address the higher is the
priority level. RESET has the highest priority, and next is INT0 – the External Interrupt Request
0. The Interrupt Vectors can be moved to the start of the Boot Flash section by setting the IVSEL
bit in the General Interrupt Control Register (GICR). Refer to “Interrupts” on page 57 for more
information. The Reset Vector can also be moved to the start of the Boot Flash section by pro-
clk
1st Instruction Fetch
1st Instruction Execute
2nd Instruction Fetch
2nd Instruction Execute
3rd Instruction Fetch
3rd Instruction Execute
4th Instruction Fetch
T1 T2 T3 T4
CPU
Total Execution Time
Register Operands Fetch
ALU Operation Execute
Result Write Back
T1 T2 T3 T4
clkCPU
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gramming the BOOTRST Fuse, see “Boot Loader Support – Read-While-Write Self-
programming” on page 217.
When an interrupt occurs, the Global Interrupt Enable I-bit is cleared and all interrupts are dis-
abled. The user software can write logic one to the I-bit to enable nested interrupts. All enabled
interrupts can then interrupt the current interrupt routine. The I-bit is automatically set when a
Return from Interrupt instruction – RETI – is executed.
There are basically two types of interrupts. The first type is triggered by an event that sets the
Interrupt Flag. For these interrupts, the Program Counter is vectored to the actual Interrupt Vec-
tor in order to execute the interrupt handling routine, and hardware clears the corresponding
Interrupt Flag. Interrupt Flags can also be cleared by writing a logic one to the flag bit position(s)
to be cleared. If an interrupt condition occurs while the corresponding interrupt enable bit is
cleared, the Interrupt Flag will be set and remembered until the interrupt is enabled, or the flag is
cleared by software. Similarly, if one or more interrupt conditions occur while the global interrupt
enable bit is cleared, the corresponding Interrupt Flag(s) will be set and remembered until the
Global Interrupt Enable bit is set, and will then be executed by order of priority.
The second type of interrupts will trigger as long as the interrupt condition is present. These
interrupts do not necessarily have Interrupt Flags. If the interrupt condition disappears before the
interrupt is enabled, the interrupt will not be triggered.
When the AVR exits from an interrupt, it will always return to the main program and execute one
more instruction before any pending interrupt is served.
Note that the Status Register is not automatically stored when entering an interrupt routine, nor
restored when returning from an interrupt routine. This must be handled by software.
When using the CLI instruction to disable interrupts, the interrupts will be immediately disabled.
No interrupt will be executed after the CLI instruction, even if it occurs simultaneously with the
CLI instruction. The following example shows how this can be used to avoid interrupts during the
timed EEPROM write sequence.
Assembly Code Example
in r16, SREG ; store SREG value
cli ; disable interrupts during timed sequence
sbi EECR, EEMWE ; start EEPROM write
sbi EECR, EEWE
out SREG, r16 ; restore SREG value (I-bit)
C Code Example
char cSREG;
cSREG = SREG; /* store SREG value */
/* disable interrupts during timed sequence */
_CLI();
EECR |= (1<<EEMWE); /* start EEPROM write */
EECR |= (1<<EEWE);
SREG = cSREG; /* restore SREG value (I-bit) */
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When using the SEI instruction to enable interrupts, the instruction following SEI will be exe-
cuted before any pending interrupts, as shown in this example.
Interrupt Response
Time
The interrupt execution response for all the enabled AVR interrupts is four clock cycles mini-
mum. After four clock cycles the program vector address for the actual interrupt handling routine
is executed. During this four clock cycle period, the Program Counter is pushed onto the Stack.
The vector is normally a jump to the interrupt routine, and this jump takes three clock cycles. If
an interrupt occurs during execution of a multi-cycle instruction, this instruction is completed
before the interrupt is served. If an interrupt occurs when the MCU is in sleep mode, the interrupt
execution response time is increased by four clock cycles. This increase comes in addition to the
start-up time from the selected sleep mode.
A return from an interrupt handling routine takes four clock cycles. During these four clock
cycles, the Program Counter (two bytes) is popped back from the Stack, the Stack Pointer is
incremented by two, and the I-bit in SREG is set.
Assembly Code Example
sei ; set global interrupt enable
sleep ; enter sleep, waiting for interrupt
; note: will enter sleep before any pending
; interrupt(s)
C Code Example
_SEI(); /* set global interrupt enable */
_SLEEP(); /* enter sleep, waiting for interrupt */
/* note: will enter sleep before any pending interrupt(s) */
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AVR
ATmega162
Memories
This section describes the different memories in the ATmega162. The AVR architecture has two
main memory spaces, the Data Memory and the Program Memory space. In addition, the
ATmega162 features an EEPROM Memory for data storage. All three memory spaces are linear
and regular.
In-System
Reprogrammable
Flash Program
Memory
The ATmega162 contains 16K bytes On-chip In-System Reprogrammable Flash memory for
program storage. Since all AVR instructions are 16 or 32 bits wide, the Flash is organized as 8K
x 16. For software security, the Flash Program memory space is divided into two sections, Boot
Program section and Application Program section.
The Flash memory has an endurance of at least 10,000 write/erase cycles. The ATmega162
Program Counter (PC) is 13 bits wide, thus addressing the 8K program memory locations. The
operation of Boot Program section and associated Boot Lock bits for software protection are
described in detail in “Boot Loader Support – Read-While-Write Self-programming” on page 217.
“Memory Programming” on page 231 contains a detailed description on Flash data serial down-
loading using the SPI pins or the JTAG interface.
Constant tables can be allocated within the entire program memory address space (see the LPM
– Load Program Memory instruction description).
Timing diagrams for instruction fetch and execution are presented in “Instruction Execution Tim-
ing” on page 14.
Figure 8. Program Memory Map(1)
Note: 1. The address reflects word addresses.
0x0000
0x1FFF
Program Memory
Application Flash Section
Boot Flash Section
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SRAM Data
Memory
Figure 9 shows how the ATmega162 SRAM Memory is organized. Memory configuration B
refers to the ATmega161 compatibility mode, configuration A to the non-compatible mode.
The ATmega162 is a complex microcontroller with more peripheral units than can be supported
within the 64 location reserved in the Opcode for the IN and OUT instructions. For the Extended
I/O space from 0x60 - 0xFF in SRAM, only the ST/STS/STD and LD/LDS/LDD instructions can
be used. The Extended I/O space does not exist when the ATmega162 is in the ATmega161
compatibility mode.
In Normal mode, the first 1280 Data Memory locations address both the Register File, the I/O
Memory, Extended I/O Memory, and the internal data SRAM. The first 32 locations address the
Register File, the next 64 location the standard I/O memory, then 160 locations of Extended I/O
memory, and the next 1024 locations address the internal data SRAM.
In ATmega161 compatibility mode, the lower 1120 Data Memory locations address the Register
File, the I/O Memory, and the internal data SRAM. The first 96 locations address the Register
File and I/O Memory, and the next 1024 locations address the internal data SRAM.
An optional external data SRAM can be used with the ATmega162. This SRAM will occupy an
area in the remaining address locations in the 64K address space. This area starts at the
address following the internal SRAM. The Register File, I/O, Extended I/O and Internal SRAM
uses the occupies the lowest 1280 bytes in Normal mode, and the lowest 1120 bytes in the
ATmega161 compatibility mode (Extended I/O not present), so when using 64KB (65,536 bytes)
of External Memory, 64,256 Bytes of External Memory are available in Normal mode, and
64,416 Bytes in ATmega161 compatibility mode. See “External Memory Interface” on page 26
for details on how to take advantage of the external memory map.
When the addresses accessing the SRAM memory space exceeds the internal data memory
locations, the external data SRAM is accessed using the same instructions as for the internal
data memory access. When the internal data memories are accessed, the read and write strobe
pins (PD7 and PD6) are inactive during the whole access cycle. External SRAM operation is
enabled by setting the SRE bit in the MCUCR Register.
Accessing external SRAM takes one additional clock cycle per byte compared to access of the
internal SRAM. This means that the commands LD, ST, LDS, STS, LDD, STD, PUSH, and POP
take one additional clock cycle. If the Stack is placed in external SRAM, interrupts, subroutine
calls and returns take three clock cycles extra because the 2-byte Program Counter is pushed
and popped, and external memory access does not take advantage of the internal pipeline
memory access. When external SRAM interface is used with wait-state, one-byte external
access takes two, three, or four additional clock cycles for one, two, and three wait-states
respectively. Interrupt, subroutine calls and returns will need five, seven, or nine clock cycles
more than specified in the instruction set manual for one, two, and three wait-states.
The five different addressing modes for the data memory cover: Direct, Indirect with Displace-
ment, Indirect, Indirect with Pre-decrement, and Indirect with Post-increment. In the Register
File, registers R26 to R31 feature the indirect addressing pointer registers.
The direct addressing reaches the entire data space.
The Indirect with Displacement mode reaches 63 address locations from the base address given
by the Y- or Z-register.
When using register indirect addressing modes with automatic pre-decrement and post-incre-
ment, the address registers X, Y, and Z are decremented or incremented.
The 32 general purpose working registers, 64 (+160) I/O Registers, and the 1024 bytes of inter-
nal data SRAM in the ATmega162 are all accessible through all these addressing modes. The
Register File is described in “General Purpose Register File” on page 12.
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Figure 9. Data Memory Map
Data Memory Access
Times
This section describes the general access timing concepts for internal memory access. The
internal data SRAM access is performed in two clkCPU cycles as described in Figure 10.
Figure 10. On-chip Data SRAM Access Cycles
EEPROM Data
Memory
The ATmega162 contains 512 bytes of data EEPROM memory. It is organized as a separate
data space, in which single bytes can be read and written. The EEPROM has an endurance of at
least 100,000 write/erase cycles. The access between the EEPROM and the CPU is described
in the following, specifying the EEPROM Address Registers, the EEPROM Data Register, and
the EEPROM Control Register.
clk
WR
RD
Data
Data
Address Address valid
T1 T2 T3
Compute Address
Read Write
CPU
Memory Access Instruction Next Instruction
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“Memory Programming” on page 231 contains a detailed description on EEPROM Programming
in SPI, JTAG, or Parallel Programming mode.
EEPROM Read/Write
Access
The EEPROM Access Registers are accessible in the I/O space.
The write access time for the EEPROM is given in Table 1. A selftiming function, however, lets
the user software detect when the next byte can be written. If the user code contains instructions
that write the EEPROM, some precautions must be taken. In heavily filtered power supplies, VCC
is likely to rise or fall slowly on Power-up/down. This causes the device for some period of time
to run at a voltage lower than specified as minimum for the clock frequency used. See “Prevent-
ing EEPROM Corruption” on page 24 for details on how to avoid problems in these situations.
In order to prevent unintentional EEPROM writes, a specific write procedure must be followed.
Refer to the description of the EEPROM Control Register for details on this.
When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction is
executed. When the EEPROM is written, the CPU is halted for two clock cycles before the next
instruction is executed.
The EEPROM Address
Register – EEARH and
EEARL
• Bits 15..9 – Res: Reserved Bits
These bits are reserved bits in the ATmega162 and will always read as zero.
• Bits 8..0 – EEAR8..0: EEPROM Address
The EEPROM Address Registers – EEARH and EEARL specify the EEPROM address in the
512 bytes EEPROM space. The EEPROM data bytes are addressed linearly between 0 and
511. The initial value of EEAR is undefined. A proper value must be written before the EEPROM
may be accessed.
Bit 151413121110 9 8
–––––––EEAR8EEARH
EEAR7 EEAR6 EEAR5 EEAR4 EEAR3 EEAR2 EEAR1 EEAR0 EEARL
76543210
Read/WriteRRRRRRRR/W
R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value0000000X
XXXXXXXX
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The EEPROM Data
Register – EEDR
• Bits 7..0 – EEDR7.0: EEPROM Data
For the EEPROM write operation, the EEDR Register contains the data to be written to the
EEPROM in the address given by the EEAR Register. For the EEPROM read operation, the
EEDR contains the data read out from the EEPROM at the address given by EEAR.
The EEPROM Control
Register – EECR
• Bits 7..4 – Res: Reserved Bits
These bits are reserved bits in the ATmega162 and will always read as zero.
• Bit 3 – EERIE: EEPROM Ready Interrupt Enable
Writing EERIE to one enables the EEPROM Ready Interrupt if the I bit in SREG is set. Writing
EERIE to zero disables the interrupt. The EEPROM Ready interrupt generates a constant inter-
rupt when EEWE is cleared.
• Bit 2 – EEMWE: EEPROM Master Write Enable
The EEMWE bit determines whether setting EEWE to one causes the EEPROM to be written.
When EEMWE is set, setting EEWE within four clock cycles will write data to the EEPROM at
the selected address. If EEMWE is zero, setting EEWE will have no effect. When EEMWE has
been written to one by software, hardware clears the bit to zero after four clock cycles. See the
description of the EEWE bit for an EEPROM write procedure.
• Bit 1 – EEWE: EEPROM Write Enable
The EEPROM Write Enable signal EEWE is the write strobe to the EEPROM. When address
and data are correctly set up, the EEWE bit must be written to one to write the value into the
EEPROM. The EEMWE bit must be written to one before a logical one is written to EEWE, oth-
erwise no EEPROM write takes place. The following procedure should be followed when writing
the EEPROM (the order of steps 3 and 4 is not essential):
1. Wait until EEWE becomes zero.
2. Wait until SPMEN in SPMCR becomes zero.
3. Write new EEPROM address to EEAR (optional).
4. Write new EEPROM data to EEDR (optional).
5. Write a logical one to the EEMWE bit while writing a zero to EEWE in EECR.
6. Within four clock cycles after setting EEMWE, write a logical one to EEWE.
The EEPROM can not be programmed during a CPU write to the Flash memory. The software
must check that the Flash programming is completed before initiating a new EEPROM write.
Step 2 is only relevant if the software contains a Boot Loader allowing the CPU to program the
Flash. If the Flash is never being updated by the CPU, step 2 can be omitted. See “Boot Loader
Support – Read-While-Write Self-programming” on page 217 for details about boot
programming.
Bit 76543210
MSB LSB EEDR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
– – – – EERIE EEMWE EEWE EERE EECR
Read/Write R R R R R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 X 0
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Caution: An interrupt between step 5 and step 6 will make the write cycle fail, since the
EEPROM Master Write Enable will time-out. If an interrupt routine accessing the EEPROM is
interrupting another EEPROM access, the EEAR or EEDR Register will be modified, causing the
interrupted EEPROM access to fail. It is recommended to have the Global Interrupt Flag cleared
during all the steps to avoid these problems.
When the write access time has elapsed, the EEWE bit is cleared by hardware. The user soft-
ware can poll this bit and wait for a zero before writing the next byte. When EEWE has been set,
the CPU is halted for two cycles before the next instruction is executed.
• Bit 0 – EERE: EEPROM Read Enable
The EEPROM Read Enable Signal EERE is the read strobe to the EEPROM. When the correct
address is set up in the EEAR Register, the EERE bit must be written to a logic one to trigger the
EEPROM read. The EEPROM read access takes one instruction, and the requested data is
available immediately. When the EEPROM is read, the CPU is halted for four cycles before the
next instruction is executed.
The user should poll the EEWE bit before starting the read operation. If a write operation is in
progress, it is neither possible to read the EEPROM, nor to change the EEAR Register.
The calibrated Oscillator is used to time the EEPROM accesses. Table 1 lists the typical pro-
gramming time for EEPROM access from the CPU.
Note: 1. Uses 1 MHz clock, independent of CKSEL Fuse settings
Table 1. EEPROM Programming Time
Symbol
Number of Calibrated RC
Oscillator Cycles(1) Typ Programming Time
EEPROM write (from CPU) 8448 8.5 ms
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The following code examples show one assembly and one C function for writing to the
EEPROM. The examples assume that interrupts are controlled (e.g., by disabling interrupts
globally) so that no interrupts will occur during execution of these functions. The examples also
assume that no Flash Boot Loader is present in the software. If such code is present, the
EEPROM write function must also wait for any ongoing SPM command to finish.
Assembly Code Example
EEPROM_write:
; Wait for completion of?previous write
sbic EECR,EEWE
rjmp EEPROM_write
; Set up address (r18:r1?) in address register
out EEARH, r18
out EEARL, r17
; Write data (r16) to da?a register
out EEDR,r16
; Write logical one to E?MWE
sbi EECR,EEMWE
; Start eeprom write by ?etting EEWE
sbi EECR,EEWE
ret
C Code Example
void EEPROM_write(unsigned int uiAddress, unsigned char ucData)
{
/* Wait for complet?on of previous write */
while(EECR & (1<<EEWE))
;
/* Set up address and da?a registers */
EEAR = uiAddress;
EEDR = ucData;
/* Write logical on? to EEMWE */
EECR |= (1<<EEMWE);
/* Start eeprom write by?setting EEWE */
EECR |= (1<<EEWE);
}
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The next code examples show assembly and C functions for reading the EEPROM. The exam-
ples assume that interrupts are controlled so that no interrupts will occur during execution of
these functions.
EEPROM Write During
Power-down Sleep
Mode
When entering Power-down sleep mode while an EEPROM write operation is active, the
EEPROM write operation will continue, and will complete before the write access time has
passed. However, when the write operation is complete, the Oscillator continues running, and as
a consequence, the device does not enter Power-down entirely. It is therefore recommended to
verify that the EEPROM write operation is completed before entering Power-down.
Preventing EEPROM
Corruption
During periods of low VCC, the EEPROM data can be corrupted because the supply voltage is
too low for the CPU and the EEPROM to operate properly. These issues are the same as for
board level systems using EEPROM, and the same design solutions should be applied.
An EEPROM data corruption can be caused by two situations when the voltage is too low. First,
a regular write sequence to the EEPROM requires a minimum voltage to operate correctly. Sec-
ondly, the CPU itself can execute instructions incorrectly, if the supply voltage is too low.
EEPROM data corruption can easily be avoided by following this design recommendation:
Keep the AVR RESET active (low) during periods of insufficient power supply voltage. This can
be done by enabling the internal Brown-out Detector (BOD). If the detection level of the internal
BOD does not match the needed detection level, an external low VCC Reset Protection circuit
can be used. If a Reset occurs while a write operation is in progress, the write operation will be
completed provided that the power supply voltage is sufficient.
Assembly Code Example
EEPROM_read:
; Wait for completion of?previous write
sbic EECR,EEWE
rjmp EEPROM_read
; Set up address (r18:r1?) in address register
out EEARH, r18
out EEARL, r17
; Start eeprom read by w?iting EERE
sbi EECR,EERE
; Read data from data re?ister
in r16,EEDR
ret
C Code Example
unsigned char EEPROM_read(unsigned int uiAddress)
{
/* Wait for completion o? previous write */
while(EECR & (1<<EEWE))
;
/* Set up address regist?r */
EEAR = uiAddress;
/* Start eeprom rea? by writing EERE */
EECR |= (1<<EERE);
/* Return data from data?register */
return EEDR;
}
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I/O Memory The I/O space definition of the ATmega162 is shown in “Register Summary” on page 304.
All ATmega162 I/Os and peripherals are placed in the I/O space. All I/O locations may be
accessed by the LD/LDS/LDD and ST/STS/STD instructions, transferring data between the 32
general purpose working registers and the I/O space. I/O Registers within the address range
0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these registers, the
value of single bits can be checked by using the SBIS and SBIC instructions. Refer to the
instruction set section for more details. When using the I/O specific commands IN and OUT, the
I/O addresses 0x00 - 0x3F must be used. When addressing I/O Registers as data space using
LD and ST instructions, 0x20 must be added to these addresses. The ATmega162 is a complex
microcontroller with more peripheral units than can be supported within the 64 location reserved
in Opcode for the IN and OUT instructions. For the Extended I/O space from 0x60 - 0xFF in
SRAM, only the ST/STS/STD and LD/LDS/LDD instructions can be used. The Extended I/O
space is replaced with SRAM locations when the ATmega162 is in the ATmega161 compatibility
mode.
For compatibility with future devices, reserved bits should be written to zero if accessed.
Reserved I/O memory addresses should never be written.
Some of the Status Flags are cleared by writing a logical one to them. Note that the CBI and SBI
instructions will operate on all bits in the I/O Register, writing a one back into any flag read as
set, thus clearing the flag. The CBI and SBI instructions work with registers 0x00 to 0x1F only.
The I/O and peripherals control registers are explained in later sections.
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External Memory
Interface
With all the features the External Memory Interface provides, it is well suited to operate as an
interface to memory devices such as external SRAM and FLASH, and peripherals such as LCD-
display, A/D, and D/A. The main features are:
•Four Different Wait-state Settings (Including No Wait-state)
•Independent Wait-state Setting for Different External Memory Sectors (Configurable Sector Size)
•The Number of Bits Dedicated to Address High Byte is Selectable
•Bus Keepers on Data Lines to Minimize Current Consumption (Optional)
Overview When the eXternal MEMory (XMEM) is enabled, address space outside the internal SRAM
becomes available using the dedicated external memory pins (see Figure 1 on page 2, Table 29
on page 70, Table 35 on page 75, and Table 41 on page 81). The memory configuration is
shown in Figure 11.
Figure 11. External Memory with Sector Select
Note: 1. Address depends on the ATmega161 compatibility Fuse. See “SRAM Data Memory” on page
18 and Figure 9 on page 19 for details.
Using the External
Memory Interface
The interface consists of:
• AD7:0: Multiplexed low-order address bus and data bus
• A15:8: High-order address bus (configurable number of bits)
• ALE: Address latch enable
•RD
: Read strobe.
•WR
: Write strobe.
0x0000
0x04FF/0x045F
(1)
External Memory
(0-64K x 8)
0xFFFF
Internal Memory
SRL[2..0]
SRW11
SRW10
SRW01
SRW00
Lower Sector
Upper Sector
0x0500/0x0460
(1)
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The control bits for the External Memory Interface are located in three registers, the MCU Con-
trol Register – MCUCR, the Extended MCU Control Register – EMCUCR, and the Special
Function IO Register – SFIOR.
When the XMEM interface is enabled, it will override the settings in the Data Direction registers
corresponding to the ports dedicated to the interface. For details about this port override, see the
alternate functions in section “I/O-Ports” on page 63. The XMEM interface will autodetect
whether an access is internal or external. If the access is external, the XMEM interface will out-
put address, data, and the control signals on the ports according to Figure 13 (this figure shows
the wave forms without wait-states). When ALE goes from high to low, there is a valid address
on AD7:0. ALE is low during a data transfer. When the XMEM interface is enabled, also an inter-
nal access will cause activity on address-, data- and ALE ports, but the RD and WR strobes will
not toggle during internal access. When the External Memory Interface is disabled, the normal
pin and data direction settings are used. Note that when the XMEM interface is disabled, the
address space above the internal SRAM boundary is not mapped into the internal SRAM. Figure
12 illustrates how to connect an external SRAM to the AVR using an octal latch (typically
“74x573” or equivalent) which is transparent when G is high.
Address Latch
Requirements
Due to the high-speed operation of the XRAM interface, the address latch must be selected with
care for system frequencies above 8 MHz @ 4V and 4 MHz @ 2.7V. When operating at condi-
tions above these frequencies, the typical old style 74HC series latch becomes inadequate. The
external memory interface is designed in compliance to the 74AHC series latch. However, most
latches can be used as long they comply with the main timing parameters. The main parameters
for the address latch are:
• D to Q propagation delay (tpd).
• Data setup time before G low (tsu).
• Data (address) hold time after G low (th).
The external memory interface is designed to guaranty minimum address hold time after G is
asserted low of th = 5 ns (refer to tLAXX_LD/tLLAXX_ST in Table 114 to Table 121 on page 272). The
D to Q propagation delay (tpd) must be taken into consideration when calculating the access time
requirement of the external component. The data setup time before G low (tsu) must not exceed
address valid to ALE low (tAVLLC) minus PCB wiring delay (dependent on the capacitive load).
Figure 12. External SRAM Connected to the AVR
D[7:0]
A[7:0]
A[15:8]
RD
WR
SRAM
DQ
G
AD7:0
ALE
A15:8
RD
WR
AVR
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Pull-up and Bus
Keeper
The pull-up resistors on the AD7:0 ports may be activated if the corresponding Port register is
written to one. To reduce power consumption in sleep mode, it is recommended to disable the
pull-ups by writing the Port register to zero before entering sleep.
The XMEM interface also provides a bus keeper on the AD7:0 lines. The Bus Keeper can be dis-
abled and enabled in software as described in “Special Function IO Register – SFIOR” on page
32. When enabled, the Bus Keeper will keep the previous value on the AD7:0 bus while these
lines are tri-stated by the XMEM interface.
Timing External memory devices have various timing requirements. To meet these requirements, the
ATmega162 XMEM interface provides four different wait-states as shown in Table 3. It is impor-
tant to consider the timing specification of the external memory device before selecting the wait-
state. The most important parameters are the access time for the external memory in conjunc-
tion with the set-up requirement of the ATmega162. The access time for the external memory is
defined to be the time from receiving the chip select/address until the data of this address actu-
ally is driven on the bus. The access time cannot exceed the time from the ALE pulse is asserted
low until data must be stable during a read sequence (tLLRL+ tRLRH - tDVRH in Table 114 to Table
121 on page 272). The different wait-states are set up in software. As an additional feature, it is
possible to divide the external memory space in two sectors with individual wait-state settings.
This makes it possible to connect two different memory devices with different timing require-
ments to the same XMEM interface. For XMEM interface timing details, please refer to Figure
118 to Figure 121, and Table 114 to Table 121.
Note that the XMEM interface is asynchronous and that the waveforms in the figures below are
related to the internal system clock. The skew between the internal and external clock (XTAL1)
is not guaranteed (it varies between devices, temperature, and supply voltage). Consequently,
the XMEM interface is not suited for synchronous operation.
Figure 13. External Data Memory Cycles without Wait-state
(SRWn1 = 0 and SRWn0 =0)(1)
Note: 1. SRWn1 = SRW11 (upper sector) or SRW01 (lower sector), SRWn0 = SRW10 (upper sector) or
SRW00 (lower sector).
The ALE pulse in period T4 is only present if the next instruction accesses the RAM (internal
or external).
ALE
T1 T2 T3
Write
Read
WR
T4
A15:8
AddressPrev. addr.
DA7:0
Address DataPrev. data XX
RD
DA7:0 (XMBK = 0)
DataAddress
DataPrev. data Address
DA7:0 (XMBK = 1)
System Clock (CLKCPU)
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Figure 14. External Data Memory Cycles with SRWn1 = 0 and SRWn0 = 1(1)
Note: 1. SRWn1 = SRW11 (upper sector) or SRW01 (lower sector), SRWn0 = SRW10 (upper sector) or
SRW00 (lower sector)
The ALE pulse in period T5 is only present if the next instruction accesses the RAM (internal
or external).
Figure 15. External Data Memory Cycles with SRWn1 = 1 and SRWn0 = 0(1)
Note: 1. SRWn1 = SRW11 (upper sector) or SRW01 (lower sector), SRWn0 = SRW10 (upper sector) or
SRW00 (lower sector).
The ALE pulse in period T6 is only present if the next instruction accesses the RAM (internal
or external).
ALE
T1 T2 T3
Write
Read
WR
T5
A15:8 AddressPrev. addr.
DA7:0 Address DataPrev. data XX
RD
DA7:0 (XMBK = 0) DataAddress
DataPrev. data Address
DA7:0 (XMBK = 1)
System Clock (CLK
CPU
)
T4
ALE
T1 T2 T3
Write
Read
WR
T6
A15:8 AddressPrev. addr.
DA7:0 Address DataPrev. data XX
RD
DA7:0 (XMBK = 0) DataAddress
DataPrev. data Address
DA7:0 (XMBK = 1)
System Clock (CLK
CPU
)
T4 T5
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Figure 16. External Data Memory Cycles with SRWn1 = 1 and SRWn0 = 1(1)
Note: 1. SRWn1 = SRW11 (upper sector) or SRW01 (lower sector), SRWn0 = SRW10 (upper sector) or
SRW00 (lower sector).
The ALE pulse in period T7 is only present if the next instruction accesses the RAM (internal
or external).
XMEM Register
Description
MCU Control Register
– MCUCR
• Bit 7 – SRE: External SRAM/XMEM Enable
Writing SRE to one enables the External Memory Interface.The pin functions AD7:0, A15:8,
ALE, WR, and RD are activated as the alternate pin functions. The SRE bit overrides any pin
direction settings in the respective Data Direction Registers. Writing SRE to zero, disables the
External Memory Interface and the normal pin and data direction settings are used.
• Bit 6 – SRW10: Wait State Select Bit
For a detailed description, see common description for the SRWn bits below (EMCUCR
description).
Extended MCU
Control Register –
EMCUCR
• Bit 6..4 – SRL2, SRL1, SRL0: Wait State Sector Limit
It is possible to configure different wait-states for different external memory addresses. The
external memory address space can be divided in two sectors that have separate wait-state bits.
The SRL2, SRL1, and SRL0 bits select the splitting of these sectors, see Table 2 and Figure 11.
By default, the SRL2, SRL1, and SRL0 bits are set to zero and the entire external memory
address space is treated as one sector. When the entire SRAM address space is configured as
one sector, the wait-states are configured by the SRW11 and SRW10 bits.
ALE
T1 T2 T3
Write
Read
WR
T7
A15:8 AddressPrev. addr.
DA7:0 Address DataPrev. data XX
RD
DA7:0 (XMBK = 0) DataAddress
DataPrev. data Address
DA7:0 (XMBK = 1)
System Clock (CLK
CPU
)
T4 T5 T6
Bit 76543210
SRE SRW10 SE SM1 ISC11 ISC10 ISC01 ISC00 MCUCR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
SM0 SRL2 SRL1 SRL0 SRW01 SRW00 SRW11 ISC2 EMCUCR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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• Bit 1 and Bit 6 MCUCR – SRW11, SRW10: Wait-state Select Bits for Upper Sector
The SRW11 and SRW10 bits control the number of wait-states for the upper sector of the exter-
nal memory address space, see Table 3.
• Bit 3..2 – SRW01, SRW00: Wait-state Select Bits for Lower Sector
The SRW01 and SRW00 bits control the number of wait-states for the lower sector of the exter-
nal memory address space, see Table 3.
Note: 1. n = 0 or 1 (lower/upper sector).
For further details of the timing and wait-states of the External Memory Interface, see Figure
13 to Figure 16 how the setting of the SRW bits affects the timing.
Table 2. Sector Limits with Different Settings of SRL2..0
SRL2 SRL1 SRL0 Sector Limits
000Lower sector = N/A
Upper sector = 0x1100 - 0xFFFF
001Lower sector = 0x1100 - 0x1FFF
Upper sector = 0x2000 - 0xFFFF
010Lower sector = 0x1100 - 0x3FFF
Upper sector = 0x4000 - 0xFFFF
011Lower sector = 0x1100 - 0x5FFF
Upper sector = 0x6000 - 0xFFFF
100Lower sector = 0x1100 - 0x7FFF
Upper sector = 0x8000 - 0xFFFF
101Lower sector = 0x1100 - 0x9FFF
Upper sector = 0xA000 - 0xFFFF
110Lower sector = 0x1100 - 0xBFFF
Upper sector = 0xC000 - 0xFFFF
111Lower sector = 0x1100 - 0xDFFF
Upper sector = 0xE000 - 0xFFFF
Table 3. Wait-states(1)
SRWn1 SRWn0 Wait-states
0 0 No wait-states
0 1 Wait one cycle during read/write strobe
1 0 Wait two cycles during read/write strobe
11Wait two cycles during read/write and wait one cycle before driving out
new address
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Special Function IO
Register – SFIOR
• Bit 6 – XMBK: External Memory Bus Keeper Enable
Writing XMBK to one enables the Bus Keeper on the AD7:0 lines. When the Bus Keeper is
enabled, AD7:0 will keep the last driven value on the lines even if the XMEM interface has tri-
stated the lines. Writing XMBK to zero disables the Bus Keeper. XMBK is not qualified with SRE,
so even if the XMEM interface is disabled, the bus keepers are still activated as long as XMBK is
one.
• Bit 6..3 – XMM2, XMM1, XMM0: External Memory High Mask
When the External Memory is enabled, all Port C pins are used for the high address byte by
default. If the full 60KB address space is not required to access the external memory, some, or
all, Port C pins can be released for normal Port Pin function as described in Table 4. As
described in “Using all 64KB Locations of External Memory” on page 34, it is possible to use the
XMMn bits to access all 64KB locations of the external memory.
Using all Locations of
External Memory
Smaller than 64 KB
Since the external memory is mapped after the internal memory as shown in Figure 11, the
external memory is not addressed when addressing the first 1,280 bytes of data space. It may
appear that the first 1,280 bytes of the external memory are inaccessible (external memory
addresses 0x0000 to 0x04FF). However, when connecting an external memory smaller than 64
KB, for example 32 KB, these locations are easily accessed simply by addressing from address
0x8000 to 0x84FF. Since the External Memory Address bit A15 is not connected to the external
memory, addresses 0x8000 to 0x84FF will appear as addresses 0x0000 to 0x04FF for the exter-
nal memory. Addressing above address 0x84FF is not recommended, since this will address an
external memory location that is already accessed by another (lower) address. To the Applica-
tion software, the external 32 KB memory will appear as one linear 32 KB address space from
0x0500 to 0x84FF. This is illustrated in Figure 17. Memory configuration B refers to the
ATmega161 compatibility mode, configuration A to the non-compatible mode.
Bit 7654321 0
TSM XMBK XMM2 XMM1 XMM0 PUD PSR2 PSR310 SFIOR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Table 4. Port C Pins Released as Normal Port Pins when the External Memory is Enabled
XMM2 XMM1 XMM0 # Bits for External Memory Address Released Port Pins
0008 (Full 60 KB space) None
0017 PC7
0106 PC7 - PC6
0115 PC7 - PC5
1004 PC7 - PC4
1013 PC7 - PC3
1102 PC7 - PC2
111No Address high bits Full Port C
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When the device is set in ATmega161 compatibility mode, the internal address space is 1,120
bytes. This implies that the first 1,120 bytes of the external memory can be accessed at
addresses 0x8000 to 0x845F. To the Application software, the external 32 KB memory will
appear as one linear 32 KB address space from 0x0460 to 0x845F.
Figure 17. Address Map with 32 KB External Memory
0x0000
0x04FF
0xFFFF
0x0500
0x7FFF
0x8000
0x84FF
0x8500
0x0000
0x04FF
0x0500
0x7FFF
Memory Configuration A Memory Configuration B
Internal Memory
(Unused)
AVR Memory Map External 32K SRAM
External
Memory
0x0000
0x045F
0xFFFF
0x0460
0x7FFF
0x8000
0x845F
0x8460
0x0000
0x045F
0x0460
0x7FFF
Internal Memory
(Unused)
AVR Memory Map External 32K SRAM
External
Memory
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ATmega162/V
Using all 64KB
Locations of External
Memory
Since the external memory is mapped after the internal memory as shown in Figure 11, only
64,256 Bytes of external memory are available by default (address space 0x0000 to 0x04FF is
reserved for internal memory). However, it is possible to take advantage of the entire external
memory by masking the higher address bits to zero. This can be done by using the XMMn bits
and control by software the most significant bits of the address. By setting Port C to output 0x00,
and releasing the most significant bits for normal Port Pin operation, the Memory Interface will
address 0x0000 - 0x1FFF. See code example below.
Note: 1. The example code assumes that the part specific header file is included.
Care must be exercised using this option as most of the memory is masked away.
Assembly Code Example(1)
; OFFSET is defined to 0?2000 to ensure
; external memory access
; Configure Port C (addr?ss high byte) to
; output 0x00 when the p?ns are released
; for normal Port Pin op?ration
ldi r16, 0xFF
out DDRC, r16
ldi r16, 0x00
out PORTC, r16
; release PC7:5
ldi r16, (1<<XMM1)|(1<<XMM0)
out SFIOR, r16
; write 0xAA to address ?x0001 of external
; memory
ldi r16, 0xaa
sts 0x0001+OFFSET, r16
; re-enable PC7:5 for ex?ernal memory
ldi r16, (0<<XMM1)|(0<<XMM0)
out SFIOR, r16
; store 0x55 to address ?OFFSET + 1) of
; external memory
ldi r16, 0x55
sts 0x0001+OFFSET, r16
C Code Example(1)
#define OFFSET 0x2000
void XRAM_example(void)
{
unsigned char *p = (unsigned char *) (OFFSET + 1);
DDRC = 0xFF;
PORTC = 0x00;
SFIOR = (1<<XMM1) | (1<<XMM0);
*p = 0xaa;
SFIOR = 0x00;
*p = 0x55;
}
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System Clock
and Clock
Options
Clock Systems
and their
Distribution
Figure 18 presents the principal clock systems in the AVR and their distribution. All of the clocks
need not be active at a given time. In order to reduce power consumption, the clocks to modules
not being used can be halted by using different sleep modes, as described in “Power Manage-
ment and Sleep Modes” on page 43. The clock systems are detailed below.
Figure 18. Clock Distribution
CPU clock – clkCPU The CPU clock is routed to parts of the system concerned with operation of the AVR core.
Examples of such modules are the General Purpose Register File, the Status Register and the
data memory holding the Stack Pointer. Halting the CPU clock inhibits the core from performing
general operations and calculations.
I/O clock – clkI/O The I/O clock is used by the majority of the I/O modules, like Timer/Counters, SPI, and USART.
The I/O clock is also used by the External Interrupt module, but note that some external inter-
rupts are detected by asynchronous logic, allowing such interrupts to be detected even if the I/O
clock is halted.
Flash clock – clkFLASH The Flash clock controls operation of the Flash interface. The Flash clock is usually active simul-
taneously with the CPU clock.
Asynchronous Timer
clock – clkASY
The Asynchronous Timer clock allows the Asynchronous Timer/Counter to be clocked directly
from an external 32 kHz clock crystal. The dedicated clock domain allows using this
Timer/Counter as a realtime counter even when the device is in sleep mode.
General I/O
Modules
Asynchronous
Timer/Counter CPU Core RAM
clk
I/O
clk
ASY
AVR Clock
Control Unit
clk
CPU
Flash and
EEPROM
clk
FLASH
Source clock
Watchdog Timer
Watchdog
Oscillator
Reset Logic
Clock
Multiplexer
Watchdog clock
Calibrated RC
Oscillator
Timer/Counter
Oscillator
Crystal
Oscillator
Low-frequency
Crystal Oscillator
External Clock
System Clock
Prescaler
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Clock Sources The device has the following clock source options, selectable by Flash Fuse bits as shown
below. The clock from the selected source is input to the AVR clock generator, and routed to the
appropriate modules.
Note: For all fuses “1” means unprogrammed while “0” means programmed.
The various choices for each clocking option is given in the following sections. When the CPU
wakes up from Power-down or Power-save, the selected clock source is used to time the start-
up, ensuring stable Oscillator operation before instruction execution starts. When the CPU starts
from Reset, there is an additional delay allowing the power to reach a stable level before com-
mencing normal operation. The Watchdog Oscillator is used for timing this realtime part of the
start-up time. The number of WDT Oscillator cycles used for each Time-out is shown in Table 6.
The frequency of the Watchdog Oscillator is voltage dependent as shown in “ATmega162 Typi-
cal Characteristics” on page 275.
Default Clock
Source
The device is shipped with CKSEL = “0010”, SUT = “10” and CKDIV8 programmed. The default
clock source setting is therefore the Internal RC Oscillator with longest startup time and an initial
system clock prescaling of 8. This default setting ensures that all users can make their desired
clock source setting using an In-System or Parallel programmer.
Crystal Oscillator XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be con-
figured for use as an On-chip Oscillator, as shown in Figure 19. Either a quartz crystal or a
ceramic resonator may be used.
C1 and C2 should always be equal for both crystals and resonators. The optimal value of the
capacitors depends on the crystal or resonator in use, the amount of stray capacitance, and the
electromagnetic noise of the environment. Some initial guidelines for choosing capacitors for
use with crystals are given in Table 7. For ceramic resonators, the capacitor values given by the
manufacturer should be used.
Table 5. Device Clocking Options Select
Device Clocking Option CKSEL3..0
External Crystal/Ceramic Resonator 1111 - 1000
External Low-frequency Crystal 0111 - 0100
Calibrated Internal RC Oscillator 0010
External Clock 0000
Reserved 0011, 0001
Table 6. Number of Watchdog Oscillator Cycles
Typ Time-out (VCC = 5.0V) Typ Time-out (VCC = 3.0V) Number of Cycles
4.1 ms 4.3 ms 4K (4,096)
65 ms 69 ms 64K (65,536)
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Figure 19. Crystal Oscillator Connections
The Oscillator can operate in four different modes, each optimized for a specific frequency
range. The operating mode is selected by the fuses CKSEL3:1 as shown in Table 7.
Note: 1. This option should not be used with crystals, only with ceramic resonators.
The CKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown in Table
8.
Table 7. Crystal Oscillator Operating Modes
CKSEL3:1
Frequency Range
(MHz)
Recommended Range for Capacitors C1 and
C2 for Use with Crystals (pF)
100(1) 0.4 - 0.9 –
101 0.9 - 3.0 12 - 22
110 3.0 - 8.0 12 - 22
111 8.0 - 12 - 22
Table 8. Start-up Times for the Crystal Oscillator Clock Selection
CKSEL0 SUT1:0
Start-up Time from
Power-down and
Power-save
Additional Delay from
Reset (VCC = 5.0V)
Recommended
Usage
0 00 258 CK(1) 4.1 ms Ceramic resonator,
fast rising power
0 01 258 CK(1) 65 ms Ceramic resonator,
slowly rising power
010 1K CK
(2) – Ceramic resonator,
BOD enabled
011 1K CK
(2) 4.1 ms Ceramic resonator,
fast rising power
100 1K CK
(2) 65 ms Ceramic resonator,
slowly rising power
1 01 16K CK – Crystal Oscillator,
BOD enabled
1 10 16K CK 4.1 ms Crystal Oscillator,
fast rising power
1 11 16K CK 65 ms Crystal Oscillator,
slowly rising power
XTAL2
XTAL1
GND
C2
C1
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Notes: 1. These options should only be used when not operating close to the maximum frequency of the
device, and only if frequency stability at start-up is not important for the application. These
options are not suitable for crystals.
2. These options are intended for use with ceramic resonators and will ensure frequency stability
at start-up. They can also be used with crystals when not operating close to the maximum fre-
quency of the device, and if frequency stability at start-up is not important for the application.
Low-frequency
Crystal Oscillator
To use a 32.768 kHz watch crystal as the clock source for the device, the Low-frequency Crystal
Oscillator must be selected by setting the CKSEL Fuses to “0100”, “0101”, “0110” or “0111”. The
crystal should be connected as shown in Figure 19. If CKSEL equals “0110” or “0111”, the inter-
nal capacitors on XTAL1 and XTAL2 are enabled, thereby removing the need for external
capacitors. The internal capacitors have a nominal value of 10 pF.
When this Oscillator is selected, start-up times are determined by the SUT Fuses (real time-out
from Reset) and CKSEL0 (number of clock cycles) as shown in Table 9 and Table 10.
Note: 1. These options should only be used if frequency stability at start-up is not important for the
application.
Calibrated Internal
RC Oscillator
The calibrated internal RC Oscillator provides a fixed 8.0 MHz clock. The frequency is nominal
value at 3V and 25°C. If 8.0 MHz frequency exceed the specification of the device (depends on
VCC), the CKDIV8 Fuse must be programmed in order to divide the internal frequency by 8 dur-
ing start-up. See “System Clock Prescaler” on page 41 for more details. This clock may be
selected as the system clock by programming the CKSEL Fuses as shown in Table 11. If
selected, it will operate with no external components. During Reset, hardware loads the calibra-
tion byte into the OSCCAL Register and thereby automatically calibrates the RC Oscillator. At
3V and 25°C, this calibration gives a frequency within ±10% of the nominal frequency. Using cal-
ibration methods as described in application notes available at www.atmel.com/avr it is possible
to achieve ±2% accuracy at any given VCC and Temperature. When this Oscillator is used as the
chip clock, the Watchdog Oscillator will still be used for the Watchdog Timer and for the Reset
Table 9. Start-up Delay from Reset when Low-frequency Crystal Oscillator is Selected
SUT1:0 Additional Delay from Reset (VCC = 5.0V) Recommended Usage
00 0 ms Fast rising power or BOD enabled
01 4.1 ms Fast rising power or BOD enabled
10 65 ms Slowly rising power
11 Reserved
Table 10. Start-up Times for the Low-frequency Crystal Oscillator Clock Selection
CKSEL1:0
Internal Capacitors
Enabled?
Start-up Time from
Power-down and
Power-save Recommended Usage
00(1) No 1K CK
01 No 32K CK Stable Frequency at start-up
10(1) Ye s 1 K C K
11 Yes 32K CK Stable Frequency at start-up
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Time-out. For more information on the pre-programmed calibration value, see the section “Cali-
bration Byte” on page 234.
Note: 1. The device is shipped with this option selected.
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 12. XTAL1 and XTAL2 should be left unconnected (NC).
Note: 1. The device is shipped with this option selected.
Oscillator Calibration
Register – OSCCAL
• Bit 7 – Res: Reserved Bit
This bit is reserved bit in the ATmega162, and will always read as zero.
• Bits 6..0 – CAL6..0: Oscillator Calibration Value
Writing the calibration byte to this address will trim the Internal Oscillator to remove process vari-
ations from the Oscillator frequency. This is done automatically during Chip Reset. When
OSCCAL is zero, the lowest available frequency is chosen. Writing non-zero values to this regis-
ter will increase the frequency of the Internal Oscillator. Writing 0x7F to the register gives the
highest available frequency. The calibrated Oscillator is used to time EEPROM and Flash
access. If EEPROM or Flash is written, do not calibrate to more than 10% above the nominal fre-
quency. Otherwise, the EEPROM or Flash write may fail.
Table 11. Internal Calibrated RC Oscillator Operating Modes
CKSEL3:0 Nominal Frequency
0010(1) 8.0 MHz
Table 12. Start-up Times for the Internal Calibrated RC Oscillator Clock Selection
SUT1:0
Start-up Time from Power-
down and Power-save
Additional Delay from
Reset (VCC = 5.0V) Recommended Usage
00 6 CK – BOD enabled
01 6 CK 4.1 ms Fast rising power
10(1) 6 CK 65 ms Slowly rising power
11 Reserved
Bit 76543210
– CAL6 CAL5 CAL4 CAL3 CAL2 CAL1 CAL0 OSCCAL
Read/Write R R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 Device Specific Calibration Value
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External Clock To drive the device from an external clock source, XTAL1 should be driven as shown in Figure
20. To run the device on an external clock, the CKSEL Fuses must be programmed to “0000”.
Figure 20. External Clock Drive Configuration
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table 14.
When applying an external clock, it is required to avoid sudden changes in the applied clock fre-
quency to ensure stable operation of the MCU. A variation in frequency of more than 2% from
one clock cycle to the next can lead to unpredictable behavior. It is required to ensure that the
MCU is kept in reset during such changes in the clock frequency.
Note that the System Clock Prescaler can be used to implement run-time changes of the internal
clock frequency while still ensuring stable operation. Refer to “System Clock Prescaler” on page
41 for details.
Clock output
buffer
When the CKOUT Fuse is programmed, the system clock will be output on PortB 0. This mode is
suitable when chip clock is used to drive other circuits on the system. The clock will be output
also during Reset and the normal operation of PortB will be overridden when the fuse is pro-
Table 13. Internal RC Oscillator Frequency Range.
OSCCAL Value
Min Frequency in Percentage of
Nominal Frequency
Max Frequency in Percentage of
Nominal Frequency
0x00 50% 100%
0x3F 75% 150%
0x7F 100% 200%
Table 14. Start-up Times for the External Clock Selection
SUT1..0
Start-up Time from
Power-down and
Power-save
Additional Delay from
Reset (VCC = 5.0V) Recommended Usage
00 6 CK – BOD enabled
01 6 CK 4.1 ms Fast rising power
10 6 CK 65 ms Slowly rising power
11 Reserved
EXTERNAL
CLOCK
SIGNAL
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grammed. Any clock sources, including Internal RC Oscillator, can be selected when PortB 0
serves as clock output.
If the system clock prescaler is used, it is the divided system clock that is output when the
CKOUT Fuse is programmed. See “System Clock Prescaler” on page 41. for a description of the
system clock prescaler.
Timer/Counter
Oscillator
For AVR microcontrollers with Timer/Counter Oscillator pins (TOSC1 and TOSC2), the crystal is
connected directly between the pins. The Oscillator provides internal capacitors on TOSC1 and
TOSC2, thereby removing the need for external capacitors. The internal capacitors have a nom-
inal value of 10 pF. The Oscillator is optimized for use with a 32.768 kHz watch crystal. Applying
an external clock source to TOSC1 is not recommended.
System Clock
Prescaler
The ATmega162 system clock can be divided by setting the Clock Prescale Register – CLKPR.
This feature can be used to decrease the system clock frequency and power consumption when
the requirement for processing power is low. This can be used with all clock source options, and
it will affect the clock frequency of the CPU and all synchronous peripherals. clkI/O, clkCPU, and
clkFLASH are divided by a factor as shown in Table 15. Note that the clock frequency of clkASY
(asynchronously Timer/Counter) only will be scaled if the Timer/Counter is clocked
synchronously.
When switching between prescaler settings, the System Clock Prescaler ensures that no
glitches occur in the clock system and that no intermediate frequency is higher than neither the
clock frequency corresponding to the previous setting, nor the clock frequency corresponding to
the new setting.
The ripple counter that implements the prescaler runs at the frequency of the undivided clock,
which may be faster than the CPU’s clock frequency. Hence, it is not possible to determine the
state of the prescaler – even if it were readable, and the exact time it takes to switch from one
clock division to another cannot be exactly predicted.
From the time the CLKPS values are written, it takes between T1 + T2 and T1 + 2*T2 before the
new clock frequency is active. In this interval, 2 active clock edges are produced. Here, T1 is the
previous clock period, and T2 is the period corresponding to the new prescaler setting.
To avoid unintentional changes of clock frequency, a special write procedure must be followed
to change the CLKPS bits:
1. Write the Clock Prescaler Change Enable (CLKPCE) bit to one and all other bits in
CLKPR to zero.
2. Within four cycles, write the desired value to CLKPS while writing a zero to CLKPCE.
Caution: An interrupt between step 1 and step 2 will make the timed sequence fail. It is recom-
mended to have the Global Interrupt Flag cleared during these steps to avoid this problem.
Clock Prescale
Register – CLKPR
• Bit 7 – CLKPCE: Clock Prescaler Change Enable
The CLKPCE bit must be written to logic one to enable change of the CLKPS bits. CLKPCE is
cleared by hardware four cycles after it is written or when CLKPS is written. Setting the CLKPCE
bit will disable interrupts, as explained in the CLKPS description below.
Bit 7 6 5 4 3 2 1 0
CLKPCE – – – CLKPS3 CLKPS2 CLKPS1 CLKPS0 CLKPR
Read/Write R/W R R R R/W R/W R/W R/W
Initial Value 0 0 0 0 See Bit Description
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2513K–AVR–07/09
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• Bits 3..0 – CLKPS3..0: Clock Prescaler Select Bits 3 - 0
These bits define the division factor between the selected clock source and the internal system
clock. These bits can be written run-time to vary the clock frequency to suit the application
requirements. As the divider divides the master clock input to the MCU, the speed of all synchro-
nous peripherals is reduced when a division factor is used. The division factors are given in
Table 15.
The CKDIV8 Fuse determines the initial value of the CLKPS bits. If CKDIV8 is unprogrammed,
the CLKPS bits will be reset to “0000”. If CKDIV8 is programmed, CLKPS bits are reset to
“0011”, giving a division factor of 8 at start up. This feature should be used if the selected clock
source has a higher frequency than the maximum frequency of the device at the present operat-
ing conditions. Note that any value can be written to the CLKPS bits regardless of the CKDIV8
Fuse setting. The Application software must ensure that a sufficient division factor is chosen if
the selected clock source has a higher frequency than the maximum frequency of the device at
the present operating conditions. The device is shipped with the CKDIV8 Fuse programmed.
Table 15. Clock Prescaler Select
CLKPS3 CLKPS2 CLKPS1 CLKPS0 Clock Division Factor
00001
00012
00104
00118
010016
010132
011064
0111128
1000256
1001Reserved
1010Reserved
1011Reserved
1100Reserved
1101Reserved
1110Reserved
1111Reserved
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ATmega162/V
Power
Management
and Sleep
Modes
Sleep modes enable the application to shut down unused modules in the MCU, thereby saving
power. The AVR provides various sleep modes allowing the user to tailor the power consump-
tion to the application’s requirements.
To enter any of the five sleep modes, the SE bit in MCUCR must be written to logic one and a
SLEEP instruction must be executed. The SM2 bit in MCUCSR, the SM1 bit in MCUCR, and the
SM0 bit in the EMCUCR Register select which sleep mode (Idle, Power-down, Power-save,
Standby, or Extended Standby) will be activated by the SLEEP instruction. See Table 16 for a
summary. If an enabled interrupt occurs while the MCU is in a sleep mode, the MCU wakes up.
The MCU is then halted for four cycles in addition to the start-up time, executes the interrupt rou-
tine, and resumes execution from the instruction following SLEEP. The contents of the Register
File and SRAM are unaltered when the device wakes up from sleep. If a Reset occurs during
sleep mode, the MCU wakes up and executes from the Reset Vector.
Figure 18 on page 35 presents the different clock systems in the ATmega162, and their distribu-
tion. The figure is helpful in selecting an appropriate sleep mode.
MCU Control Register
– MCUCR
• Bit 5 – SE: Sleep Enable
The SE bit must be written to logic one to make the MCU enter the sleep mode when the SLEEP
instruction is executed. To avoid the MCU entering the sleep mode unless it is the programmer’s
purpose, it is recommended to write the Sleep Enable (SE) bit to one just before the execution of
the SLEEP instruction and to clear it immediately after waking up.
• Bit 4 – SM1: Sleep Mode Select Bit 1
The Sleep Mode Select bits select between the five available sleep modes as shown in Table
16.
MCU Control and
Status Register –
MCUCSR
• Bit 5 – SM2: Sleep Mode Select Bit 2
The Sleep Mode Select bits select between the five available sleep modes as shown in Table
16.
Bit 76543210
SRE SRW10 SE SM1 ISC11 ISC10 ISC01 ISC00 MCUCR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
JTD –SM2JTRF WDRF BORF EXTRF PORF MCUCSR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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ATmega162/V
Extended MCU
Control Register –
EMCUCR
• Bit 7 – SM0: Sleep Mode Select Bit 0
The Sleep Mode Select bits select between the five available sleep modes as shown in Table
16.
Note: 1. Standby mode and Extended Standby mode are only available with external crystals or
resonators.
Idle Mode When the SM2..0 bits are written to 000, the SLEEP instruction makes the MCU enter Idle
mode, stopping the CPU but allowing the SPI, USART, Analog Comparator, Timer/Counters,
Watchdog, and the interrupt system to continue operating. This sleep mode basically halts
clkCPU and clkFLASH, while allowing the other clocks to run.
Idle mode enables the MCU to wake up from external triggered interrupts as well as internal
ones like the Timer Overflow and USART Transmit Complete interrupts. If wake-up from the
Analog Comparator interrupt is not required, the Analog Comparator can be powered down by
setting the ACD bit in the Analog Comparator Control and Status Register – ACSR. This will
reduce power consumption in Idle mode.
Power-down Mode When the SM2..0 bits are written to 010, the SLEEP instruction makes the MCU enter Power-
down mode. In this mode, the external Oscillator is stopped, while the external interrupts and the
Watchdog continue operating (if enabled). Only an External Reset, a Watchdog Reset, a Brown-
out Reset, an External Level Interrupt on INT0 or INT1, an external interrupt on INT2, or a pin
change interrupt can wake up the MCU. This sleep mode basically halts all generated clocks,
allowing operation of asynchronous modules only.
Note that if a level triggered interrupt is used for wake-up from Power-down mode, the changed
level must be held for some time to wake up the MCU. Refer to “External Interrupts” on page 84
for details.
When waking up from Power-down mode, there is a delay from the wake-up condition occurs
until the wake-up becomes effective. This allows the clock to restart and become stable after
having been stopped. The wake-up period is defined by the same CKSEL Fuses that define the
Reset Time-out period, as described in “Clock Sources” on page 36.
Bit 76543210
SM0 SRL2 SRL1 SRL0 SRW01 SRW00 SRW11 ISC2 EMCUCR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Table 16. Sleep Mode Select
SM2 SM1 SM0 Sleep Mode
000Idle
001Reserved
010Power-down
011Power-save
100Reserved
101Reserved
110Standby
(1)
1 1 1 Extended Standby(1)
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Power-save Mode When the SM2..0 bits are written to 011, the SLEEP instruction makes the MCU enter Power-
save mode. This mode is identical to Power-down, with one exception:
If Timer/Counter2 is clocked asynchronously, i.e., the AS2 bit in ASSR is set, Timer/Counter2
will run during sleep. The device can wake up from either Timer Overflow or Output Compare
event from Timer/Counter2 if the corresponding Timer/Counter2 interrupt enable bits are set in
TIMSK, and the Global Interrupt Enable bit in SREG is set.
If the Asynchronous Timer is NOT clocked asynchronously, Power-down mode is recommended
instead of Power-save mode because the contents of the registers in the Asynchronous Timer
should be considered undefined after wake-up in Power-save mode if AS2 is 0.
This sleep mode basically halts all clocks except clkASY, allowing operation only of asynchronous
modules, including Timer/Counter 2 if clocked asynchronously.
Standby Mode When the SM2..0 bits are 110 and an external crystal/resonator clock option is selected, the
SLEEP instruction makes the MCU enter Standby mode. This mode is identical to Power-down
with the exception that the main Oscillator is kept running. From Standby mode, the device
wakes up in six clock cycles.
Extended Standby
Mode
When the SM2..0 bits are 111 and an external crystal/resonator clock option is selected, the
SLEEP instruction makes the MCU enter Extended Standby mode. This mode is identical to
Power-save mode with the exception that the main Oscillator is kept running. From Extended
Standby mode, the device wakes up in six clock cycles.
Notes: 1. External Crystal or resonator selected as clock source
2. If AS2 bit in ASSR is set
3. For INT1 and INT0, only level interrupt
Table 17. Active Clock domains and Wake up sources in the different sleep modes
Active Clock domains Oscillators Wake-up Sources
Sleep Mode clkCPU clkFLASH clkIO clkASY
Main Clock
Source Enabled
Timer Osc
Enabled
INT2
INT1
INT0
and Pin Change Timer2
SPM/
EEPROM
Ready
Other
I/O
Idle X X X X(2) XXXX
Power-down X(3)
Power-save X(2) X(2) X(3) X(2)
Standby(1) XX
(3)
Extended Standby(1) X(2) XX
(2) X(3) X(2)
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Minimizing Power
Consumption
There are several issues to consider when trying to minimize the power consumption in an AVR
controlled system. In general, sleep modes should be used as much as possible, and the sleep
mode should be selected so that as few as possible of the device’s functions are operating. All
functions not needed should be disabled. In particular, the following modules may need special
consideration when trying to achieve the lowest possible power consumption.
Analog Comparator When entering Idle mode, the Analog Comparator should be disabled if not needed. In the other
sleep modes, the Analog Comparator is automatically disabled. However, if the Analog Compar-
ator is set up to use the Internal Voltage Reference as input, the Analog Comparator should be
disabled in all sleep modes. Otherwise, the Internal Voltage Reference will be enabled, indepen-
dent of sleep mode. Refer to “Analog Comparator” on page 195 for details on how to configure
the Analog Comparator.
Brown-out Detector If the Brown-out Detector is not needed in the application, this module should be turned off. If the
Brown-out Detector is enabled by the BODLEVEL Fuses, it will be enabled in all sleep modes,
and hence, always consume power. In the deeper sleep modes, this will contribute significantly
to the total current consumption. Refer to “Brown-out Detection” on page 50 for details on how to
configure the Brown-out Detector.
Internal Voltage
Reference
The Internal Voltage Reference will be enabled when needed by the Brown-out Detector or the
Analog Comparator. If these modules are disabled as described in the sections above, the inter-
nal voltage reference will be disabled and it will not be consuming power. When turned on again,
the user must allow the reference to start up before the output is used. If the reference is kept on
in sleep mode, the output can be used immediately. Refer to “Internal Voltage Reference” on
page 52 for details on the start-up time.
Watchdog Timer If the Watchdog Timer is not needed in the application, this module should be turned off. If the
Watchdog Timer is enabled, it will be enabled in all sleep modes, and hence, always consume
power. In the deeper sleep modes, this will contribute significantly to the total current consump-
tion. Refer to “Watchdog Timer” on page 52 for details on how to configure the Watchdog Timer.
Port Pins When entering a sleep mode, all port pins should be configured to use minimum power. The
most important thing is to ensure that no pins drive resistive loads. In sleep modes where the I/O
clock (clkI/O) is stopped, the input buffers of the device will be disabled. This ensures that no
power is consumed by the input logic when not needed. In some cases, the input logic is needed
for detecting wake-up conditions, and it will then be enabled. Refer to the section “Digital Input
Enable and Sleep Modes” on page 67 for details on which pins are enabled. If the input buffer is
enabled and the input signal is left floating or have an analog signal level close to VCC/2, the
input buffer will use excessive power.
JTAG Interface and
On-chip Debug
System
If the On-chip debug system is enabled by the OCDEN Fuse and the chip enter Power down or
Power save sleep mode, the main clock source remains enabled. In these sleep modes, this will
contribute significantly to the total current consumption. There are three alternative ways to
avoid this:
• Disable OCDEN Fuse.
• Disable JTAGEN Fuse.
• Write one to the JTD bit in MCUCSR.
The TDO pin is left floating when the JTAG interface is enabled while the JTAG TAP controller is
not shifting data. If the hardware connected to the TDO pin does not pull up the logic level,
power consumption will increase. Note that the TDI pin for the next device in the scan chain con-
tains a pull-up that avoids this problem. Writing the JTD bit in the MCUCSR register to one or
leaving the JTAG fuse unprogrammed disables the JTAG interface.
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2513K–AVR–07/09
ATmega162/V
System Control
and Reset
Resetting the AVR During Reset, all I/O Registers are set to their initial values, and the program starts execution
from the Reset Vector. The instruction placed at the Reset Vector must be a JMP – Absolute
Jump – instruction to the reset handling routine. If the program never enables an interrupt
source, the Interrupt Vectors are not used, and regular program code can be placed at these
locations. This is also the case if the Reset Vector is in the Application section while the Interrupt
Vectors are in the Boot section or vice versa. The circuit diagram in Figure 21 shows the Reset
Logic. Table 18 defines the electrical parameters of the reset circuitry.
The I/O ports of the AVR are immediately reset to their initial state when a reset source goes
active. This does not require any clock source to be running.
After all reset sources have gone inactive, a delay counter is invoked, stretching the Internal
Reset. This allows the power to reach a stable level before normal operation starts. The Time-
out period of the delay counter is defined by the user through the CKSEL Fuses. The different
selections for the delay period are presented in “Clock Sources” on page 36.
Reset Sources The ATmega162 has five sources of reset:
• Power-on Reset. The MCU is reset when the supply voltage is below the Power-on Reset
threshold (VPOT).
• External Reset. The MCU is reset when a low level is present on the RESET pin for longer
than the minimum pulse length.
• Watchdog Reset. The MCU is reset when the Watchdog Timer period expires and the
Watchdog is enabled.
• Brown-out Reset. The MCU is reset when the supply voltage VCC is below the Brown-out
Reset threshold (VBOT) and the Brown-out Detector is enabled. The device is guaranteed to
operate at maximum frequency for the VCC voltage down to VBOT
. VBOT must be set to the
corresponding minimum voltage of the device (i.e., minimum VBOT for ATmega162V is 1.8V).
• JTAG AVR Reset. The MCU is reset as long as there is a logic one in the Reset Register,
one of the scan chains of the JTAG system. Refer to the section “IEEE 1149.1 (JTAG)
Boundary-scan” on page 204 for details.
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2513K–AVR–07/09
ATmega162/V
Figure 21. Reset Logic
Note: 1. The Power-on Reset will not work unless the supply voltage has been below VPOT (falling)
Power-on Reset A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detection level
is defined in Table 18. The POR is activated whenever VCC is below the detection level. The
POR circuit can be used to trigger the Start-up Reset, as well as to detect a failure in supply
voltage.
A Power-on Reset (POR) circuit ensures that the device is Reset from Power-on. Reaching the
Power-on Reset threshold voltage invokes the delay counter, which determines how long the
device is kept in RESET after VCC rise. The RESET signal is activated again, without any delay,
when VCC decreases below the detection level.
Table 18. Reset Characteristics
Symbol Parameter Condition Min. Typ. Max. Units
VPOT
Power-on Reset
Threshold Voltage (rising) TA = -40 - 85°C0.7 1.0 1.4 V
Power-on Reset
Threshold Voltage
(falling)(1)
TA = -40 - 85°C0.6 0.9 1.3 V
VRST
RESET Pin Threshold
Voltage VCC = 3V 0.1 VCC 0.9 VCC V
tRST
Minimum pulse width on
RESET Pin VCC = 3V 2.5 µs
MCU Control and Status
Register (MCUCSR)
BODLEVEL [ 2..0]
Delay Counters
CKSEL[3:0]
CK
TIMEOUT
WDRF
BORF
EXTRF
PORF
DATA BU S
Clock
Generator
SPIKE
FILTER
Pull-up Resistor
JTRF
JTAG Reset
Register
Watchdog
Oscillator
SUT[1:0]
Watchdog
Timer
V
CC
RESET Reset Circuit
Brown-out
Reset Circuit
Power-on
Reset Circuit
COUNTER RESET
INTERNAL RESET
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2513K–AVR–07/09
ATmega162/V
Figure 22. MCU Start-up, RESET Tied to VCC.
Figure 23. MCU Start-up, RESET Extended Externally
External Reset An External Reset is generated by a low level on the RESET pin. Reset pulses longer than the
minimum pulse width (see Table 18) will generate a Reset, even if the clock is not running.
Shorter pulses are not guaranteed to generate a Reset. When the applied signal reaches the
Reset Threshold Voltage – VRST on its positive edge, the delay counter starts the MCU after the
Time-out period tTOUT has expired.
Figure 24. External Reset During Operation
V
RESET
TIME-OUT
INTERNAL
RESET
tTOUT
VPOT
VRST
CC
RESET
TIME-OUT
INTERNAL
RESET
tTOUT
VPOT
VRST
VCC
CC
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ATmega162/V
Brown-out Detection ATmega162 has an On-chip Brown-out Detection (BOD) circuit for monitoring the VCC level dur-
ing operation by comparing it to a fixed trigger level. The trigger level for the BOD can be
selected by the BODLEVEL Fuses. The trigger level has a hysteresis to ensure spike free
Brown-out Detection. The hysteresis on the detection level should be interpreted as VBOT+ =
VBOT + VHYST/2 and VBOT- = VBOT - VHYST/2.
Notes: 1. VBOT may be below nominal minimum operating voltage for some devices. For devices where
this is the case, the device is tested down to VCC = VBOT during the production test. This guar-
antees that a Brown-out Reset will occur before VCC drops to a voltage where correct
operation of the microcontroller is no longer guaranteed. This test is performed using
BODLEVEL = 110 for ATmega162V, BODLEVEL = 101 and BODLEVEL = 100 for
ATmega162.
2. For ATmega162V. Otherwise reserved.
When the BOD is enabled and VCC decreases to a value below the trigger level (VBOT- in Figure
25), the Brown-out Reset is immediately activated. When VCC increases above the trigger level
(VBOT+ in Figure 25), the delay counter starts the MCU after the Time-out period tTOUT has
expired.
The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level for lon-
ger than tBOD given in Table 18.
Table 19. BODLEVEL Fuse Coding
BODLEVEL Fuses [2:0] Min. VBOT(1) Typ. VBOT Max. VBOT Units
111 BOD Disabled
110(2) 1.7 1.8 2.0
V
101 2.5 2.7 2.9
100 4.1 4.3 4.5
011(2) 2.1 2.3 2.5
010
Reserved001
000
Table 20. Brown-out Hysteresis
Symbol Parameter Min. Typ. Max. Units
VHYST Brown-out Detector hysteresis 50 mV
tBOD Min Pulse Width on Brown-out Reset 2 µs
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Figure 25. Brown-out Reset During Operation
Watchdog Reset When the Watchdog times out, it will generate a short reset pulse of one CK cycle duration. On
the falling edge of this pulse, the delay timer starts counting the Time-out period tTOUT. Refer to
page 52 for details on operation of the Watchdog Timer.
Figure 26. Watchdog Reset During Operation
MCU Control and
Status Register –
MCUCSR
The MCU Control and Status Register provides information on which reset source caused an
MCU Reset.
• Bit 4 – JTRF: JTAG Reset Flag
This bit is set if a reset is being caused by a logic one in the JTAG Reset Register selected by
the JTAG instruction AVR_RESET. This bit is reset by a Power-on Reset, or by writing a logic
zero to the flag.
• Bit 3 – WDRF: Watchdog Reset Flag
This bit is set if a Watchdog Reset occurs. The bit is reset by a Power-on Reset, or by writing a
logic zero to the flag.
VCC
RESET
TIME-OUT
INTERNAL
RESET
VBOT-
VBOT+
tTOUT
CK
CC
Bit 76543210
JTD –SM2 JTRF WDRF BORF EXTRF PORF MCUCSR
Read/Write R/W R/W R R/W R/W R/W R/W R/W
Initial Value 0 0 0 See Bit Description
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2513K–AVR–07/09
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• Bit 2 – BORF: Brown-out Reset Flag
This bit is set if a Brown-out Reset occurs. The bit is reset by a Power-on Reset, or by writing a
logic zero to the flag.
• Bit 1 – EXTRF: External Reset Flag
This bit is set if an External Reset occurs. The bit is reset by a Power-on Reset, or by writing a
logic zero to the flag.
• Bit 0 – PORF: Power-on Reset Flag
This bit is set if a Power-on Reset occurs. The bit is reset only by writing a logic zero to the flag.
To make use of the Reset Flags to identify a reset condition, the user should read and then
Reset the MCUCSR as early as possible in the program. If the register is cleared before another
reset occurs, the source of the Reset can be found by examining the Reset Flags.
Internal Voltage
Reference
ATmega162 features an internal bandgap reference. This reference is used for Brown-out
Detection, and it can be used as an input to the Analog Comparator.
Voltage Reference
Enable Signals and
Start-up Time
The voltage reference has a start-up time that may influence the way it should be used. The
start-up time is given in Table 21. To save power, the reference is not always turned on. The ref-
erence is on during the following situations:
1. When the BOD is enabled (by programming the BODLEVEL Fuses).
2. When the bandgap reference is connected to the Analog Comparator (by setting the
ACBG bit in ACSR).
Thus, when the BOD is not enabled, after setting the ACBG bit, the user must always allow the
reference to start up before the output from the Analog Comparator is used. To reduce power
consumption in Power-down mode, the user can avoid the two conditions above to ensure that
the reference is turned off before entering Power-down mode.
Watchdog Timer The Watchdog Timer is clocked from a separate On-chip Oscillator which runs at 1 MHz. This is
the typical frequency at VCC = 5V. See characterization data for typical values at other VCC lev-
els. By controlling the Watchdog Timer prescaler, the Watchdog Reset interval can be adjusted
as shown in Table 23 on page 54. The WDR – Watchdog Reset – instruction resets the Watch-
dog Timer. The Watchdog Timer is also reset when it is disabled and when a Chip Reset occurs.
Eight different clock cycle periods can be selected to determine the reset period. If the reset
period expires without another Watchdog Reset, the ATmega162 resets and executes from the
Reset Vector. For timing details on the Watchdog Reset, refer to page 54.
To prevent unintentional disabling of the Watchdog or unintentional change of time-out period, 3
different safety levels are selected by the Fuses M161C and WDTON as shown in Table 22.
Safety level 0 corresponds to the setting in ATmega161. There is no restriction on enabling the
Table 21. Internal Voltage Reference Characteristics
Symbol Parameter Min. Typ. Max. Units
VBG Bandgap reference voltage 1.05 1.10 1.15 V
tBG Bandgap reference start-up time 40 70 µs
IBG
Bandgap reference current
consumption 10 µA
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2513K–AVR–07/09
ATmega162/V
WDT in any of the safety levels. Refer to “Timed Sequences for Changing the Configuration of
the Watchdog Timer” on page 56 for details.
Figure 27. Watchdog Timer
Watchdog Timer
Control Register –
WDTCR
• Bits 7..5 – Res: Reserved Bits
These bits are reserved bits in the ATmega162 and will always read as zero.
• Bit 4 – WDCE: Watchdog Change Enable
This bit must be set when the WDE bit is written to logic zero. Otherwise, the Watchdog will not
be disabled. Once written to one, hardware will clear this bit after four clock cycles. Refer to the
description of the WDE bit for a Watchdog disable procedure. In Safety Levels 1 and 2, this bit
must also be set when changing the prescaler bits. See “Timed Sequences for Changing the
Configuration of the Watchdog Timer” on page 56.
• Bit 3 – WDE: Watchdog Enable
When the WDE is written to logic one, the Watchdog Timer is enabled, and if the WDE is written
to logic zero, the Watchdog Timer function is disabled. WDE can only be cleared if the WDCE bit
has logic level one. To disable an enabled Watchdog Timer, the following procedure must be
followed:
Table 22. WDT Configuration as a Function of the Fuse Settings of M161C and WDTON.
M161C WDTON
Safety
Level
WDT
Initial
State
How to Disable
the WDT
How to
Change Time-
out
Unprogrammed Unprogrammed 1 Disabled Timed sequence Timed
sequence
Unprogrammed Programmed 2 Enabled Always enabled Timed
sequence
Programmed Unprogrammed 0 Disabled Timed sequence No restriction
Programmed Programmed 2 Enabled Always enabled Timed
sequence
WATCHDOG
OSCILLATOR
Bit 76543210
– – – WDCE WDE WDP2 WDP1 WDP0 WDTCR
Read/Write R R R R/W R/W R/W R/W R/W
Initial Value00000000
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2513K–AVR–07/09
ATmega162/V
1. In the same operation, write a logic one to WDCE and WDE. A logic one must be written
to WDE even though it is set to one before the disable operation starts.
2. Within the next four clock cycles, write a logic 0 to WDE. This disables the Watchdog.
In safety level 2, it is not possible to disable the Watchdog Timer, even with the algorithm
described above. See “Timed Sequences for Changing the Configuration of the Watchdog
Timer” on page 56.
• Bits 2..0 – WDP2, WDP1, WDP0: Watchdog Timer Prescaler 2, 1, and 0
The WDP2, WDP1, and WDP0 bits determine the Watchdog Timer prescaling when the Watch-
dog Timer is enabled. The different prescaling values and their corresponding Timeout Periods
are shown in Table 23.
Table 23. Watchdog Timer Prescale Select
WDP2 WDP1 WDP0
Number of WDT
Oscillator Cycles
Typical Time-out
at VCC = 3.0V
Typical Time-out
at VCC = 5.0V
0 0 0 16K (16,384) 17 ms 16 ms
0 0 1 32K (32,768) 34 ms 33 ms
0 1 0 65K (65,536) 69 ms 65 ms
0 1 1 128K (131,072) 0.14 s 0.13 s
1 0 0 256K (262,144) 0.27 s 0.26 s
1 0 1 512K (524,288) 0.55 s 0.52 s
1 1 0 1,024K (1,048,576) 1.1 s 1.0 s
1 1 1 2,048K (2,097,152) 2.2 s 2.1 s
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The following code example shows one assembly and one C function for turning off the WDT.
The example assumes that interrupts are controlled (e.g., by disabling interrupts globally) so that
no interrupts will occur during execution of these functions.
Assembly Code Example
WDT_off:
; Reset WDT
WDR
; Write logical one to W?CE and WDE
in r16, WDTCR
ori r16, (1<<WDCE)|(1<<WDE)
out WDTCR, r16
; Turn off WDT
ldi r16, (0<<WDE)
out WDTCR, r16
ret
C Code Example
void WDT_off(void)
{
/* Reset WDT*/
_WDR()
/* Write logical on? to WDCE and WDE */
WDTCR |= (1<<WDCE) | (1<?WDE);
/* Turn off WDT */
WDTCR = 0x00;
}
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2513K–AVR–07/09
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Timed Sequences
for Changing the
Configuration of
the Watchdog
Timer
The sequence for changing configuration differs slightly between the three safety levels. Sepa-
rate procedures are described for each level.
Safety Level 0 This mode is compatible with the Watchdog operation found in ATmega161. The Watchdog
Timer is initially disabled, but can be enabled by writing the WDE bit to one without any restric-
tion. The Time-out period can be changed at any time without restriction. To disable an enabled
Watchdog Timer, the procedure described on page 53 (WDE bit description) must be followed.
Safety Level 1 In this mode, the Watchdog Timer is initially disabled, but can be enabled by writing the WDE bit
to one without any restriction. A timed sequence is needed when changing the Watchdog Time-
out period or disabling an enabled Watchdog Timer. To disable an enabled Watchdog Timer,
and/or changing the Watchdog Time-out, the following procedure must be followed:
1. In the same operation, write a logic one to WDCE and WDE. A logic one must be written
to WDE regardless of the previous value of the WDE bit.
2. Within the next four clock cycles, in the same operation, write the WDE and WDP bits as
desired, but with the WDCE bit cleared.
Safety Level 2 In this mode, the Watchdog Timer is always enabled, and the WDE bit will always read as one. A
timed sequence is needed when changing the Watchdog Time-out period. To change the
Watchdog Time-out, the following procedure must be followed:
1. In the same operation, write a logical one to WDCE and WDE. Even though the WDE
always is set, the WDE must be written to one to start the timed sequence.
2. Within the next four clock cycles, in the same operation, write the WDP bits as desired,
but with the WDCE bit cleared. The value written to the WDE bit is irrelevant.
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2513K–AVR–07/09
ATmega162/V
Interrupts This section describes the specifics of the interrupt handling as performed in ATmega162. For a
general explanation of the AVR interrupt handling, refer to “Reset and Interrupt Handling” on
page 14. Table 24 shows the interrupt table when the compatibility fuse (M161C) is unpro-
grammed, while Table 25 shows the interrupt table when M161C Fuse is programmed. All
assembly code examples in this sections are using the interrupt table when the M161C Fuse is
unprogrammed.
Interrupt Vectors
in ATmega162 Table 24. Reset and Interrupt Vectors if M161C is unprogrammed
Vector No.
Program
Address(2) Source Interrupt Definition
10x000
(1) RESET External Pin, Power-on Reset, Brown-out
Reset, Watchdog Reset, and JTAG AVR
Reset
2 0x002 INT0 External Interrupt Request 0
3 0x004 INT1 External Interrupt Request 1
4 0x006 INT2 External Interrupt Request 2
5 0x008 PCINT0 Pin Change Interrupt Request 0
6 0x00A PCINT1 Pin Change Interrupt Request 1
7 0x00C TIMER3 CAPT Timer/Counter3 Capture Event
8 0x00E TIMER3 COMPA Timer/Counter3 Compare Match A
9 0x010 TIMER3 COMPB Timer/Counter3 Compare Match B
10 0x012 TIMER3 OVF Timer/Counter3 Overflow
11 0x014 TIMER2 COMP Timer/Counter2 Compare Match
12 0x016 TIMER2 OVF Timer/Counter2 Overflow
13 0x018 TIMER1 CAPT Timer/Counter1 Capture Event
14 0x01A TIMER1 COMPA Timer/Counter1 Compare Match A
15 0x01C TIMER1 COMPB Timer/Counter1 Compare Match B
16 0x01E TIMER1 OVF Timer/Counter1 Overflow
17 0x020 TIMER0 COMP Timer/Counter0 Compare Match
18 0x022 TIMER0 OVF Timer/Counter0 Overflow
19 0x024 SPI, STC Serial Transfer Complete
20 0x026 USART0, RXC USART0, Rx Complete
21 0x028 USART1, RXC USART1, Rx Complete
22 0x02A USART0, UDRE USART0 Data Register Empty
23 0x02C USART1, UDRE USART1 Data Register Empty
24 0x02E USART0, TXC USART0, Tx Complete
25 0x030 USART1, TXC USART1, Tx Complete
26 0x032 EE_RDY EEPROM Ready
27 0x034 ANA_COMP Analog Comparator
28 0x036 SPM_RDY Store Program Memory Ready
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Notes: 1. When the BOOTRST Fuse is programmed, the device will jump to the Boot Loader address at
reset, see “Boot Loader Support – Read-While-Write Self-programming” on page 217.
2. When the IVSEL bit in GICR is set, Interrupt Vectors will be moved to the start of the Boot
Flash section. The address of each Interrupt Vector will then be the address in this table added
to the start address of the Boot Flash section.
Notes: 1. When the BOOTRST Fuse is programmed, the device will jump to the Boot Loader address at
reset, see “Boot Loader Support – Read-While-Write Self-programming” on page 217.
2. When the IVSEL bit in GICR is set, Interrupt Vectors will be moved to the start of the Boot
Flash section. The address of each Interrupt Vector will then be the address in this table added
to the start address of the Boot Flash section.
Table 25. Reset and Interrupt Vectors if M161C is programmed
Vector No.
Program
Address(2) Source Interrupt Definition
10x000
(1) RESET External Pin, Power-on Reset, Brown-out
Reset, Watchdog Reset, and JTAG AVR
Reset
2 0x002 INT0 External Interrupt Request 0
3 0x004 INT1 External Interrupt Request 1
4 0x006 INT2 External Interrupt Request 2
5 0x008 TIMER2 COMP Timer/Counter2 Compare Match
6 0x00A TIMER2 OVF Timer/Counter2 Overflow
7 0x00C TIMER1 CAPT Timer/Counter1 Capture Event
8 0x00E TIMER1 COMPA Timer/Counter1 Compare Match A
9 0x010 TIMER1 COMPB Timer/Counter1 Compare Match B
10 0x012 TIMER1 OVF Timer/Counter1 Overflow
11 0x014 TIMER0 COMP Timer/Counter0 Compare Match
12 0x016 TIMER0 OVF Timer/Counter0 Overflow
13 0x018 SPI, STC Serial Transfer Complete
14 0x01A USART0, RXC USART0, Rx Complete
15 0x01C USART1, RXC USART1, Rx Complete
16 0x01E USART0, UDRE USART0 Data Register Empty
17 0x020 USART1, UDRE USART1 Data Register Empty
18 0x022 USART0, TXC USART0, Tx Complete
19 0x024 USART1, TXC USART1, Tx Complete
20 0x026 EE_RDY EEPROM Ready
21 0x028 ANA_COMP Analog Comparator
22 0x02A SPM_RDY Store Program Memory Ready
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Table 26 shows Reset and Interrupt Vectors placement for the various combinations of
BOOTRST and IVSEL settings. If the program never enables an interrupt source, the Interrupt
Vectors are not used, and regular program code can be placed at these locations. This is also
the case if the Reset Vector is in the Application section while the Interrupt Vectors are in the
Boot section or vice versa.
Note: 1. The Boot Reset Address is shown in Table 93 on page 228. For the BOOTRST Fuse “1”
means unprogrammed while “0” means programmed.
The most typical and general program setup for the Reset and Interrupt Vector Addresses in
ATmega162 is:
Address Labels Code Comments
0x000 jmp RESET ; Reset Handler
0x002 jmp EXT_INT0 ; IRQ0 Handler
0x004 jmp EXT_INT1 ; IRQ1 Handler
0x006 jmp EXT_INT2 ; IRQ2 Handler
0x008 jmp PCINT0 ; PCINT0 Handler
0x00A jmp PCINT1 ; PCINT1 Handler
0x00C jmp TIM3_CAPT ; Timer3 Capture Handler
0x00E jmp TIM3_COMPA ; Timer3 CompareA Handler
0x010 jmp TIM3_COMPB ; Timer3 CompareB Handler
0x012 jmp TIM3_OVF ; Timer3 Overflow Handler
0x014 jmp TIM2_COMP ; Timer2 Compare Handler
0x016 jmp TIM2_OVF ; Timer2 Overflow Handler
0x018 jmp TIM1_CAPT ; Timer1 Capture Handler
0x01A jmp TIM1_COMPA ; Timer1 CompareA Handler
0x01C jmp TIM1_COMPB ; Timer1 CompareB Handler
0x01E jmp TIM1_OVF ; Timer1 Overflow Handler
0x020 jmp TIM0_COMP ; Timer0 Compare Handler
0x022 jmp TIM0_OVF ; Timer0 Overflow Handler
0x024 jmp SPI_STC ; SPI Transfer Complete Handler
0x026 jmp USART0_RXC ; USART0 RX Complete Handler
0x028 jmp USART1_RXC ; USART1 RX Complete Handler
0x02A jmp USART0_UDRE ; UDR0 Empty Handler
0x02C jmp USART1_UDRE ; UDR1 Empty Handler
0x02E jmp USART0_TXC ; USART0 TX Complete Handler
0x030 jmp USART1_TXC ; USART1 TX Complete Handler
0x032 jmp EE_RDY ; EEPROM Ready Handler
0x034 jmp ANA_COMP ; Analog Comparator Handler
0x036 jmp SPM_RDY ; Store Program Memory Ready Handler
;
0x038 RESET: ldi r16,high(RAMEND) ; Main program start
0x039 out SPH,r16 ; Set Stack Pointer to top of RAM
Table 26. Reset and Interrupt Vectors Placement(1)
BOOTRST IVSEL Reset address Interrupt Vectors Start Address
1 0 0x0000 0x0002
1 1 0x0000 Boot Reset Address + 0x0002
0 0 Boot Reset Address 0x0002
0 1 Boot Reset Address Boot Reset Address + 0x0002
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0x03A ldi r16,low(RAMEND)
0x03B out SPL,r16
0x03C sei ; Enable interrupts
0x03D <instr> xxx
... ... ...
When the BOOTRST Fuse is unprogrammed, the boot section size set to 2K bytes and the
IVSEL bit in the GICR Register is set before any interrupts are enabled, the most typical and
general program setup for the Reset and Interrupt Vector Addresses is:
Address Labels Code Comments
0x000 RESET: ldi r16,high(RAMEND) ; Main program start
0x001 out SPH,r16 ; Set Stack Pointer to top of RAM
0x002 ldi r16,low(RAMEND)
0x003 out SPL,r16
0x004 sei ; Enable interrupts
0x005 <instr> xxx
;
.org 0x1C02
0x1C02 jmp EXT_INT0 ; IRQ0 Handler
0x1C04 jmp EXT_INT1 ; IRQ1 Handler
... .... .. ;
0x1C36 jmp SPM_RDY ; Store Program Memory Ready Handler
When the BOOTRST Fuse is programmed and the boot section size set to 2K bytes, the most
typical and general program setup for the Reset and Interrupt Vector Addresses is:
Address Labels Code Comments
.org 0x002
0x002 jmp EXT_INT0 ; IRQ0 Handler
0x004 jmp EXT_INT1 ; IRQ1 Handler
... .... .. ;
0x036 jmp SPM_RDY ; Store Program Memory Ready Handler
;
.org 0x1C00
0x1C00 RESET: ldi r16,high(RAMEND) ; Main program start
0x1C01 out SPH,r16 ; Set Stack Pointer to top of RAM
0x1C02 ldi r16,low(RAMEND)
0x1C03 out SPL,r16
0x1C04 sei ; Enable interrupts
0x1C05 <instr> xxx
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When the BOOTRST Fuse is programmed, the boot section size set to 2K bytes and the IVSEL
bit in the GICR Register is set before any interrupts are enabled, the most typical and general
program setup for the Reset and Interrupt Vector Addresses is:
Address Labels Code Comments
.org 0x1C00
0x1C00 jmp RESET ; Reset handler
0x1C02 jmp EXT_INT0 ; IRQ0 Handler
0x1C04 jmp EXT_INT1 ; IRQ1 Handler
... .... .. ;
0x1C36 jmp SPM_RDY ; Store Program Memory Ready Handler
;
0x1C38 RESET: ldi r16,high(RAMEND) ; Main program start
0x1C39 out SPH,r16 ; Set Stack Pointer to top of RAM
0x1C3A ldi r16,low(RAMEND)
0x1C3B out SPL,r16
0x1C3C sei ; Enable interrupts
0x1C3D <instr> xxx
Moving Interrupts
Between Application
and Boot Space
The General Interrupt Control Register controls the placement of the Interrupt Vector table.
General Interrupt
Control Register –
GICR
• Bit 1 – IVSEL: Interrupt Vector Select
When the IVSEL bit is cleared (zero), the Interrupt Vectors are placed at the start of the Flash
memory. When this bit is set (one), the Interrupt Vectors are moved to the beginning of the Boot
Loader section of the Flash. The actual address of the start of the Boot Flash section is deter-
mined by the BOOTSZ Fuses. Refer to the section “Boot Loader Support – Read-While-Write
Self-programming” on page 217 for details. To avoid unintentional changes of Interrupt Vector
tables, a special write procedure must be followed to change the IVSEL bit:
1. Write the Interrupt Vector Change Enable (IVCE) bit to one.
2. Within four cycles, write the desired value to IVSEL while writing a zero to IVCE.
Interrupts will automatically be disabled while this sequence is executed. Interrupts are disabled
in the cycle IVCE is set, and they remain disabled until after the instruction following the write to
IVSEL. If IVSEL is not written, interrupts remain disabled for four cycles. The I-bit in the Status
Register is unaffected by the automatic disabling.
Note: If Interrupt Vectors are placed in the Boot Loader section and Boot Lock bit BLB02 is programmed,
interrupts are disabled while executing from the Application section. If Interrupt Vectors are placed
in the Application section and Boot Lock bit BLB12 is programed, interrupts are disabled while
executing from the Boot Loader section. Refer to the section “Boot Loader Support – Read-While-
Write Self-programming” on page 217 for details on Boot Lock bits.
Bit 76543210
INT1 INT0 INT2 PCIE1 PCIE0 – IVSEL IVCE GICR
Read/Write R/W R/W R/W R/W R/W R R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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• Bit 0 – IVCE: Interrupt Vector Change Enable
The IVCE bit must be written to logic one to enable change of the IVSEL bit. IVCE is cleared by
hardware four cycles after it is written or when IVSEL is written. Setting the IVCE bit will disable
interrupts, as explained in the IVSEL description above. See Code Example below.
Assembly Code Example
Move_interrupts:
; Enable change of Inter?upt Vectors
ldi r16, (1<<IVCE)
out GICR, r16
; Move interrupts to Boo? Flash section
ldi r16, (1<<IVSEL)
out GICR, r16
ret
C Code Example
void Move_interrupts(void)
{
/* Enable change of?Interrupt Vectors */
GICR = (1<<IVCE);
/* Move interrupts to Bo?t Flash section */
GICR = (1<<IVSEL);
}
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I/O-Ports
Introduction All AVR ports have true Read-Modify-Write functionality when used as general digital I/O ports.
This means that the direction of one port pin can be changed without unintentionally changing
the direction of any other pin with the SBI and CBI instructions. The same applies when chang-
ing drive value (if configured as output) or enabling/disabling of pull-up resistors (if configured as
input). Each output buffer has symmetrical drive characteristics with both high sink and source
capability. The pin driver is strong enough to drive LED displays directly. All port pins have indi-
vidually selectable pull-up resistors with a supply-voltage invariant resistance. All I/O pins have
protection diodes to both VCC and Ground as indicated in Figure 28. Refer to “Electrical Charac-
teristics” on page 264 for a complete list of parameters.
Figure 28. I/O Pin Equivalent Schematic
All registers and bit references in this section are written in general form. A lower case “x” repre-
sents the numbering letter for the port, and a lower case “n” represents the bit number. However,
when using the register or bit defines in a program, the precise form must be used. For example,
PORTB3 for bit no. 3 in Port B, here documented generally as PORTxn. The physical I/O Regis-
ters and bit locations are listed in “Register Description for I/O-Ports” on page 82.
Three I/O memory address locations are allocated for each port, one each for the Data Register
– PORTx, Data Direction Register – DDRx, and the Port Input Pins – PINx. The Port Input Pins
I/O location is read only, while the Data Register and the Data Direction Register are read/write.
In addition, the Pull-up Disable – PUD bit in SFIOR disables the pull-up function for all pins in all
ports when set.
Using the I/O port as General Digital I/O is described in “Ports as General Digital I/O” on page
63. Most port pins are multiplexed with alternate functions for the peripheral features on the
device. How each alternate function interferes with the port pin is described in “Alternate Port
Functions” on page 68. Refer to the individual module sections for a full description of the alter-
nate functions.
Note that enabling the alternate function of some of the port pins does not affect the use of the
other pins in the port as general digital I/O.
Ports as General
Digital I/O
The ports are bi-directional I/O ports with optional internal pull-ups. Figure 29 shows a functional
description of one I/O-port pin, here generically called Pxn.
Cpin
Logic
Rpu
See figure
"General Digital I/O" for
details
Pxn
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ATmega162/V
Figure 29. General Digital I/O(1)
Note: 1. WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O, SLEEP,
and PUD are common to all ports.
Configuring the Pin Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown in “Register
Description for I/O-Ports” on page 82, the DDxn bits are accessed at the DDRx I/O address, the
PORTxn bits at the PORTx I/O address, and the PINxn bits at the PINx I/O address.
The DDxn bit in the DDRx Register selects the direction of this pin. If DDxn is written logic one,
Pxn is configured as an output pin. If DDxn is written logic zero, Pxn is configured as an input
pin.
If PORTxn is written logic one when the pin is configured as an input pin, the pull-up resistor is
activated. To switch the pull-up resistor off, PORTxn has to be written logic zero or the pin has to
be configured as an output pin. The port pins are tri-stated when a reset condition becomes
active, even if no clocks are running.
If PORTxn is written logic one when the pin is configured as an output pin, the port pin is driven
high (one). If PORTxn is written logic zero when the pin is configured as an output pin, the port
pin is driven low (zero).
When switching between tri-state ({DDxn, PORTxn} = 0b00) and output high ({DDxn, PORTxn}
= 0b11), an intermediate state with either pull-up enabled ({DDxn, PORTxn} = 0b01) or output
low ({DDxn, PORTxn} = 0b10) must occur. Normally, the pull-up enabled state is fully accept-
able, as a high-impedant environment will not notice the difference between a strong high driver
and a pull-up. If this is not the case, the PUD bit in the SFIOR Register can be set to disable all
pull-ups in all ports.
clk
RPx
RRx
WRx
RDx
WDx
PUD
SYNCHRONIZER
WDx: WRITE DDRx
WRx: WRITE PORTx
RRx: READ PORTx REGISTER
RPx: READ PORTx PIN
PUD: PULLUP DISABLE
clk
I/O
: I/O CLOCK
RDx: READ DDRx
D
L
Q
Q
RESET
RESET
Q
Q
D
Q
QD
CLR
PORTxn
Q
QD
CLR
DDxn
PINxn
DATA BUS
SLEEP
SLEEP: SLEEP CONTROL
Pxn
I/O
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Switching between input with pull-up and output low generates the same problem. The user
must use either the tri-state ({DDxn, PORTxn} = 0b00) or the output high state ({DDxn, PORTxn}
= 0b11) as an intermediate step.
Table 27 summarizes the control signals for the pin value.
Reading the Pin Value Independent of the setting of Data Direction bit DDxn, the port pin can be read through the
PINxn Register bit. As shown in Figure 29, the PINxn Register bit and the preceding latch consti-
tute a synchronizer. This is needed to avoid metastability if the physical pin changes value near
the edge of the internal clock, but it also introduces a delay. Figure 30 shows a timing diagram of
the synchronization when reading an externally applied pin value. The maximum and minimum
propagation delays are denoted tpd,max and tpd,min respectively.
Figure 30. Synchronization when Reading an Externally Applied Pin Value
Table 27. Port Pin Configurations
DDxn PORTxn
PUD
(in SFIOR) I/O Pull-up Comment
0 0 X Input No Tri-state (Hi-Z)
0 1 0 Input Yes
Pxn will source current if ext. pulled
low.
0 1 1 Input No Tri-state (Hi-Z)
1 0 X Output No Output Low (Sink)
1 1 X Output No Output High (Source)
XXX in r17, PINx
0x00 0xFF
INSTRUCTIONS
SYNC LATCH
PINxn
r17
XXX
SYSTEM CLK
tpd, max
tpd, min
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Consider the clock period starting shortly after the first falling edge of the system clock. The latch
is closed when the clock is low, and goes transparent when the clock is high, as indicated by the
shaded region of the “SYNC LATCH” signal. The signal value is latched when the system clock
goes low. It is clocked into the PINxn Register at the succeeding positive clock edge. As indi-
cated by the two arrows tpd,max and tpd,min, a single signal transition on the pin will be delayed
between ½ and 1½ system clock period depending upon the time of assertion.
When reading back a software assigned pin value, a nop instruction must be inserted as indi-
cated in Figure 31. The out instruction sets the “SYNC LATCH” signal at the positive edge of the
clock. In this case, the delay tpd through the synchronizer is one system clock period.
Figure 31. Synchronization when Reading a Software Assigned Pin Value
out PORTx, r16 nop in r17, PINx
0xFF
0x00 0xFF
SYSTEM CLK
r16
INSTRUCTIONS
SYNC LATCH
PINxn
r17
t
pd
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The following code example shows how to set port B pins 0 and 1 high, 2 and 3 low, and define
the port pins from 4 to 7 as input with pull-ups assigned to port pins 6 and 7. The resulting pin
values are read back again, but as previously discussed, a nop instruction is included to be able
to read back the value recently assigned to some of the pins.
Note: 1. For the assembly program, two temporary registers are used to minimize the time from pull-
ups are set on pins 0, 1, 6, and 7, until the direction bits are correctly set, defining bit 2 and 3
as low and redefining bits 0 and 1 as strong high drivers.
Digital Input Enable
and Sleep Modes
As shown in Figure 29, the digital input signal can be clamped to ground at the input of the
Schmitt Trigger. The signal denoted SLEEP in the figure, is set by the MCU Sleep Controller in
Power-down mode, Power-save mode, Standby mode, and Extended Standby mode to avoid
high power consumption if some input signals are left floating, or have an analog signal level
close to VCC/2.
SLEEP is overridden for port pins enabled as External Interrupt pins. If the External Interrupt
Request is not enabled, SLEEP is active also for these pins. SLEEP is also overridden by vari-
ous other alternate functions as described in “Alternate Port Functions” on page 68.
If a logic high level (“one”) is present on an Asynchronous External Interrupt pin configured as
“Interrupt on Rising Edge, Falling Edge, or Any Logic Change on Pin” while the external interrupt
is not enabled, the corresponding External Interrupt Flag will be set when resuming from the
above mentioned sleep modes, as the clamping in these sleep modes produces the requested
logic change.
Assembly Code Example(1)
...
; Define pull-ups a?d set outputs high
; Define directions?for port pins
ldi r16,(1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0)
ldi r17,(1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0)
out PORTB,r16
out DDRB,r17
; Insert nop for sy?chronization
nop
; Read port pins
in r16,PINB
...
C Code Example(1)
unsigned char i;
...
/* Define pull-ups ?nd set outputs high */
/* Define direction? for port pins */
PORTB = (1<<PB7)|(1<<PB6?|(1<<PB1)|(1<<PB0);
DDRB = (1<<DDB3)|(1<<DDB?)|(1<<DDB1)|(1<<DDB0);
/* Insert nop for s?nchronization*/
_NOP();
/* Read port pins */
i = PINB;
...
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Unconnected pins If some pins are unused, it is recommended to ensure that these pins have a defined level. Even
though most of the digital inputs are disabled in the deep sleep modes as described above, float-
ing inputs should be avoided to reduce current consumption in all other modes where the digital
inputs are enabled (Reset, Active mode and Idle mode).
The simplest method to ensure a defined level of an unused pin, is to enable the internal pull-up.
In this case, the pull-up will be disabled during reset. If low power consumption during reset is
important, it is recommended to use an external pull-up or pull-down. Connecting unused pins
directly to VCC or GND is not recommended, since this may cause excessive currents if the pin is
accidentally configured as an output.
Alternate Port
Functions
Most port pins have alternate functions in addition to being general digital I/Os. Figure 32 shows
how the port pin control signals from the simplified Figure 29 can be overridden by alternate
functions. The overriding signals may not be present in all port pins, but the figure serves as a
generic description applicable to all port pins in the AVR microcontroller family.
Figure 32. Alternate Port Functions(1)
Note: 1. WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O, SLEEP,
and PUD are common to all ports. All other signals are unique for each pin.
clk
RPx
RRx
WRx
RDx
WDx
PUD
SYNCHRONIZER
WDx: WRITE DDRx
WRx: WRITE PORTx
RRx: READ PORTx REGISTER
RPx: READ PORTx PIN
PUD: PULLUP DISABLE
clk
I/O
: I/O CLOCK
RDx: READ DDRx
D
L
Q
Q
SET
CLR
0
1
0
1
0
1
DIxn
AIOxn
DIEOExn
PVOVxn
PVOExn
DDOVxn
DDOExn
PUOExn
PUOVxn
PUOExn: Pxn PULL-UP OVERRIDE ENABLE
PUOVxn: Pxn PULL-UP OVERRIDE VALUE
DDOExn: Pxn DATA DIRECTION OVERRIDE ENABLE
DDOVxn: Pxn DATA DIRECTION OVERRIDE VALUE
PVOExn: Pxn PORT VALUE OVERRIDE ENABLE
PVOVxn: Pxn PORT VALUE OVERRIDE VALUE
DIxn: DIGITAL INPUT PIN n ON PORTx
AIOxn: ANALOG INPUT/OUTPUT PIN n ON PORTx
RESET
RESET
Q
QD
CLR
Q
Q D
CLR
Q
Q
D
CLR
PINxn
PORTxn
DDxn
DATA BUS
0
1
DIEOVxn
SLEEP
DIEOExn: Pxn DIGITAL INPUT-ENABLE OVERRIDE ENABLE
DIEOVxn: Pxn DIGITAL INPUT-ENABLE OVERRIDE VALUE
SLEEP: SLEEP CONTROL
Pxn
I/O
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Table 28 summarizes the function of the overriding signals. The pin and port indexes from Fig-
ure 32 are not shown in the succeeding tables. The overriding signals are generated internally in
the modules having the alternate function.
The following subsections shortly describe the alternate functions for each port, and relate the
overriding signals to the alternate function. Refer to the alternate function description for further
details.
Table 28. Generic Description of Overriding Signals for Alternate Functions.
Signal Name Full Name Description
PUOE Pull-up Override
Enable
If this signal is set, the pull-up enable is controlled by the
PUOV signal. If this signal is cleared, the pull-up is
enabled when {DDxn, PORTxn, PUD} = 0b010.
PUOV Pull-up Override
Value
If PUOE is set, the pull-up is enabled/disabled when
PUOV is set/cleared, regardless of the setting of the
DDxn, PORTxn, and PUD Register bits.
DDOE Data Direction
Override Enable
If this signal is set, the Output Driver Enable is controlled
by the DDOV signal. If this signal is cleared, the Output
driver is enabled by the DDxn Register bit.
DDOV Data Direction
Override Value
If DDOE is set, the Output Driver is enabled/disabled
when DDOV is set/cleared, regardless of the setting of the
DDxn Register bit.
PVOE Port Value
Override Enable
If this signal is set and the Output Driver is enabled, the
port value is controlled by the PVOV signal. If PVOE is
cleared, and the Output Driver is enabled, the port Value is
controlled by the PORTxn Register bit.
PVOV Port Value
Override Value
If PVOE is set, the port value is set to PVOV, regardless of
the setting of the PORTxn Register bit.
DIEOE Digital Input
Enable Override
Enable
If this bit is set, the Digital Input Enable is controlled by the
DIEOV signal. If this signal is cleared, the Digital Input
Enable is determined by MCU state (Normal Mode, Sleep
Modes).
DIEOV Digital Input
Enable Override
Value
If DIEOE is set, the Digital Input is enabled/disabled when
DIEOV is set/cleared, regardless of the MCU state
(Normal Mode, Sleep Modes).
DI Digital Input This is the Digital Input to alternate functions. In the figure,
the signal is connected to the output of the schmitt trigger
but before the synchronizer. Unless the Digital Input is
used as a clock source, the module with the alternate
function will use its own synchronizer.
AIO Analog
Input/output
This is the Analog Input/output to/from alternate functions.
The signal is connected directly to the pad, and can be
used bi-directionally.
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Special Function IO
Register – SFIOR
• Bit 2 – PUD: Pull-up Disable
When this bit is written to one, the pull-ups in the I/O ports are disabled even if the DDxn and
PORTxn Registers are configured to enable the pull-ups ({DDxn, PORTxn} = 0b01). See “Con-
figuring the Pin” on page 64 for more details about this feature.
Alternate Functions of
Port A
Port A has an alternate function as the address low byte and data lines for the External Memory
Interface and as Pin Change Interrupt.
Table 30 and Table 31 relate the alternate functions of Port A to the overriding signals shown in
Figure 32 on page 68.
Bit 7 6 5 4 3 2 1 0
TSM XMBK XMM2 XMM1 XMM0 PUD PSR2 PSR310 SFIOR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Table 29. Port A Pins Alternate Functions
Port Pin Alternate Function
PA7 AD7 (External memory interface address and data bit 7)
PCINT7 (Pin Change INTerrupt 7)
PA6 AD6 (External memory interface address and data bit 6)
PCINT6 (Pin Change INTerrupt 6)
PA5 AD5 (External memory interface address and data bit 5)
PCINT5 (Pin Change INTerrupt 5)
PA4 AD4 (External memory interface address and data bit 4)
PCINT4 (Pin Change INTerrupt 4)
PA3 AD3 (External memory interface address and data bit 3)
PCINT3 (Pin Change INTerrupt 3)
PA2 AD2 (External memory interface address and data bit 2)
PCINT2 (Pin Change INTerrupt 2)
PA1 AD1 (External memory interface address and data bit 1)
PCINT1 (Pin Change INTerrupt 1)
PA0 AD0 (External memory interface address and data bit 0)
PCINT0 (Pin Change INTerrupt 0)
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Notes: 1. ADA is short for ADdress Active and represents the time when address is output. See “Exter-
nal Memory Interface” on page 26.
2. PCINTn is Pin Change Interrupt Enable bit n.
3. PCINTn is Pin Change Interrupt input n.
Notes: 1. PCINT is Pin Change Interrupt Enable bit n.
2. PCINT is Pin Change Interrupt input n.
Table 30. Overriding Signals for Alternate Functions in PA7..PA4
Signal
Name
PA7/AD7/
PCINT7 PA6/AD6/PCINT6 PA5/AD5/PCINT5 PA4/AD4/PCINT4
PUOE SRE SRE SRE SRE
PUOV ~(WR + ADA(1)) •
PORTA7
~(WR + ADA) •
PORTA6
~(WR + ADA) •
PORTA5
~(WR + ADA) •
PORTA4
DDOE SRE SRE SRE SRE
DDOV WR + ADA WR + ADA WR + ADA WR + ADA
PVOE SRE SRE SRE SRE
PVOV if (ADA) then
A7
else
D7 OUTPUT
• WR
if (ADA) then
A6
else
D6 OUTPUT
• WR
if (ADA) then
A5
else
D5 OUTPUT
• WR
if (ADA) then
A4
else
D4 OUTPUT
• WR
DIEOE(2
)
PCIE0 • PCINT7 PCIE0 • PCINT6 PCIE0 • PCINT5 PCIE0 • PCINT4
DIEOV1111
DI(3) D7 INPUT/
PCINT7
D6 INPUT/
PCINT6
D5 INPUT/
PCINT5
D4 INPUT/
PCINT4
AIO––––
Table 31. Overriding Signals for Alternate Functions in PA3..PA0
Signal
Name
PA3/AD3/
PCINT3
PA2/AD2/
PCINT2
PA1/AD1 /
PCINT1
PA0/AD0 /
PCINT0
PUOE SRE SRE SRE SRE
PUOV ~(WR + ADA) •
PORTA3
~(WR + ADA) •
PORTA2
~(WR + ADA) •
PORTA1
~(WR + ADA) •
PORTA0
DDOE SRE SRE SRE SRE
DDOV WR + ADA WR + ADA WR + ADA WR + ADA
PVOE SRE SRE SRE SRE
PVOV if (ADA) then
A3
else
D3 OUTPUT
• WR
if (ADA) then
A2
else
D2 OUTPUT
• WR
if (ADA) then
A1
else
D1 OUTPUT
• WR
if (ADA) then
A0
else
D0 OUTPUT
• WR
DIEOE(1) PCIE0 • PCINT3 PCIE0 • PCINT2 PCIE0 • PCINT1 PCIE0 • PCINT0
DIEOV 1 1 1 1
DI(2) D3 INPUT
/PCINT3
D2 INPUT
/PCINT2
D1 INPUT
/PCINT1
D0 INPUT
/PCINT0
AIO – – – –
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Alternate Functions Of
Port B
The Port B pins with alternate functions are shown in Table 32.
The alternate pin configuration is as follows:
• SCK – Port B, Bit 7
SCK: Master Clock output, Slave Clock input pin for SPI channel. When the SPI is enabled as a
Slave, this pin is configured as an input regardless of the setting of DDB7. When the SPI is
enabled as a Master, the data direction of this pin is controlled by DDB7. When the pin is forced
by the SPI to be an input, the pull-up can still be controlled by the PORTB7 bit.
• MISO – Port B, Bit 6
MISO: Master Data input, Slave Data output pin for SPI channel. When the SPI is enabled as a
Master, this pin is configured as an input regardless of the setting of DDB6. When the SPI is
enabled as a Slave, the data direction of this pin is controlled by DDB6. When the pin is forced
by the SPI to be an input, the pull-up can still be controlled by the PORTB6 bit.
• MOSI – Port B, Bit 5
MOSI: SPI Master Data output, Slave Data input for SPI channel. When the SPI is enabled as a
Slave, this pin is configured as an input regardless of the setting of DDB5. When the SPI is
enabled as a Master, the data direction of this pin is controlled by DDB5. When the pin is forced
by the SPI to be an input, the pull-up can still be controlled by the PORTB5 bit.
•SS
/OC3B – Port B, Bit 4
SS: Slave Select input. When the SPI is enabled as a slave, this pin is configured as an input
regardless of the setting of DDB4. As a Slave, the SPI is activated when this pin is driven low.
When the SPI is enabled as a Master, the data direction of this pin is controlled by DDB4. When
the pin is forced by the SPI to be an input, the pull-up can still be controlled by the PORTB4 bit.
OC3B, Output Compare Match B output: The PB4 pin can serve as an external output for the
Timer/Counter3 Output Compare B. The pin has to be configured as an output (DDB4 set (one))
to serve this function. The OC3B pin is also the output pin for the PWM mode timer function.
Table 32. Port B Pins Alternate Functions
Port Pin Alternate Functions
PB7 SCK (SPI Bus Serial Clock)
PB6 MISO (SPI Bus Master Input/Slave Output)
PB5 MOSI (SPI Bus Master Output/Slave Input)
PB4 SS (SPI Slave Select Input)
OC3B (Timer/Counter3 Output Compare Match Output)
PB3 AIN1 (Analog Comparator Negative Input)
TXD1 (USART1 Output Pin)
PB2 AIN0 (Analog Comparator Positive Input)
RXD1 (USART1 Input Pin)
PB1 T1 (Timer/Counter1 External Counter Input)
OC2 (Timer/Counter2 Output Compare Match Output)
PB0
T0 (Timer/Counter0 External Counter Input)
OC0 (Timer/Counter0 Output Compare Match Output)
clkI/O (Divided System Clock)
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• AIN1/TXD1 – Port B, Bit 3
AIN1, Analog Comparator Negative input. Configure the port pin as input with the internal pull-up
switched off to avoid the digital port function from interfering with the function of the Analog
Comparator.
TXD1, Transmit Data (Data output pin for USART1). When the USART1 Transmitter is enabled,
this pin is configured as an output regardless of the value of DDB3.
• AIN0/RXD1 – Port B, Bit 2
AIN0, Analog Comparator Positive Input. Configure the port pin as input with the internal pull-up
switched off to avoid the digital port function from interfering with the function of the Analog
Comparator.
RXD1, Receive Data (Data input pin for USART1). When the USART1 Receiver is enabled this
pin is configured as an input regardless of the value of DDB2. When the USART1 forces this pin
to be an input, the pull-up can still be controlled by the PORTB2 bit.
• T1/OC2 – Port B, Bit 1
T1, Timer/Counter1 Counter Source.
OC2, Output Compare Match output: The PB1 pin can serve as an external output for the
Timer/Counter2 Compare Match. The PB1 pin has to be configured as an output (DDB1 set
(one)) to serve this function. The OC2 pin is also the output pin for the PWM mode timer
function.
• T0/OC0 – Port B, Bit 0
T0, Timer/Counter0 counter source.
OC0, Output Compare Match output: The PB0 pin can serve as an external output for the
Timer/Counter0 Compare Match. The PB0 pin has to be configured as an output (DDB0 set
(one)) to serve this function. The OC0 pin is also the output pin for the PWM mode timer
function.
clkI/O, Divided System Clock: The divided system clock can be output on the PB0 pin. The
divided system clock will be output if the CKOUT Fuse is programmed, regardless of the
PORTB0 and DDB0 settings. It will also be output during reset.
Table 33 and Table 34 relate the alternate functions of Port B to the overriding signals shown in
Figure 32 on page 68. SPI MSTR INPUT and SPI SLAVE OUTPUT constitute the MISO signal,
while MOSI is divided into SPI MSTR OUTPUT and SPI SLAVE INPUT.
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Notes: 1. CKOUT is one if the CKOUT Fuse is programmed.
2. clkI/O is the divided system clock.
Table 33. Overriding Signals for Alternate Functions in PB7..PB4
Signal
Name PB7/SCK PB6/MISO PB5/MOSI PB4/SS/OC3B
PUOE SPE • MSTR SPE • MSTR SPE • MSTR SPE • MSTR
PUOV PORTB7 •
PUD
PORTB6 • PUD PORTB5 • PUD PORTB4 •
PUD
DDOE SPE • MSTR SPE • MSTR SPE • MSTR SPE • MSTR
DDOV 0 0 0 0
PVOE SPE • MSTR SPE • MSTR SPE • MSTR OC3B
ENABLE
PVOV SCK OUTPUT SPI SLAVE
OUTPUT
SPI MSTR
OUTPUT
OC3B
DIEOE 0 0 0 0
DIEOV 0 0 0 0
DI SCK INPUT SPI MSTR INPUT SPI SLAVE INPUT SPI SS
AIO – – – –
Table 34. Overriding Signals for Alternate Functions in PB3..PB0
Signal Name PB3/AIN1/TXD1 PB2/AIN0/RXD1 PB1/T1/OC2 PB0/T0/OC0
PUOE TXEN1 RXEN1 0 0
PUOV 0 PORTB2• PUD 0 0
DDOE TXEN1 RXEN1 0 CKOUT(1)
DDOV 1 0 0 1
PVOE TXEN1 0 OC2 ENABLE CKOUT + OC0
ENABLE
PVOV TXD1 0 OC2 if (CKOUT) then
clkI/O(2)
else
OC0
DIEOE 0 0 0 0
DIEOV 0 0 0 0
DI – RXD1 T1 INPUT T0 INPUT
AIO AIN1 INPUT AIN0 INPUT – –
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Alternate Functions of
Port C
The Port C pins with alternate functions are shown in Table 35. If the JTAG interface is enabled,
the pull-up resistors on pins PC7(TDI), PC5(TMS) and PC4(TCK) will be activated even if a reset
occurs.
• A15/TDI/PCINT15 – Port C, Bit 7
A15, External memory interface address bit 15.
TDI, JTAG Test Data In: Serial input data to be shifted into the Instruction Register or Data Reg-
ister (scan chains). When the JTAG interface is enabled, this pin can not be used as an I/O pin.
PCINT15: The pin can also serve as a pin change interrupt.
• A14/TDO/PCINT14 – Port C, Bit 6
A14, External memory interface address bit 14.
TDO, JTAG Test Data Out: Serial output data from Instruction Register or Data Register. When
the JTAG interface is enabled, this pin can not be used as an I/O pin. In TAP states that shift out
data, the TD0 pin drives actively. In other states the pin is pulled high.
PCINT14: The pin can also serve as a pin change interrupt.
Table 35. Port C Pins Alternate Functions
Port Pin Alternate Function
PC7
A15 (External memory interface address bit 15)
TDI (JTAG Test Data Input)
PCINT15 (Pin Change INTerrupt 15)
PC6
A14 (External memory interface address bit 14)
TDO (JTAG Test Data Output)
PCINT14 (Pin Change INTerrupt 14)
PC5
A13 (External memory interface address bit 13)
TMS (JTAG Test Mode Select)
PCINT13 (Pin Change INTerrupt 13)
PC4
A12 (External memory interface address bit 12)
TCK (JTAG Test Clock)
PCINT12 (Pin Change INTerrupt 12)
PC3 A11 (External memory interface address bit 11)
PCINT11 (Pin Change INTerrupt 11)
PC2 A10 (External memory interface address bit 10)
PCINT10 (Pin Change INTerrupt 10)
PC1 A9 (External memory interface address bit 9)
PCINT9 (Pin Change INTerrupt 9)
PC0 A8 (External memory interface address bit 8)
PCINT8 (Pin Change INTerrupt 8)
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• A13/TMS/PCINT13 – Port C, Bit 5
A13, External memory interface address bit 13.
TMS, JTAG Test Mode Select: This pin is used for navigating through the TAP-controller state
machine. When the JTAG interface is enabled, this pin can not be used as an I/O pin.
PCINT13: The pin can also serve as a pin change interrupt.
• A12/TCK/PCINT12 – Port C, Bit 4
A12, External memory interface address bit 12.
TCK, JTAG Test Clock: JTAG operation is synchronous to TCK. When the JTAG interface is
enabled, this pin can not be used as an I/O pin.
PCINT12: The pin can also serve as a pin change interrupt.
• A11/PCINT11 – Port C, Bit 3
A11, External memory interface address bit 11.
PCINT11: The pin can also serve as a pin change interrupt.
• A10/PCINT10 – Port C, Bit 2
A10, External memory interface address bit 10.
PCINT11: The pin can also serve as a pin change interrupt.
• A9/PCINT9 – Port C, Bit 1
A9, External memory interface address bit 9.
PCINT9: The pin can also serve as a pin change interrupt.
• A8/PCINT8 – Port C, Bit 0
A8, External memory interface address bit 8.
PCINT8: The pin can also serve as a pin change interrupt.
Table 36 and Table 37 relate the alternate functions of Port C to the overriding signals shown in
Figure 32 on page 68.
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Notes: 1. PCINTn is Pin Change Interrupt Enable bit n.
2. PCINTn is Pin Change Interrupt input n.
Notes: 1. PCINTn is Pin Change Interrupt Enable bit n.
2. PCINTn is Pin Change Interrupt input n.
Table 36. Overriding Signals for Alternate Functions in PC7..PC4
Signal Name
PC7/A15/TDI
/PCINT15
PC6/A14/TDO
/PCINT14
PC5/A13/TMS
/PCINT13
PC4/A12/TCK
/PCINT12
PUOE (XMM < 1) •
SRE + JTAGEN
(XMM < 2) •
SRE +JTAGEN
(XMM < 3) •
SRE + JTAGEN
(XMM < 4) •
SRE + JTAGEN
PUOV JTAGEN JTAGEN JTAGEN JTAGEN
DDOE SRE • (XMM<1)
+ JTAGEN
SRE • (XMM<2)
+ JTAGEN
SRE • (XMM<3)
+ JTAGEN
SRE • (XMM<4)
+ JTAGEN
DDOV JTAGEN JTAGEN +
JTAGEN •
(SHIFT_IR |
SHIFT_DR)
JTAGEN JTAGEN
PVOE SRE • (XMM<1) SRE • (XMM<2)
+ JTAGEN
SRE • (XMM<3) SRE • (XMM<4)
PVOV A15 if (JTAGEN) then
TDO
else
A14
A13 A12
DIEOE(1) JTAGEN |
PCIE1 •
PCINT15
JTAGEN | PCIE1
• PCINT14
JTAGEN |
PCIE1 •
PCINT13
JTAGEN |
PCIE1 •
PCINT12
DIEOV JTAGEN JTAGEN JTAGEN JTAGEN
DI(2) PCINT15 PCINT14 PCINT13 PCINT12
AIO TDI – TMS TCK
Table 37. Overriding Signals for Alternate Functions in PC3..PC0
Signal Name
PC3/A11/
PCINT11
PC2/A10/
PCINT10 PC1/A9/PCINT9 PC0/A8/PCINT8
PUOE SRE • (XMM<5) SRE • (XMM<6) SRE • (XMM<7) SRE • (XMM<7)
PUOV0000
DDOE SRE • (XMM<5) SRE • (XMM<6) SRE • (XMM<7) SRE • (XMM<7)
DDOV 1 1 1 1
PVOE SRE • (XMM<5) SRE • (XMM<6) SRE • (XMM<7) SRE • (XMM<7)
PVOV A11 A10 A9 A8
DIEOE(1) PCIE1 •
PCINT11
PCIE1 •
PCINT10
PCIE1 • PCINT9 PCIE1 • PCINT8
DIEOV1111
DI(2) PCINT11 PCINT10 PCINT9 PCINT8
AIO––––
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Alternate Functions of
Port D
The Port D pins with alternate functions are shown in Table 38.
The alternate pin configuration is as follows:
•RD
– Port D, Bit 7
RD is the external data memory read control strobe.
•W
R – Port D, Bit 6
WR is the external data memory write control strobe.
• TOSC2/OC1A – Port D, Bit 5
TOSC2, Timer Oscillator pin 2: When the AS2 bit in ASSR is set (one) to enable asynchronous
clocking of Timer/Counter2, pin PD5 is disconnected from the port, and becomes the inverting
output of the Oscillator amplifier. In this mode, a crystal Oscillator is connected to this pin, and
the pin can not be used as an I/O pin.
OC1A, Output Compare Match A output: The PD5 pin can serve as an external output for the
Timer/Counter1 Output Compare A. The pin has to be configured as an output (DDD5 set (one))
to serve this function. The OC1A pin is also the output pin for the PWM mode timer function.
Table 38. Port D Pins Alternate Functions
Port Pin Alternate Function
PD7 RD (Read strobe to external memory)
PD6 WR (Write strobe to external memory)
PD5 TOSC2 (Timer Oscillator Pin 2)
OC1A (Timer/Counter1 Output Compare A Match Output)
PD4
TOSC1 (Timer Oscillator Pin 1)
XCK0 (USART0 External Clock Input/Output)
OC3A (Timer/Counter3 Output Compare A Match Output)
PD3 INT1 (External Interrupt 1 Input)
ICP3 (Timer/Counter3 Input Capture Pin)
PD2 INT0 (External Interrupt 0 Input)
XCK1 (USART1 External Clock Input/Output)
PD1 TXD0 (USART0 Output Pin)
PD0 RXD0 (USART0 Input Pin)
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• TOSC1/XCK0/OC3A – Port D, Bit 4
TOSC1, Timer Oscillator pin 1: When the AS2 bit in ASSR is set (one) to enable asynchronous
clocking of Timer/Counter2, pin PD4 is disconnected from the port, and becomes the input of the
inverting Oscillator Amplifier. In this mode, a crystal Oscillator is connected to this pin, and the
pin can not be used as an I/O pin.
XCK0, USART0 External Clock: The Data Direction Register (DDD4) controls whether the clock
is output (DDD4 set (one)) or input (DDD4 cleared (zero)). The XCK0 pin is active only when
USART0 operates in Synchronous mode.
OC3A, Output Compare Match A output: The PD4 pin can serve as an external output for the
Timer/Counter1 Output Compare A. The pin has to be configured as an output (DDD4 set (one))
to serve this function. The OC4A pin is also the output pin for the PWM mode timer function.
• INT1/ICP3 – Port D, Bit 3
INT1, External Interrupt Source 1: The PD3 pin can serve as an external interrupt source.
ICP3, Input Capture Pin: The PD3 pin can act as an Input Capture pin for Timer/Counter3.
• INT0/XCK1 – Port D, Bit 2
INT0, External Interrupt Source 0: The PD2 pin can serve as an external interrupt source.
XCK1, USART1 External Clock: The Data Direction Register (DDD2) controls whether the clock
is output (DDD2 set (one)) or input (DDD2 cleared (zero)). The XCK1 pin is active only when
USART1 operates in Synchronous mode.
• TXD0 – Port D, Bit 1
TXD0, Transmit Data (Data output pin for USART0). When the USART0 Transmitter is enabled,
this pin is configured as an output regardless of the value of DDD1.
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• RXD0 – Port D, Bit 0
RXD0, Receive Data (Data input pin for USART0). When the USART0 Receiver is enabled this
pin is configured as an input regardless of the value of DDD0. When USART0 forces this pin to
be an input, the pull-up can still be controlled by the PORTD0 bit.
Table 39 and Table 40 relate the alternate functions of Port D to the overriding signals shown in
Figure 32 on page 68.
Table 39. Overriding Signals for Alternate Functions PD7..PD4
Signal Name PD7/RD PD6/WR PD5/TOSC2/OC1A PD4/TOSC1/XCK0/OC3A
PUOE SRE SRE AS2 AS2
PUOV 0 0 0 0
DDOE SRE SRE AS2 AS2
DDOV 1 1 0 0
PVOE SRE SRE OC1A ENABLE XCK0 OUTPUT ENABLE |
OC3A ENABLE
PVOV RD WR OC1A if (XCK0 OUTPUT
ENABLE) then
XCK0 OUTPUT
else
OC3A
DIEOE 0 0 AS2 AS2
DIEOV 0 0 0 0
DI – – – XCK0 INPUT
AIO – – T/C2 OSC OUTPUT T/C2 OSC INPUT
Table 40. Overriding Signals for Alternate Functions in PD3..PD0
Signal Name PD3/INT1 PD2/INT0/XCK1 PD1/TXD0 PD0/RXD0
PUOE 0 0 TXEN0 RXEN0
PUOV 0 0 0 PORTD0 • PUD
DDOE 0 0 TXEN0 RXEN0
DDOV 0 0 1 0
PVOE 0 XCK1 OUTPUT ENABLE TXEN0 0
PVOV 0 XCK1 TXD0 0
DIEOE INT1 ENABLE INT0 ENABLE 0 0
DIEOV 1 1 0 0
DI INT1 INPUT/
ICP1 INPUT
INT0 INPUT/XCK1 INPUT – RXD0
AIO – – – –
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Alternate Functions of
Port E
The Port E pins with alternate functions are shown in Table 41.
The alternate pin configuration is as follows:
• OC1B – Port E, Bit 2
OC1B, Output Compare Match B output: The PE2 pin can serve as an external output for the
Timer/Counter1 Output Compare B. The pin has to be configured as an output (DDE0 set (one))
to serve this function. The OC1B pin is also the output pin for the PWM mode timer function.
Table 42 relate the alternate functions of Port E to the overriding signals shown in Figure 32 on
page 68.
•ALE – Port E, Bit 1
ALE is the external data memory Address Latch Enable signal.
• ICP1/INT2 – Port E, Bit 0
ICP1, Input Capture Pin: The PE0 pin can act as an Input Capture pin for Timer/Counter1.
INT2, External Interrupt Source 2: The PE0 pin can serve as an external interrupt source.
Table 41. Port E Pins Alternate Functions
Port Pin Alternate Function
PE2 OC1B (Timer/Counter1 Output CompareB Match Output)
PE1 ALE (Address Latch Enable to external memory)
PE0 ICP1 (Timer/Counter1 Input Capture Pin)
INT2 (External Interrupt 2 Input)
Table 42. Overriding Signals for Alternate Functions PE2..PE0
Signal Name PE2 PE1 PE0
PUOE 0 SRE 0
PUOV 0 0 0
DDOE 0 SRE 0
DDOV 0 1 0
PVOE OC1B ENABLE SRE 0
PVOV OC1B ALE 0
DIEOE 0 0 INT2 ENABLED
DIEOV 0 0 1
DI 0 0 INT2 INPUT/ ICP1 INPUT
AIO – – –
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Register
Description for I/O-
Ports
Port A Data Register –
PORTA
Port A Data Direction
Register – DDRA
Port A Input Pins
Address – PINA
Port B Data Register –
PORTB
Port B Data Direction
Register – DDRB
Port B Input Pins
Address – PINB
Port C Data Register –
PORTC
Port C Data Direction
Register – DDRC
Bit 76543210
PORTA7 PORTA6 PORTA5 PORTA4 PORTA3 PORTA2 PORTA1 PORTA0 PORTA
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
DDA7 DDA6 DDA5 DDA4 DDA3 DDA2 DDA1 DDA0 DDRA
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
PINA7 PINA6 PINA5 PINA4 PINA3 PINA2 PINA1 PINA0 PINA
Read/WriteRRRRRRRR
Initial Value N/A N/A N/A N/A N/A N/A N/A N/A
Bit 76543210
PORTB7 PORTB6 PORTB5 PORTB4 PORTB3 PORTB2 PORTB1 PORTB0 PORTB
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
DDB7 DDB6 DDB5 DDB4 DDB3 DDB2 DDB1 DDB0 DDRB
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
PINB7 PINB6 PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 PINB
Read/WriteRRRRRRRR
Initial Value N/A N/A N/A N/A N/A N/A N/A N/A
Bit 76543210
PORTC7 PORTC6 PORTC5 PORTC4 PORTC3 PORTC2 PORTC1 PORTC0 PORTC
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
DDC7 DDC6 DDC5 DDC4 DDC3 DDC2 DDC1 DDC0 DDRC
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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Port C Input Pins
Address – PINC
Port D Data Register –
PORTD
Port D Data Direction
Register – DDRD
Port D Input Pins
Address – PIND
Port E Data Register –
PORTE
Port E Data Direction
Register – DDRE
Port E Input Pins
Address – PINE
Bit 76543210
PINC7 PINC6 PINC5 PINC4 PINC3 PINC2 PINC1 PINC0 PINC
Read/WriteRRRRRRRR
Initial Value N/A N/A N/A N/A N/A N/A N/A N/A
Bit 76543210
PORTD7 PORTD6 PORTD5 PORTD4 PORTD3 PORTD2 PORTD1 PORTD0 PORTD
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
DDD7 DDD6 DDD5 DDD4 DDD3 DDD2 DDD1 DDD0 DDRD
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
PIND7 PIND6 PIND5 PIND4 PIND3 PIND2 PIND1 PIND0 PIND
Read/WriteRRRRRRRR
Initial Value N/A N/A N/A N/A N/A N/A N/A N/A
Bit 76543210
–––––PORTE2PORTE1PORTE0PORTE
Read/WriteRRRRRR/WR/WR/W
Initial Value00000000
Bit 76543210
–––––DDE2DDE1DDE0DDRE
Read/WriteRRRRRR/WR/WR/W
Initial Value00000000
Bit 76543210
–––––PINE2PINE1PINE0PINE
Read/WriteRRRRRRRR
Initial Value00000N/AN/AN/A
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External
Interrupts
The External Interrupts are triggered by the INT0, INT1, INT2 pin, or any of the PCINT15..0 pins.
Observe that, if enabled, the interrupts will trigger even if the INT2..0 or PCINT15..0 pins are
configured as outputs. This feature provides a way of generating a software interrupt. The Exter-
nal Interrupts can be triggered by a falling or rising edge or a low level (INT2 is only an edge
triggered interrupt). This is set up as indicated in the specification for the MCU Control Register
– MCUCR and Extended MCU Control Register – EMCUCR. When the external interrupt is
enabled and is configured as level triggered (only INT0/INT1), the interrupt will trigger as long as
the pin is held low. The pin change interrupt PCI1 will trigger if any enabled PCINT15..8 pin tog-
gles. Pin change interrupts PCI0 will trigger if any enabled PCINT7..0 pin toggles. The PCMSK1
and PCMSK0 Registers control which pins contribute to the pin change interrupts. Note that rec-
ognition of falling or rising edge interrupts on INT0 and INT1 requires the presence of an I/O
clock, described in “Clock Systems and their Distribution” on page 35. Low level interrupts on
INT0/INT1, the edge interrupt on INT2, and Pin change interrupts on PCINT15..0 are detected
asynchronously. This implies that these interrupts can be used for waking the part also from
sleep modes other than Idle mode. The I/O clock is halted in all sleep modes except Idle mode.
Note that if a level triggered interrupt is used for wake-up from Power-down mode, the changed
level must be held for some time to wake up the MCU. This makes the MCU less sensitive to
noise. The changed level is sampled twice by the Watchdog Oscillator clock. The period of the
Watchdog Oscillator is 1 µs (nominal) at 5.0V and 25°C. The frequency of the Watchdog Oscilla-
tor is voltage dependent as shown in “Electrical Characteristics” on page 264. The MCU will
wake up if the input has the required level during this sampling or if it is held until the end of the
start-up time. The start-up time is defined by the SUT Fuses as described in “System Clock and
Clock Options” on page 35. If the level is sampled twice by the Watchdog Oscillator clock but
disappears before the end of the start-up time, the MCU will still wake up, but no interrupt will be
generated. The required level must be held long enough for the MCU to complete the wake up to
trigger the level interrupt.
MCU Control Register
– MCUCR
The MCU Control Register contains control bits for interrupt sense control and general MCU
functions.
• Bit 3, 2 – ISC11, ISC10: Interrupt Sense Control 1 Bit 1 and Bit 0
The External Interrupt 1 is activated by the external pin INT1 if the SREG I-bit and the corre-
sponding interrupt mask in the GICR are set. The level and edges on the external INT1 pin that
activate the interrupt are defined in Table 43. The value on the INT1 pin is sampled before
detecting edges. If edge or toggle interrupt is selected, pulses that last longer than one clock
period will generate an interrupt. Shorter pulses are not guaranteed to generate an interrupt. If
low level interrupt is selected, the low level must be held until the completion of the currently
executing instruction to generate an interrupt.
Bit 76543210
SRE SRW10 SE SM1 ISC11 ISC10 ISC01 ISC00 MCUCR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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• Bit 1, 0 – ISC01, ISC00: Interrupt Sense Control 0 Bit 1 and Bit 0
The External Interrupt 0 is activated by the external pin INT0 if the SREG I-flag and the corre-
sponding interrupt mask are set. The level and edges on the external INT0 pin that activate the
interrupt are defined in Table 44. The value on the INT0 pin is sampled before detecting edges.
If edge or toggle interrupt is selected, pulses that last longer than one clock period will generate
an interrupt. Shorter pulses are not guaranteed to generate an interrupt. If low level interrupt is
selected, the low level must be held until the completion of the currently executing instruction to
generate an interrupt.
Extended MCU
Control Register –
EMCUCR
• Bit 0 – ISC2: Interrupt Sense Control 2
The asynchronous External Interrupt 2 is activated by the external pin INT2 if the SREG I-bit and
the corresponding interrupt mask in GICR are set. If ISC2 is cleared (zero), a falling edge on
INT2 activates the interrupt. If ISC2 is set (one), a rising edge on INT2 activates the interrupt.
Edges on INT2 are registered asynchronously. Pulses on INT2 wider than the minimum pulse
width given in Table 45 will generate an interrupt. Shorter pulses are not guaranteed to generate
an interrupt. When changing the ISC2 bit, an interrupt can occur. Therefore, it is recommended
to first disable INT2 by clearing its Interrupt Enable bit in the GICR Register. Then, the ISC2 bit
can be changed. Finally, the INT2 Interrupt Flag should be cleared by writing a logical one to its
Interrupt Flag bit (INTF2) in the GIFR Register before the interrupt is re-enabled.
Table 43. Interrupt 1 Sense Control
ISC11 ISC10 Description
0 0 The low level of INT1 generates an interrupt request.
0 1 Any logical change on INT1 generates an interrupt request.
1 0 The falling edge of INT1 generates an interrupt request.
1 1 The rising edge of INT1 generates an interrupt request.
Table 44. Interrupt 0 Sense Control
ISC01 ISC00 Description
0 0 The low level of INT0 generates an interrupt request.
0 1 Any logical change on INT0 generates an interrupt request.
1 0 The falling edge of INT0 generates an interrupt request.
1 1 The rising edge of INT0 generates an interrupt request.
Bit 76543210
SM0 SRL2 SRL1 SRL0 SRW01 SRW00 SRW11 ISC2 EMCUCR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Table 45. Asynchronous External Interrupt Characteristics
Symbol Parameter Condition Min. Typ. Max. Units
tINT
Minimum pulse width for
asynchronous external interrupt 50 ns
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General Interrupt
Control Register –
GICR
• Bit 7 – INT1: External Interrupt Request 1 Enable
When the INT1 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), the exter-
nal pin interrupt is enabled. The Interrupt Sense Control1 bits 1/0 (ISC11 and ISC10) in the MCU
general Control Register (MCUCR) define whether the external interrupt is activated on rising
and/or falling edge of the INT1 pin or level sensed. Activity on the pin will cause an interrupt
request even if INT1 is configured as an output. The corresponding interrupt of External Interrupt
Request 1 is executed from the INT1 Interrupt Vector.
• Bit 6 – INT0: External Interrupt Request 0 Enable
When the INT0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), the exter-
nal pin interrupt is enabled. The Interrupt Sense Control0 bits 1/0 (ISC01 and ISC00) in the MCU
general Control Register (MCUCR) define whether the external interrupt is activated on rising
and/or falling edge of the INT0 pin or level sensed. Activity on the pin will cause an interrupt
request even if INT0 is configured as an output. The corresponding interrupt of External Interrupt
Request 0 is executed from the INT0 Interrupt Vector.
• Bit 5 – INT2: External Interrupt Request 2 Enable
When the INT2 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), the exter-
nal pin interrupt is enabled. The Interrupt Sense Control2 bit (ISC2) in the Extended MCU
Control Register (EMCUCR) defines whether the external interrupt is activated on rising or fall-
ing edge of the INT2 pin. Activity on the pin will cause an interrupt request even if INT2 is
configured as an output. The corresponding interrupt of External Interrupt Request 2 is executed
from the INT2 Interrupt Vector.
• Bit 4 – PCIE1: Pin Change Interrupt Enable 1
When the PCIE1 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin
change interrupt 1 is enabled. Any change on any enabled PCINT15..8 pin will cause an inter-
rupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI1
Interrupt Vector. PCINT15..8 pins are enabled individually by the PCMSK1 Register.
• Bit 3 – PCIE0: Pin Change Interrupt Enable 0
When the PCIE0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin
change interrupt 0 is enabled. Any change on any enabled PCINT7..0 pin will cause an interrupt.
The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI0 Interrupt
Vector. PCINT7..0 pins are enabled individually by the PCMSK0 Register.
Bit 76543210
INT1 INT0 INT2 PCIE1 PCIE0 –IVSEL IVCE GICR
Read/Write R/W R/W R/W R/W R/W R R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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General Interrupt Flag
Register – GIFR
• Bit 7 – INTF1: External Interrupt Flag 1
When an edge or logic change on the INT1 pin triggers an interrupt request, INTF1 becomes set
(one). If the I-bit in SREG and the INT1 bit in GICR are set (one), the MCU will jump to the corre-
sponding Interrupt Vector. The flag is cleared when the interrupt routine is executed.
Alternatively, the flag can be cleared by writing a logical one to it. This flag is always cleared
when INT1 is configured as a level interrupt.
• Bit 6 – INTF0: External Interrupt Flag 0
When an edge or logic change on the INT0 pin triggers an interrupt request, INTF0 becomes set
(one). If the I-bit in SREG and the INT0 bit in GICR are set (one), the MCU will jump to the corre-
sponding Interrupt Vector. The flag is cleared when the interrupt routine is executed.
Alternatively, the flag can be cleared by writing a logical one to it. This flag is always cleared
when INT0 is configured as a level interrupt.
• Bit 5 – INTF2: External Interrupt Flag 2
When an event on the INT2 pin triggers an interrupt request, INTF2 becomes set (one). If the I-
bit in SREG and the INT2 bit in GICR are set (one), the MCU will jump to the corresponding
Interrupt Vector. The flag is cleared when the interrupt routine is executed. Alternatively, the flag
can be cleared by writing a logical one to it. Note that when entering some sleep modes with the
INT2 interrupt disabled, the input buffer on this pin will be disabled. This may cause a logic
change in internal signals which will set the INTF2 flag. See “Digital Input Enable and Sleep
Modes” on page 67 for more information.
• Bit 4 – PCIF1: Pin Change Interrupt Flag 1
When a logic change on any PCINT15..8 pin triggers an interrupt request, PCIF1 becomes set
(one). If the I-bit in SREG and the PCIE1 bit in GICR are set (one), the MCU will jump to the cor-
responding Interrupt Vector. The flag is cleared when the interrupt routine is executed.
Alternatively, the flag can be cleared by writing a logical one to it.
• Bit 3 – PCIF0: Pin Change Interrupt Flag 0
When a logic change on any PCINT7..0 pin triggers an interrupt request, PCIF0 becomes set
(one). If the I-bit in SREG and the PCIE0 bit in GICR are set (one), the MCU will jump to the cor-
responding Interrupt Vector. The flag is cleared when the interrupt routine is executed.
Alternatively, the flag can be cleared by writing a logical one to it.
Bit 76543210
INTF1 INTF0 INTF2 PCIF1 PCIF0 – – –GIFR
Read/Write R/W R/W R/W R/W R/W R R R
Initial Value 0 0 0 0 0 0 0 0
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Pin Change Mask
Register 1 – PCMSK1
• Bit 7..0 – PCINT15..8: Pin Change Enable Mask 15..8
Each PCINT15..8 bit selects whether pin change interrupt is enabled on the corresponding I/O
pin. If PCINT15..8 is set and the PCIE1 bit in GICR is set, pin change interrupt is enabled on the
corresponding I/O pin. If PCINT15..8 is cleared, pin change interrupt on the corresponding I/O
pin is disabled.
Pin Change Mask
Register 0 – PCMSK0
• Bit 7..0 – PCINT7..0: Pin Change Enable Mask 7..0
Each PCINT7..0 bit selects whether pin change interrupt is enabled on the corresponding I/O
pin. If PCINT7..0 is set and the PCIE0 bit in GICR is set, pin change interrupt is enabled on the
corresponding I/O pin. If PCINT7..0 is cleared, pin change interrupt on the corresponding I/O pin
is disabled.
The mapping between I/O pins and PCINT bits can be found in Figure 1 on page 2. Note that the
Pin Change Mask Register are located in Extended I/O. Thus, the pin change interrupts are not
supported in ATmega161 compatibility mode.
Bit 76543210
PCINT15 PCINT14 PCINT13 PCINT12 PCINT11 PCINT10 PCINT9 PCINT9 PCMSK1
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
PCINT7 PCINT6 PCINT5 PCINT4 PCINT3 PCINT2 PCINT1 PCINT0 PCMSK0
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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8-bit
Timer/Counter0
with PWM
Timer/Counter0 is a general purpose, single channel, 8-bit Timer/Counter module. The main
features are:
•Single Channel Counter
•Clear Timer on Compare Match (Auto Reload)
•Glitch-free, Phase Correct Pulse Width Modulator (PWM)
•Frequency Generator
•External Event Counter
•10-bit Clock Prescaler
•Overflow and Compare Match Interrupt Sources (TOV0 and OCF0)
Overview A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 33. For the actual place-
ment of I/O pins, refer to “Pinout ATmega162” on page 2. CPU accessible I/O Registers,
including I/O bits and I/O pins, are shown in bold. The device-specific I/O Register and bit loca-
tions are listed in the “8-bit Timer/Counter Register Description” on page 100.
Figure 33. 8-bit Timer/Counter Block Diagram
Registers The Timer/Counter (TCNT0) and Output Compare Register (OCR0) are 8-bit registers. Interrupt
request (abbreviated to Int.Req. in the figure) signals are all visible in the Timer Interrupt Flag
Register (TIFR). All interrupts are individually masked with the Timer Interrupt Mask Register
(TIMSK). TIFR and TIMSK are not shown in the figure since these registers are shared by other
timer units.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on
the T0 pin. The Clock Select logic block controls which clock source and edge the Timer/Counter
uses to increment (or decrement) its value. The Timer/Counter is inactive when no clock source
is selected. The output from the clock select logic is referred to as the timer clock (clkT0).
Timer/Counter
DATA BU S
=
TCNTn
Waveform
Generation OCn
= 0
Control Logic
=
0xFF
BOTTOM
count
clear
direction
TOVn
(Int.Req.)
OCRn
TCCRn
Clock Select
Tn
Edge
Detector
( From Prescaler )
clkTn
TOP
OCn
(Int.Req.)
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The double buffered Output Compare Register (OCR0) is compared with the Timer/Counter
value at all times. The result of the compare can be used by the Waveform Generator to gener-
ate a PWM or variable frequency output on the Output Compare pin (OC0). See “Output
Compare Unit” on page 91. for details. The Compare Match event will also set the Compare Flag
(OCF0) which can be used to generate an output compare interrupt request.
Definitions Many register and bit references in this section are written in general form. A lower case “n”
replaces the Timer/Counter number, in this case 0. However, when using the register or bit
defines in a program, the precise form must be used i.e., TCNT0 for accessing Timer/Counter0
counter value and so on.
The definitions in Table 46 are also used extensively throughout the document.
Timer/Counter
Clock Sources
The Timer/Counter can be clocked by an internal or an external clock source. The clock source
is selected by the Clock Select logic which is controlled by the Clock Select (CS02:0) bits
located in the Timer/Counter Control Register (TCCR0). For details on clock sources and pres-
caler, see “Timer/Counter0, Timer/Counter1, and Timer/Counter3 Prescalers” on page 104.
Table 46. Definitions
BOTTOM The counter reaches the BOTTOM when it becomes 0x00.
MAX The counter reaches its MAXimum when it becomes 0xFF (decimal 255).
TOP The counter reaches the TOP when it becomes equal to the highest
value in the count sequence. The TOP value can be assigned to be the
fixed value 0xFF (MAX) or the value stored in the OCR0 Register. The
assignment is dependent on the mode of operation.
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Counter Unit The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure
34 shows a block diagram of the counter and its surroundings.
Figure 34. Counter Unit Block Diagram
Signal description (internal signals):
count Increment or decrement TCNT0 by 1.
direction Select between increment and decrement.
clear Clear TCNT0 (set all bits to zero).
clkTnTimer/Counter clock, referred to as clkT0 in the following.
top Signalize that TCNT0 has reached maximum value.
bottom Signalize that TCNT0 has reached minimum value (zero).
Depending of the mode of operation used, the counter is cleared, incremented, or decremented
at each timer clock (clkT0). clkT0 can be generated from an external or internal clock source,
selected by the clock select bits (CS02:0). When no clock source is selected (CS02:0 = 0) the
timer is stopped. However, the TCNT0 value can be accessed by the CPU, regardless of
whether clkT0 is present or not. A CPU write overrides (has priority over) all counter clear or
count operations.
The counting sequence is determined by the setting of the WGM01 and WGM00 bits located in
the Timer/Counter Control Register (TCCR0). There are close connections between how the
counter behaves (counts) and how waveforms are generated on the output Compare Output
OC0. For more details about advanced counting sequences and waveform generation, see
“Modes of Operation” on page 94.
The Timer/Counter Overflow (TOV0) Flag is set according to the mode of operation selected by
the WGM01:0 bits. TOV0 can be used for generating a CPU interrupt.
Output Compare
Unit
The 8-bit comparator continuously compares TCNT0 with the Output Compare Register
(OCR0). Whenever TCNT0 equals OCR0, the comparator signals a match. A match will set the
Output Compare Flag (OCF0) at the next timer clock cycle. If enabled (OCIE0 = 1 and Global
Interrupt Flag in SREG is set), the Output Compare Flag generates an output compare interrupt.
The OCF0 Flag is automatically cleared when the interrupt is executed. Alternatively, the OCF0
Flag can be cleared by software by writing a logical one to its I/O bit location. The waveform gen-
erator uses the match signal to generate an output according to operating mode set by the
WGM01:0 bits and Compare Output mode (COM01:0) bits. The max and bottom signals are
used by the waveform generator for handling the special cases of the extreme values in some
modes of operation (See “Modes of Operation” on page 94.).
Figure 35 shows a block diagram of the output compare unit.
DATA BU S
TCNTn Control Logic
count
TOVn
(Int.Req.)
Clock Select
top
Tn
Edge
Detector
( From Prescaler )
clkTn
bottom
direction
clear
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Figure 35. Output Compare Unit, Block Diagram
The OCR0 Register is double buffered when using any of the Pulse Width Modulation (PWM)
modes. For the Normal and Clear Timer on Compare (CTC) modes of operation, the double
buffering is disabled. The double buffering synchronizes the update of the OCR0 Compare Reg-
ister to either top or bottom of the counting sequence. The synchronization prevents the
occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.
The OCR0 Register access may seem complex, but this is not case. When the double buffering
is enabled, the CPU has access to the OCR0 Buffer Register, and if double buffering is disabled
the CPU will access the OCR0 directly.
Force Output
Compare
In non-PWM waveform generation modes, the match output of the comparator can be forced by
writing a one to the Force Output Compare (FOC0) bit. Forcing Compare Match will not set the
OCF0 Flag or reload/clear the Timer, but the OC0 pin will be updated as if a real Compare
Match had occurred (the COM01:0 bits settings define whether the OC0 pin is set, cleared or
toggled).
Compare Match
Blocking by TCNT0
Write
All CPU write operations to the TCNT0 Register will block any Compare Match that occur in the
next timer clock cycle, even when the timer is stopped. This feature allows OCR0 to be initialized
to the same value as TCNT0 without triggering an interrupt when the Timer/Counter clock is
enabled.
OCFn (Int.Req.)
= (8-bit Comparator )
OCRn
OCn
DATA B US
TCNTn
WGMn1:0
Waveform Generator
top
FOCn
COMn1:0
bottom
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Using the Output
Compare Unit
Since writing TCNT0 in any mode of operation will block all compare matches for one timer clock
cycle, there are risks involved when changing TCNT0 when using the output compare channel,
independently of whether the Timer/Counter is running or not. If the value written to TCNT0
equals the OCR0 value, the Compare Match will be missed, resulting in incorrect waveform gen-
eration. Similarly, do not write the TCNT0 value equal to BOTTOM when the counter is down-
counting.
The setup of the OC0 should be performed before setting the Data Direction Register for the port
pin to output. The easiest way of setting the OC0 value is to use the Force Output Compare
(FOC0) strobe bits in Normal mode. The OC0 Register keeps its value even when changing
between Waveform Generation modes.
Be aware that the COM01:0 bits are not double buffered together with the compare value.
Changing the COM01:0 bits will take effect immediately.
Compare Match
Output Unit
The Compare Output mode (COM01:0) bits have two functions. The Waveform Generator uses
the COM01:0 bits for defining the Output Compare (OC0) state at the next Compare Match.
Also, the COM01:0 bits control the OC0 pin output source. Figure 36 shows a simplified sche-
matic of the logic affected by the COM01:0 bit setting. The I/O Registers, I/O bits, and I/O pins in
the figure are shown in bold. Only the parts of the general I/O Port Control Registers (DDR and
PORT) that are affected by the COM01:0 bits are shown. When referring to the OC0 state, the
reference is for the internal OC0 Register, not the OC0 pin. If a System Reset occur, the OC0
Register is reset to “0”.
Figure 36. Compare Match Output Unit, Schematics
The general I/O port function is overridden by the Output Compare (OC0) from the waveform
generator if either of the COM01:0 bits are set. However, the OC0 pin direction (input or output)
is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction Regis-
ter bit for the OC0 pin (DDR_OC0) must be set as output before the OC0 value is visible on the
pin. The port override function is independent of the Waveform Generation mode.
PORT
DDR
DQ
DQ
OCn
Pin
OCn
DQ
Waveform
Generator
COMn1
COMn0
0
1
DATA BUS
FOCn
clk
I/O
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The design of the output compare pin logic allows initialization of the OC0 state before the out-
put is enabled. Note that some COM01:0 bit settings are reserved for certain modes of
operation. See “8-bit Timer/Counter Register Description” on page 100.
Compare Output Mode
and Waveform
Generation
The Waveform Generator uses the COM01:0 bits differently in Normal, CTC, and PWM modes.
For all modes, setting the COM01:0 = 0 tells the Waveform Generator that no action on the OC0
Register is to be performed on the next Compare Match. For Compare Output actions in the
non-PWM modes refer to Table 48 on page 101. For fast PWM mode, refer to Table 49 on page
101, and for phase correct PWM refer to Table 50 on page 101.
A change of the COM01:0 bits state will have effect at the first Compare Match after the bits are
written. For non-PWM modes, the action can be forced to have immediate effect by using the
FOC0 strobe bits.
Modes of
Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, is
defined by the combination of the Waveform Generation mode (WGM01:0) and Compare Output
mode (COM01:0) bits. The Compare Output mode bits do not affect the counting sequence,
while the Waveform Generation mode bits do. The COM01:0 bits control whether the PWM out-
put generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes
the COM01:0 bits control whether the output should be set, cleared, or toggled at a Compare
Match (See “Compare Match Output Unit” on page 93.).
For detailed timing information refer to Figure 40, Figure 41, Figure 42 and Figure 43 in
“Timer/Counter Timing Diagrams” on page 98.
Normal Mode The simplest mode of operation is the Normal mode (WGM01:0 = 0). In this mode the counting
direction is always up (incrementing), and no counter clear is performed. The counter simply
overruns when it passes its maximum 8-bit value (TOP = 0xFF) and then restarts from the bot-
tom (0x00). In normal operation the Timer/Counter Overflow Flag (TOV0) will be set in the same
timer clock cycle as the TCNT0 becomes zero. The TOV0 Flag in this case behaves like a ninth
bit, except that it is only set, not cleared. However, combined with the timer overflow interrupt
that automatically clears the TOV0 Flag, the timer resolution can be increased by software.
There are no special cases to consider in the Normal mode, a new counter value can be written
anytime.
The output compare unit can be used to generate interrupts at some given time. Using the out-
put compare to generate waveforms in Normal mode is not recommended, since this will occupy
too much of the CPU time.
Clear Timer on
Compare Match (CTC)
Mode
In Clear Timer on Compare or CTC mode (WGM01:0 = 2), the OCR0 Register is used to manip-
ulate the counter resolution. In CTC mode the counter is cleared to zero when the counter value
(TCNT0) matches the OCR0. The OCR0 defines the top value for the counter, hence also its
resolution. This mode allows greater control of the Compare Match output frequency. It also sim-
plifies the operation of counting external events.
The timing diagram for the CTC mode is shown in Figure 37. The counter value (TCNT0)
increases until a Compare Match occurs between TCNT0 and OCR0, and then counter (TCNT0)
is cleared.
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Figure 37. CTC Mode, Timing Diagram
An interrupt can be generated each time the counter value reaches the TOP value by using the
OCF0 Flag. If the interrupt is enabled, the interrupt handler routine can be used for updating the
TOP value. However, changing TOP to a value close to BOTTOM when the counter is running
with none or a low prescaler value must be done with care since the CTC mode does not have
the double buffering feature. If the new value written to OCR0 is lower than the current value of
TCNT0, the counter will miss the Compare Match. The counter will then have to count to its max-
imum value (0xFF) and wrap around starting at 0x00 before the Compare Match can occur.
For generating a waveform output in CTC mode, the OC0 output can be set to toggle its logical
level on each Compare Match by setting the Compare Output mode bits to toggle bitmode
(COM01:0 = 1). The OC0 value will not be visible on the port pin unless the data direction for the
pin is set to output. The waveform generated will have a maximum frequency of fOC0 = fclk_I/O/2
when OCR0 is set to zero (0x00). The waveform frequency is defined by the following equation:
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
As for the Normal mode of operation, the TOV0 Flag is set in the same timer clock cycle that the
counter counts from MAX to 0x00.
Fast PWM Mode The fast Pulse Width Modulation or fast PWM mode (WGM01:0 = 3) provides a high frequency
PWM waveform generation option. The fast PWM differs from the other PWM option by its sin-
gle-slope operation. The counter counts from BOTTOM to MAX then restarts from BOTTOM. In
non-inverting Compare Output mode, the Output Compare (OC0) is cleared on the Compare
Match between TCNT0 and OCR0, and set at BOTTOM. In inverting Compare Output mode, the
output is set on Compare Match and cleared at BOTTOM. Due to the single-slope operation, the
operating frequency of the fast PWM mode can be twice as high as the phase correct PWM
mode that use dual-slope operation. This high frequency makes the fast PWM mode well suited
for power regulation, rectification, and DAC applications. High frequency allows physically small
sized external components (coils, capacitors), and therefore reduces total system cost.
In fast PWM mode, the counter is incremented until the counter value matches the MAX value.
The counter is then cleared at the following timer clock cycle. The timing diagram for the fast
PWM mode is shown in Figure 38. The TCNT0 value is in the timing diagram shown as a histo-
gram for illustrating the single-slope operation. The diagram includes non-inverted and inverted
PWM outputs. The small horizontal line marks on the TCNT0 slopes represent compare
matches between OCR0 and TCNT0.
TCNTn
OCn
(Toggle)
OCn Interrupt Flag Set
1 4
Period 2 3
(COMn1:0 = 1)
fOCn
fclk_I/O
2N1OCRn+()⋅⋅
-----------------------------------------------=
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ATmega162/V
Figure 38. Fast PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches MAX. If the inter-
rupt is enabled, the interrupt handler routine can be used for updating the compare value.
In fast PWM mode, the compare unit allows generation of PWM waveforms on the OC0 pin. Set-
ting the COM01:0 bits to two will produce a non-inverted PWM and an inverted PWM output can
be generated by setting the COM01:0 to three (See Table 49 on page 101). The actual OC0
value will only be visible on the port pin if the data direction for the port pin is set as output. The
PWM waveform is generated by setting (or clearing) the OC0 Register at the Compare Match
between OCR0 and TCNT0, and clearing (or setting) the OC0 Register at the timer clock cycle
the counter is cleared (changes from MAX to BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
The extreme values for the OCR0 Register represents special cases when generating a PWM
waveform output in the fast PWM mode. If the OCR0 is set equal to BOTTOM, the output will be
a narrow spike for each MAX+1 timer clock cycle. Setting the OCR0 equal to MAX will result in a
constantly high or low output (depending on the polarity of the output set by the COM01:0 bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by set-
ting OC0 to toggle its logical level on each Compare Match (COM01:0 = 1). The waveform
generated will have a maximum frequency of fOC0 = fclk_I/O/2 when OCR0 is set to zero. This fea-
ture is similar to the OC0 toggle in CTC mode, except the double buffer feature of the output
compare unit is enabled in the fast PWM mode.
Phase Correct PWM
Mode
The phase correct PWM mode (WGM01:0 = 1) provides a high resolution phase correct PWM
waveform generation option. The phase correct PWM mode is based on a dual-slope operation.
The counter counts repeatedly from BOTTOM to MAX and then from MAX to BOTTOM. In non-
inverting Compare Output mode, the Output Compare (OC0) is cleared on the Compare Match
between TCNT0 and OCR0 while up-counting, and set on the Compare Match while down-
counting. In inverting Output Compare mode, the operation is inverted. The dual-slope operation
TCNTn
OCRn Update ans
TOVn Interrupt Flag Set
1
Period 2 3
OCn
OCn
(COMn1:0 = 2)
(COMn1:0 = 3)
OCRn Interrupt Flag Set
4 5 6 7
fOCnPWM
fclk_I/O
N256⋅
------------------=
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ATmega162/V
has lower maximum operation frequency than single slope operation. However, due to the sym-
metric feature of the dual-slope PWM modes, these modes are preferred for motor control
applications.
The PWM resolution for the phase correct PWM mode is fixed to eight bits. In phase correct
PWM mode the counter is incremented until the counter value matches MAX. When the counter
reaches MAX, it changes the count direction. The TCNT0 value will be equal to MAX for one
timer clock cycle. The timing diagram for the phase correct PWM mode is shown on Figure 39.
The TCNT0 value is in the timing diagram shown as a histogram for illustrating the dual-slope
operation. The diagram includes non-inverted and inverted PWM outputs. The small horizontal
line marks on the TCNT0 slopes represent compare matches between OCR0 and TCNT0.
Figure 39. Phase Correct PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches BOTTOM. The
Interrupt Flag can be used to generate an interrupt each time the counter reaches the BOTTOM
value.
In phase correct PWM mode, the compare unit allows generation of PWM waveforms on the
OC0 pin. Setting the COM01:0 bits to two will produce a non-inverted PWM. An inverted PWM
output can be generated by setting the COM01:0 to three (See Table 50 on page 101). The
actual OC0 value will only be visible on the port pin if the data direction for the port pin is set as
output. The PWM waveform is generated by clearing (or setting) the OC0 Register at the Com-
pare Match between OCR0 and TCNT0 when the counter increments, and setting (or clearing)
the OC0 Register at Compare Match between OCR0 and TCNT0 when the counter decrements.
The PWM frequency for the output when using phase correct PWM can be calculated by the fol-
lowing equation:
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
TOVn Interrupt Flag Set
OCn Interrupt Flag Set
1 2 3
TCNTn
Period
OCn
OCn
(COMn1:0 = 2)
(COMn1:0 = 3)
OCRn Update
fOCnPCPWM
fclk_I/O
N510⋅
------------------=
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The extreme values for the OCR0 Register represent special cases when generating a PWM
waveform output in the phase correct PWM mode. If the OCR0 is set equal to BOTTOM, the out-
put will be continuously low and if set equal to MAX the output will be continuously high for non-
inverted PWM mode. For inverted PWM the output will have the opposite logic values.
At the very start of period 2 in Figure 39 OCn has a transition from high to low even though there
is no Compare Match. The point of this transition is to guarantee symmetry around BOTTOM.
There are two cases that give a transition without Compare Match.
• OCR0 changes its value from MAX, like in Figure 39. When the OCR0 value is MAX the
OCn pin value is the same as the result of a down-counting Compare Match. To ensure
symmetry around BOTTOM the OCn value at MAX must correspond to the result of an up-
counting Compare Match.
• The timer starts counting from a value higher than the one in OCR0, and for that reason
misses the Compare Match and hence the OCn change that would have happened on the
way up.
Timer/Counter
Timing Diagrams
The Timer/Counter is a synchronous design and the timer clock (clkT0) is therefore shown as a
clock enable signal in the following figures. The figures include information on when Interrupt
Flags are set. Figure 40 contains timing data for basic Timer/Counter operation. The figure
shows the count sequence close to the MAX value in all modes other than phase correct PWM
mode.
Figure 40. Timer/Counter Timing Diagram, no Prescaling
Figure 41 shows the same timing data, but with the prescaler enabled.
Figure 41. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
Figure 42 shows the setting of OCF0 in all modes except CTC mode.
clk
Tn
(clk
I/O
/1)
TOVn
clk
I/O
TCNTn
MAX - 1 MAX BOTTOM BOTTOM + 1
TOVn
TCNTn
MAX - 1 MAX BOTTOM BOTTOM + 1
clk
I/O
clk
Tn
(clk
I/O
/8)
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Figure 42. Timer/Counter Timing Diagram, Setting of OCF0, with Prescaler (fclk_I/O/8)
Figure 43 shows the setting of OCF0 and the clearing of TCNT0 in CTC mode.
Figure 43. Timer/Counter Timing Diagram, Clear Timer on Compare Match Mode, with Pres-
caler (fclk_I/O/8)
OCFn
OCRn
TCNTn
OCRn Value
OCRn - 1 OCRn OCRn + 1 OCRn + 2
clkI/O
clkTn
(clk
I/O
/8)
OCFn
OCRn
TCNTn
(CTC)
TOP
TOP - 1 TOP BOTTOM BOTTOM + 1
clkI/O
clkTn
(clk
I/O
/8)
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ATmega162/V
8-bit
Timer/Counter
Register
Description
Timer/Counter Control
Register – TCCR0
• Bit 7 – FOC0: Force Output Compare
The FOC0 bit is only active when the WGM00 bit specifies a non-PWM mode. However, for
ensuring compatibility with future devices, this bit must be set to zero when TCCR0 is written
when operating in PWM mode. When writing a logical one to the FOC0 bit, an immediate Com-
pare Match is forced on the Waveform Generation unit. The OC0 output is changed according to
its COM01:0 bits setting. Note that the FOC0 bit is implemented as a strobe. Therefore it is the
value present in the COM01:0 bits that determines the effect of the forced compare.
A FOC0 strobe will not generate any interrupt, nor will it clear the timer in CTC mode using
OCR0 as TOP.
The FOC0 bit is always read as zero.
• Bit 6, 3 – WGM01:0: Waveform Generation Mode
These bits control the counting sequence of the counter, the source for the maximum (TOP)
counter value, and what type of waveform generation to be used. Modes of operation supported
by the Timer/Counter unit are: Normal mode, Clear Timer on Compare match (CTC) mode, and
two types of Pulse Width Modulation (PWM) modes. See Table 47 and “Modes of Operation” on
page 94.
Note: 1. The CTC0 and PWM0 bit definition names are now obsolete. Use the WGM01:0 definitions.
However, the functionality and location of these bits are compatible with previous versions of
the timer.
• Bit 5:4 – COM01:0: Compare Match Output Mode
These bits control the output compare pin (OC0) behavior. If one or both of the COM01:0 bits
are set, the OC0 output overrides the normal port functionality of the I/O pin it is connected to.
However, note that the Data Direction Register (DDR) bit corresponding to the OC0 pin must be
set in order to enable the output driver.
Bit 76543210
FOC0 WGM00 COM01 COM00 WGM01 CS02 CS01 CS00 TCCR0
Read/Write W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Table 47. Waveform Generation Mode Bit Description(1)
Mode
WGM01
(CTC0)
WGM00
(PWM0)
Timer/Counter Mode
of Operation TOP
Update of
OCR0 at
TOV0 Flag
Set on
0 0 0 Normal 0xFF Immediate MAX
1 0 1 PWM, Phase Correct 0xFF TOP BOTTOM
2 1 0 CTC OCR0 Immediate MAX
3 1 1 Fast PWM 0xFF TOP MAX
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When OC0 is connected to the pin, the function of the COM01:0 bits depends on the WGM01:0
bit setting. Table 48 shows the COM01:0 bit functionality when the WGM01:0 bits are set to a
Normal or CTC mode (non-PWM).
Table 49 shows the COM01:0 bit functionality when the WGM01:0 bits are set to fast PWM
mode.
Note: 1. A special case occurs when OCR0 equals TOP and COM01 is set. In this case, the Compare
Match is ignored, but the set or clear is done at TOP. See “Fast PWM Mode” on page 95 for
more details.
Table 50 shows the COM01:0 bit functionality when the WGM01:0 bits are set to phase correct
PWM mode.
Note: 1. A special case occurs when OCR0 equals TOP and COM01 is set. In this case, the Compare
Match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” on page
96 for more details.
Table 48. Compare Output Mode, non-PWM Mode
COM01 COM00 Description
0 0 Normal port operation, OC0 disconnected.
0 1 Toggle OC0 on Compare Match.
1 0 Clear OC0 on Compare Match.
1 1 Set OC0 on Compare Match.
Table 49. Compare Output Mode, fast PWM Mode(1)
COM01 COM00 Description
0 0 Normal port operation, OC0 disconnected.
01Reserved
1 0 Clear OC0 on Compare Match, set OC0 at TOP.
1 1 Set OC0 on Compare Match, clear OC0 at TOP.
Table 50. Compare Output Mode, Phase Correct PWM Mode(1)
COM01 COM00 Description
0 0 Normal port operation, OC0 disconnected.
01Reserved
1 0 Clear OC0 on Compare Match when up-counting. Set OC0 on
Compare Match when down-counting.
1 1 Set OC0 on Compare Match when up-counting. Clear OC0 on
Compare Match when down-counting.
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• Bit 2:0 – CS02:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter.
If external pin modes are used for the Timer/Counter0, transitions on the T0 pin will clock the
counter even if the pin is configured as an output. This feature allows software control of the
counting.
Timer/Counter
Register – TCNT0
The Timer/Counter Register gives direct access, both for read and write operations, to the
Timer/Counter unit 8-bit counter. Writing to the TCNT0 Register blocks (removes) the Compare
Match on the following timer clock. Modifying the counter (TCNT0) while the counter is running,
introduces a risk of missing a Compare Match between TCNT0 and the OCR0 Register.
Output Compare
Register – OCR0
The Output Compare Register contains an 8-bit value that is continuously compared with the
counter value (TCNT0). A match can be used to generate an output compare interrupt, or to
generate a waveform output on the OC0 pin.
Timer/Counter
Interrupt Mask
Register – TIMSK
• Bit 1 – TOIE0: Timer/Counter0 Overflow Interrupt Enable
When the TOIE0 bit is written to one, and the I-bit in the Status Register is set (one), the
Timer/Counter0 Overflow interrupt is enabled. The corresponding interrupt is executed if an
overflow in Timer/Counter0 occurs, i.e., when the TOV0 bit is set in the Timer/Counter Interrupt
Flag Register – TIFR.
Table 51. Clock Select Bit Description
CS02 CS01 CS00 Description
0 0 0 No clock source (Timer/Counter stopped).
001clkI/O/(No prescaling)
010
clkI/O/8 (From prescaler)
011
clkI/O/64 (From prescaler)
100
clkI/O/256 (From prescaler)
101
clkI/O/1024 (From prescaler)
1 1 0 External clock source on T0 pin. Clock on falling edge.
1 1 1 External clock source on T0 pin. Clock on rising edge.
Bit 76543210
TCNT0[7:0] TCNT0
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
OCR0[7:0] OCR0
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
TOIE1 OCIE1A OCIE1B OCIE2 TICIE1 TOIE2 TOIE0 OCIE0 TIMSK
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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• Bit 0 – OCIE0: Timer/Counter0 Output Compare Match Interrupt Enable
When the OCIE0 bit is written to one, and the I-bit in the Status Register is set (one), the
Timer/Counter0 Compare Match interrupt is enabled. The corresponding interrupt is executed if
a Compare Match in Timer/Counter0 occurs, i.e., when the OCF0 bit is set in the Timer/Counter
Interrupt Flag Register – TIFR.
Note: In ATmega161 OCIE2 and TOIE2 have switched places in the TIMSK register.
Timer/Counter
Interrupt Flag Register
– TIFR
• Bit 1 – TOV0: Timer/Counter0 Overflow Flag
The bit TOV0 is set (one) when an overflow occurs in Timer/Counter0. TOV0 is cleared by hard-
ware when executing the corresponding interrupt handling vector. Alternatively, TOV0 is cleared
by writing a logic one to the flag. When the SREG I-bit, TOIE0 (Timer/Counter0 Overflow Inter-
rupt Enable), and TOV0 are set (one), the Timer/Counter0 Overflow interrupt is executed. In
phase correct PWM mode, this bit is set when Timer/Counter0 changes counting direction at
0x00.
• Bit 0 – OCF0: Output Compare Flag 0
The OCF0 bit is set (one) when a Compare Match occurs between the Timer/Counter0 and the
data in OCR0 – Output Compare Register0. OCF0 is cleared by hardware when executing the
corresponding interrupt handling vector. Alternatively, OCF0 is cleared by writing a logic one to
the flag. When the I-bit in SREG, OCIE0 (Timer/Counter0 Compare match Interrupt Enable), and
OCF0 are set (one), the Timer/Counter0 Compare Match Interrupt is executed.
Note: In ATmega161 OCF2 and TOV2 have switched places in the TIFR register.
Bit 76543210
TOV1 OCF1A OCF1B OCF2 ICF1 TOV2 TOV0 OCF0 TIFR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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Timer/Counter0,
Timer/Counter1,
and
Timer/Counter3
Prescalers
Timer/Counter3, Timer/Counter1, and Timer/Counter0 share the same prescaler module, but
the Timer/Counters can have different prescaler settings. The description below applies to
Timer/Counter3, Timer/Counter1, and Timer/Counter0.
Internal Clock Source The Timer/Counter can be clocked directly by the system clock (by setting the CSn2:0 = 1). This
provides the fastest operation, with a maximum Timer/Counter clock frequency equal to system
clock frequency (fCLK_I/O). Alternatively, one of four taps from the prescaler can be used as a
clock source. The prescaled clock has a frequency of either fCLK_I/O/8, fCLK_I/O/64, fCLK_I/O/256, or
fCLK_I/O/1024. In addition, Timer/Counter3 has the option of choosing fCLK_I/O/16 and fCLK_I/O/32.
Prescaler Reset The prescaler is free running, i.e., operates independently of the clock select logic of the
Timer/Counter, and it is shared by Timer/Counter3, Timer/Counter1, and Timer/Counter0. Since
the prescaler is not affected by the Timer/Counter’s clock select, the state of the prescaler will
have implications for situations where a prescaled clock is used. One example of prescaling arti-
facts occurs when the Timer is enabled and clocked by the prescaler (6 > CSn2:0 > 1). The
number of system clock cycles from when the Timer is enabled to the first count occurs can be
from 1 to N+1 system clock cycles, where N equals the prescaler divisor (8, 64, 256, or 1024,
additional selections for Timer/Counter3: 32 and 64).
It is possible to use the Prescaler Reset for synchronizing the Timer/Counter to program execu-
tion. However, care must be taken if the other Timer/Counter that shares the same prescaler
also uses prescaling. A Prescaler Reset will affect the prescaler period for all Timer/Counters it
is connected to.
External Clock Source An external clock source applied to the Tn/T0 pin can be used as Timer/Counter clock
(clkT1/clkT0) for Timer/Counter1 and Timer/Counter0. The Tn/T0 pin is sampled once every sys-
tem clock cycle by the pin synchronization logic. The synchronized (sampled) signal is then
passed through the edge detector. Figure 44 shows a functional equivalent block diagram of the
Tn/T0 synchronization and edge detector logic. The registers are clocked at the positive edge of
the internal system clock (clkI/O). The latch is transparent in the high period of the internal system
clock.
The edge detector generates one clkT1/clkT0 pulse for each positive (CSn2:0 = 7) or negative
(CSn2:0 = 6) edge it detects.
Figure 44. Tn/T0 Pin Sampling
The synchronization and edge detector logic introduces a delay of 2.5 to 3.5 system clock cycles
from an edge has been applied to the Tn/T0 pin to the counter is updated.
Enabling and disabling of the clock input must be done when Tn/T0 has been stable for at least
one system clock cycle, otherwise it is a risk that a false Timer/Counter clock pulse is generated.
Tn_sync
(To Clock
Select Logic)
Edge DetectorSynchronization
DQDQ
LE
DQ
Tn
clk
I/O
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ATmega162/V
Each half period of the external clock applied must be longer than one system clock cycle to
ensure correct sampling. The external clock must be guaranteed to have less than half the sys-
tem clock frequency (fExtClk < fclk_I/O/2) given a 50/50% duty cycle. Since the edge detector uses
sampling, the maximum frequency of an external clock it can detect is half the sampling fre-
quency (Nyquist sampling theorem). However, due to variation of the system clock frequency
and duty cycle caused by Oscillator source (crystal, resonator, and capacitors) tolerances, it is
recommended that maximum frequency of an external clock source is less than fclk_I/O/2.5.
An external clock source can not be prescaled.
Figure 45. Prescaler for Timer/Counter0, Timer/Counter1, and Timer/Counter3(1)
Note: 1. The synchronization logic on the input pins (Tn/T0) is shown in Figure 44.
Special Function IO
Register – SFIOR
• Bit 7 – TSM: Timer/Counter Synchronization Mode
Writing the TSM bit to one activates the Timer/Counter Synchronization mode. In this mode, the
value that is written to the PSR2 and PSR310 bits is kept, hence keeping the corresponding
prescaler reset signals asserted. This ensures that the corresponding Timer/Counters are halted
and can be configured to the same value without the risk of one of them advancing during con-
figuration. When the TSM bit is written to zero, the PSR2 and PSR310 bits are cleared by
hardware, and the Timer/Counters start counting simultaneously.
• Bit 0 – PSR310: Prescaler Reset Timer/Counter3, Timer/Counter1, and Timer/Counter0
When this bit is one, the Timer/Counter3, Timer/Counter1, and Timer/Counter0 prescaler will be
reset. This bit is normally cleared immediately by hardware, except if the TSM bit is set. Note
that Timer/Counter3, Timer/Counter1, and Timer/Counter0 share the same prescaler and a
reset of this prescaler will affect all three timers.
PSR321
Clear
clkT1
TIMER/COUNTER1 CLOCK SOURCE
0
CS10
CS11
CS12
T1
clkT0
TIMER/COUNTER1 CLOCK SOURCE
0
CS00
CS01
CS02
T0
clkT3
TIMER/COUNTER3 CLOCK SOURCE
0
CS30
CS31
CS32
10-BIT T/C PRESCALER
CK
CK/8
CK/64
CK/256
CK/1024
CK/16
CK/32
Bit 7 6 5 4 3 2 1 0
TSM XMBK XMM2 XMM1 XMM0 PUD PSR2 PSR310 SFIOR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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ATmega162/V
16-bit
Timer/Counter
(Timer/Counter
1 and
Timer/Counter3
)
The 16-bit Timer/Counter unit allows accurate program execution timing (event management),
wave generation, and signal timing measurement. The main features are:
•True 16-bit Design (i.e., allows 16-bit PWM)
•Two Independent Output Compare Units
•Double Buffered Output Compare Registers
•One Input Capture Unit
•Input Capture Noise Canceler
•Clear Timer on Compare Match (Auto Reload)
•Glitch-free, Phase Correct Pulse Width Modulator (PWM)
•Variable PWM Period
•Frequency Generator
•External Event Counter
•Eight Independent Interrupt Sources (TOV1, OCF1A, OCF1B, ICF1, TOV3, OCF3A, OCF3B, and
ICF3)
Restriction in
ATmega161
Compatibility
Mode
Note that in ATmega161 compatibility mode, only one 16-bits Timer/Counter is available
(Timer/Counter1).
Overview Most register and bit references in this section are written in general form. A lower case “n”
replaces the Timer/Counter number, and a lower case “x” replaces the Output Compare unit
channel. However, when using the register or bit defines in a program, the precise form must be
used i.e., TCNT1 for accessing Timer/Counter1 counter value and so on.
A simplified block diagram of the 16-bit Timer/Counter is shown in Figure 46. For the actual
placement of I/O pins, refer to “Pinout ATmega162” on page 2. CPU accessible I/O Registers,
including I/O bits and I/O pins, are shown in bold. The device-specific I/O Register and bit loca-
tions are listed in the “16-bit Timer/Counter Register Description” on page 128.
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ATmega162/V
Figure 46. 16-bit Timer/Counter Block Diagram(1)
Note: 1. Refer to Figure 1 on page 2, Table 32 on page 72, and Table 38 on page 78 for
Timer/Counter1 pin placement and description.
Registers The Timer/Counter (TCNTn), Output Compare Registers (OCRnA/B), and Input Capture Regis-
ter (ICRn) are all 16-bit registers. Special procedures must be followed when accessing the 16-
bit registers. These procedures are described in the section “Accessing 16-bit Registers” on
page 109. The Timer/Counter Control Registers (TCCRnA/B) are 8-bit registers and have no
CPU access restrictions. Interrupt requests (abbreviated to Int.Req. in the figure) signals are all
visible in the Timer Interrupt Flag Register (TIFR) and Extended Timer Interrupt Flag Register
(ETIFR). All interrupts are individually masked with the Timer Interrupt Mask Register (TIMSK)
and Extended Timer Interrupt Mask Register (ETIMSK). (E)TIFR and (E)TIMSK are not shown in
the figure since these registers are shared by other Timer units.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on
the T1 pin. The Clock Select logic block controls which clock source and edge the Timer/Counter
uses to increment (or decrement) its value. The Timer/Counter is inactive when no clock source
is selected. The output from the Clock Select logic is referred to as the Timer Clock (clkTn).
The double buffered Output Compare Registers (OCRnA/B) are compared with the Timer/Coun-
ter value at all time. The result of the compare can be used by the waveform generator to
generate a PWM or variable frequency output on the Output Compare pin (OCnA/B). See “Out-
put Compare Units” on page 114. The Compare Match event will also set the Compare Match
Flag (OCFnA/B) which can be used to generate an output compare interrupt request.
Clock Select
Timer/Counter
DATABUS
OCRnA
OCRnB
ICRn
=
=
TCNTn
Waveform
Generation
Waveform
Generation
OCnA
OCnB
Noise
Canceler
ICPn
=
Fixed
TOP
Values
Edge
Detector
Control Logic
=
0
TOP BOTTOM
Count
Clear
Direction
TOVn
(Int.Req.)
OCnA
(Int.Req.)
OCnB
(Int.Req.)
ICFn (Int.Req.)
TCCRnA TCCRnB
( From Analog
Comparator Ouput )
Tn
Edge
Detector
( From Prescaler )
clkTn
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ATmega162/V
The Input Capture Register can capture the Timer/Counter value at a given external (edge trig-
gered) event on either the Input Capture pin (ICPn) or on the Analog Comparator pins (See
“Analog Comparator” on page 195.) The Input Capture unit includes a digital filtering unit (Noise
Canceler) for reducing the chance of capturing noise spikes.
The TOP value, or maximum Timer/Counter value, can in some modes of operation be defined
by either the OCRnA Register, the ICRn Register, or by a set of fixed values. When using
OCRnA as TOP value in a PWM mode, the OCRnA Register can not be used for generating a
PWM output. However, the TOP value will in this case be double buffered allowing the TOP
value to be changed in run time. If a fixed TOP value is required, the ICRn Register can be used
as an alternative, freeing the OCRnA to be used as PWM output.
Definitions The following definitions are used extensively throughout the section:
Compatibility The 16-bit Timer/Counter has been updated and improved from previous versions of the 16-bit
AVR Timer/Counter. This 16-bit Timer/Counter is fully compatible with the earlier version
regarding:
• All 16-bit Timer/Counter related I/O Register address locations, including Timer Interrupt
Registers.
• Bit locations inside all 16-bit Timer/Counter Registers, including Timer Interrupt Registers.
• Interrupt Vectors.
The following control bits have changed name, but have same functionality and register location:
• PWMn0 is changed to WGMn0.
• PWMn1 is changed to WGMn1.
• CTCn is changed to WGMn2.
The following bits are added to the 16-bit Timer/Counter Control Registers:
• FOCnA and FOCnB are added to TCCRnA.
• WGMn3 is added to TCCRnB.
The 16-bit Timer/Counter has improvements that will affect the compatibility in some special
cases.
Table 52. Definitions
BOTTOM The counter reaches the BOTTOM when it becomes 0x0000.
MAX The counter reaches its MAXimum when it becomes 0xFFFF (decimal
65535).
TOP The counter reaches the TOP when it becomes equal to the highest
value in the count sequence. The TOP value can be assigned to be one
of the fixed values: 0x00FF, 0x01FF, or 0x03FF, or to the value stored in
the OCRnA or ICRn Register. The assignment is dependent of the mode
of operation.
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Accessing 16-bit
Registers
The TCNTn, OCRnA/B, and ICRn are 16-bit registers that can be accessed by the AVR CPU via
the 8-bit data bus. The 16-bit register must be byte accessed using two read or write operations.
Each 16-bit timer has a single 8-bit register for temporary storing of the high byte of the 16-bit
access. The same Temporary Register is shared between all 16-bit registers within each 16-bit
timer. Accessing the low byte triggers the 16-bit read or write operation. When the low byte of a
16-bit register is written by the CPU, the high byte stored in the temporary register, and the low
byte written are both copied into the 16-bit register in the same clock cycle. When the low byte of
a 16-bit register is read by the CPU, the high byte of the 16-bit register is copied into the tempo-
rary register in the same clock cycle as the low byte is read.
Not all 16-bit accesses uses the temporary register for the high byte. Reading the OCRnA/B 16-
bit registers does not involve using the temporary register.
To do a 16-bit write, the high byte must be written before the low byte. For a 16-bit read, the low
byte must be read before the high byte.
The following code examples show how to access the 16-bit Timer Registers assuming that no
interrupts updates the temporary register. The same principle can be used directly for accessing
the OCRnA/B and ICRn Registers. Note that when using “C”, the compiler handles the 16-bit
access.
Note: 1. The example code assumes that the part specific header file is included.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
The assembly code example returns the TCNTn value in the r17:r16 register pair.
It is important to notice that accessing 16-bit registers are atomic operations. If an interrupt
occurs between the two instructions accessing the 16-bit register, and the interrupt code
updates the temporary register by accessing the same or any other of the 16-bit Timer Regis-
ters, then the result of the access outside the interrupt will be corrupted. Therefore, when both
the main code and the interrupt code update the temporary register, the main code must disable
the interrupts during the 16-bit access.
Assembly Code Examples(1)
...
; Set TCNTn to 0x01FF
ldi r17,0x01
ldi r16,0xFF
out TCNTnH,r17
out TCNTnL,r16
; Read TCNTn into r17:r16
in r16,TCNTnL
in r17,TCNTnH
...
C Code Examples(1)
unsigned int i;
...
/* Set TCNTn to 0x01FF */
TCNTn = 0x1FF;
/* Read TCNTn into i */
i = TCNTn;
...
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The following code examples show how to do an atomic read of the TCNTn Register contents.
Reading any of the OCRnA/B or ICRn Registers can be done by using the same principle.
Note: 1. The example code assumes that the part specific header file is included.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
The assembly code example returns the TCNTn value in the r17:r16 register pair.
Assembly Code Example(1)
TIM16_ReadTCNTn:
; Save Global Inter?upt Flag
in r18,SREG
; Disable interrupt?
cli
; Read TCNTn into r17:r16
in r16,TCNTnL
in r17,TCNTnH
; Restore Global In?errupt Flag
out SREG,r18
ret
C Code Example(1)
unsigned int TIM16_ReadTCNTn( void )
{
unsigned char sreg;
unsigned int i;
/* Save Global Inte?rupt Flag */
sreg = SREG;
/* Disable interrup?s */
_CLI();
/* Read TCNTn into i */
i = TCNTn;
/* Restore Global I?terrupt Flag */
SREG = sreg;
return i;
}
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The following code examples show how to do an atomic write of the TCNTn Register contents.
Writing any of the OCRnA/B or ICRn Registers can be done by using the same principle.
Note: 1. The example code assumes that the part specific header file is included.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
The assembly code example requires that the r17:r16 register pair contains the value to be writ-
ten to TCNTn.
Reusing the
Temporary High Byte
Register
If writing to more than one 16-bit register where the high byte is the same for all registers written,
then the high byte only needs to be written once. However, note that the same rule of atomic
operation described previously also applies in this case.
Assembly Code Example(1)
TIM16_WriteTCNTn:
; Save Global Inter?upt Flag
in r18,SREG
; Disable interrupt?
cli
; Set TCNTn to r17:r16
out TCNTnH,r17
out TCNTnL,r16
; Restore Global In?errupt Flag
out SREG,r18
ret
C Code Example(1)
void TIM16_WriteTCNTn( unsigned int i )
{
unsigned char sreg;
unsigned int i;
/* Save Global Inte?rupt Flag */
sreg = SREG;
/* Disable interrup?s */
_CLI();
/* Set TCNTn to i */
TCNTn = i;
/* Restore Global I?terrupt Flag */
SREG = sreg;
}
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Timer/Counter
Clock Sources
The Timer/Counter can be clocked by an internal or an external clock source. The clock source
is selected by the clock select logic which is controlled by the Clock Select (CSn2:0) bits located
in the Timer/Counter Control Register B (TCCRnB). For details on clock sources and prescaler,
see “Timer/Counter0, Timer/Counter1, and Timer/Counter3 Prescalers” on page 104.
Counter Unit The main part of the 16-bit Timer/Counter is the programmable 16-bit bi-directional counter unit.
Figure 47 shows a block diagram of the counter and its surroundings.
Figure 47. Counter Unit Block Diagram
Signal description (internal signals):
Count Increment or decrement TCNTn by 1.
Direction Select between increment and decrement.
Clear Clear TCNTn (set all bits to zero).
clkTnTimer/Counter clock.
TOP Signalize that TCNTn has reached maximum value.
BOTTOM Signalize that TCNTn has reached minimum value (zero).
The 16-bit counter is mapped into two 8-bit I/O memory locations: Counter High (TCNTnH) con-
taining the upper eight bits of the counter, and Counter Low (TCNTnL) containing the lower eight
bits. The TCNTnH Register can only be indirectly accessed by the CPU. When the CPU does an
access to the TCNTnH I/O location, the CPU accesses the high byte temporary register (TEMP).
The temporary register is updated with the TCNTnH value when the TCNTnL is read, and
TCNTnH is updated with the temporary register value when TCNTnL is written. This allows the
CPU to read or write the entire 16-bit counter value within one clock cycle via the 8-bit data bus.
It is important to notice that there are special cases of writing to the TCNTn Register when the
counter is counting that will give unpredictable results. The special cases are described in the
sections where they are of importance.
Depending on the mode of operation used, the counter is cleared, incremented, or decremented
at each Timer Clock (clkTn). The clkTn can be generated from an external or internal clock
source, selected by the Clock Select bits (CSn2:0). When no clock source is selected (CSn2:0 =
0) the Timer is stopped. However, the TCNTn value can be accessed by the CPU, independent
of whether clkTn is present or not. A CPU write overrides (has priority over) all counter clear or
count operations.
The counting sequence is determined by the setting of the Waveform Generation mode bits
(WGMn3:0) located in the Timer/Counter Control Registers A and B (TCCRnA and TCCRnB).
There are close connections between how the counter behaves (counts) and how waveforms
are generated on the Output Compare outputs OCnx. For more details about advanced counting
sequences and waveform generation, see “Modes of Operation” on page 118.
TEMP (8-bit)
DATA BUS (8-bit)
TCNTn (16-bit Counter)
TCNTnH (8-bit) TCNTnL (8-bit) Control Logic
Count
Clear
Direction
TOVn
(Int.Req.)
Clock Select
TOP BOTTOM
Tn
Edge
Detector
( From Prescaler )
clk
Tn
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The Timer/Counter Overflow Flag (TOVn) is set according to the mode of operation selected by
the WGMn3:0 bits. TOVn can be used for generating a CPU interrupt.
Input Capture Unit The Timer/Counter incorporates an Input Capture unit that can capture external events and give
them a time-stamp indicating time of occurrence. The external signal indicating an event, or mul-
tiple events, can be applied via the ICPn pin or alternatively, via the Analog Comparator unit.
The time-stamps can then be used to calculate frequency, duty-cycle, and other features of the
signal applied. Alternatively the time-stamps can be used for creating a log of the events.
The Input Capture unit is illustrated by the block diagram shown in Figure 48. The elements of
the block diagram that are not directly a part of the Input Capture unit are gray shaded. The
small “n” in register and bit names indicates the Timer/Counter number.
Figure 48. Input Capture Unit Block Diagram(1)
Note: 1. The Analog Comparator Output (ACO) can only trigger the Timer/Counter1 ICP – not
Timer/Counter3.
When a change of the logic level (an event) occurs on the Input Capture pin (ICPn), alternatively
on the Analog Comparator output (ACO), and this change confirms to the setting of the edge
detector, a capture will be triggered. When a capture is triggered, the 16-bit value of the counter
(TCNTn) is written to the Input Capture Register (ICRn). The Input Capture Flag (ICFn) is set at
the same system clock as the TCNTn value is copied into ICRn Register. If enabled (TICIEn =
1), the Input Capture Flag generates an Input Capture interrupt. The ICFn Flag is automatically
cleared when the interrupt is executed. Alternatively the ICFn Flag can be cleared by software
by writing a logical one to its I/O bit location.
Reading the 16-bit value in the Input Capture Register (ICRn) is done by first reading the low
byte (ICRnL) and then the high byte (ICRnH). When the low byte is read the high byte is copied
into the high byte temporary register (TEMP). When the CPU reads the ICRnH I/O location it will
access the TEMP Register.
The ICRn Register can only be written when using a Waveform Generation mode that utilizes
the ICRn Register for defining the counter’s TOP value. In these cases the Waveform Genera-
ICFn (Int.Req.)
Analog
Comparator
WRITE ICRn (16-bit Register)
ICRnH (8-bit)
Noise
Canceler
ICPn
Edge
Detector
TEMP (8-bit)
DATA BUS (8-bit)
ICRnL (8-bit)
TCNTn (16-bit Counter)
TCNTnH (8-bit) TCNTnL (8-bit)
ACIC* ICNC ICES
ACO*
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tion mode (WGMn3:0) bits must be set before the TOP value can be written to the ICRn
Register. When writing the ICRn Register the high byte must be written to the ICRnH I/O location
before the low byte is written to ICRnL.
For more information on how to access the 16-bit registers refer to “Accessing 16-bit Registers”
on page 109.
Input Capture Trigger
Source
The main trigger source for the Input Capture unit is the Input Capture pin (ICPn).
Timer/Counter1 can alternatively use the Analog Comparator output as trigger source for the
Input Capture unit. The Analog Comparator is selected as trigger source by setting the Analog
Comparator Input Capture (ACIC) bit in the Analog Comparator Control and Status Register
(ACSR). Be aware that changing trigger source can trigger a capture. The Input Capture Flag
must therefore be cleared after the change.
Both the Input Capture pin (ICPn) and the Analog Comparator output (ACO) inputs are sampled
using the same technique as for the Tn pin (Figure 44 on page 104). The edge detector is also
identical. However, when the noise canceler is enabled, additional logic is inserted before the
edge detector, which increases the delay by four system clock cycles. Note that the input of the
noise canceler and edge detector is always enabled unless the Timer/Counter is set in a Wave-
form Generation mode that uses ICRn to define TOP.
An Input Capture can be triggered by software by controlling the port of the ICPn pin.
Noise Canceler The Noise Canceler improves noise immunity by using a simple digital filtering scheme. The
Noise Canceler input is monitored over four samples, and all four must be equal for changing the
output that in turn is used by the edge detector.
The Noise Canceler is enabled by setting the Input Capture Noise Canceler (ICNCn) bit in
Timer/Counter Control Register B (TCCRnB). When enabled the noise canceler introduces addi-
tional four system clock cycles of delay from a change applied to the input, to the update of the
ICRn Register. The noise canceler uses the system clock and is therefore not affected by the
prescaler.
Using the Input
Capture Unit
The main challenge when using the Input Capture unit is to assign enough processor capacity
for handling the incoming events. The time between two events is critical. If the processor has
not read the captured value in the ICRn Register before the next event occurs, the ICRn will be
overwritten with a new value. In this case the result of the capture will be incorrect.
When using the Input Capture interrupt, the ICRn Register should be read as early in the inter-
rupt handler routine as possible. Even though the Input Capture interrupt has relatively high
priority, the maximum interrupt response time is dependent on the maximum number of clock
cycles it takes to handle any of the other interrupt requests.
Using the Input Capture unit in any mode of operation when the TOP value (resolution) is
actively changed during operation, is not recommended.
Measurement of an external signal’s duty cycle requires that the trigger edge is changed after
each capture. Changing the edge sensing must be done as early as possible after the ICRn
Register has been read. After a change of the edge, the Input Capture Flag (ICFn) must be
cleared by software (writing a logical one to the I/O bit location). For measuring frequency only,
the clearing of the ICFn Flag is not required (if an interrupt handler is used).
Output Compare
Units
The 16-bit comparator continuously compares TCNTn with the Output Compare Register
(OCRnx). If TCNT equals OCRnx the comparator signals a match. A match will set the Output
Compare Flag (OCFnx) at the next timer clock cycle. If enabled (OCIEnx = 1), the Output Com-
pare Flag generates an output compare interrupt. The OCFnx Flag is automatically cleared
when the interrupt is executed. Alternatively the OCFnx Flag can be cleared by software by writ-
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ing a logical one to its I/O bit location. The Waveform Generator uses the match signal to
generate an output according to operating mode set by the Waveform Generation mode
(WGMn3:0) bits and Compare Output mode (COMnx1:0) bits. The TOP and BOTTOM signals
are used by the Waveform Generator for handling the special cases of the extreme values in
some modes of operation (See “Modes of Operation” on page 118.)
A special feature of output compare unit A allows it to define the Timer/Counter TOP value (i.e.,
counter resolution). In addition to the counter resolution, the TOP value defines the period time
for waveforms generated by the Waveform Generator.
Figure 49 shows a block diagram of the output compare unit. The small “n” in the register and bit
names indicates the device number (n = n for Timer/Counter n), and the “x” indicates output
compare unit (A/B). The elements of the block diagram that are not directly a part of the output
compare unit are gray shaded.
Figure 49. Output Compare Unit, Block Diagram
The OCRnx Register is double buffered when using any of the twelve Pulse Width Modulation
(PWM) modes. For the normal and Clear Timer on Compare (CTC) modes of operation, the dou-
ble buffering is disabled. The double buffering synchronizes the update of the OCRnx Compare
Register to either TOP or BOTTOM of the counting sequence. The synchronization prevents the
occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.
The OCRnx Register access may seem complex, but this is not case. When the double buffering
is enabled, the CPU has access to the OCRnx Buffer Register, and if double buffering is dis-
abled the CPU will access the OCRnx directly. The content of the OCR1x (Buffer or Compare)
Register is only changed by a write operation (the Timer/Counter does not update this register
automatically as the TCNT1 and ICR1 Register). Therefore OCR1x is not read via the high byte
temporary register (TEMP). However, it is a good practice to read the low byte first as when
accessing other 16-bit registers. Writing the OCRnx Registers must be done via the TEMP Reg-
ister since the compare of all 16 bits is done continuously. The high byte (OCRnxH) has to be
written first. When the high byte I/O location is written by the CPU, the TEMP Register will be
OCFnx (Int.Req.)
= (16-bit Comparator )
OCRnx Buffer (16-bit Register)
OCRnxH Buf. (8-bit)
OCnx
TEMP (8-bit)
DATA BUS (8-bit)
OCRnxL Buf. (8-bit)
TCNTn (16-bit Counter)
TCNTnH (8-bit) TCNTnL (8-bit)
COMnx1:0WGMn3:0
OCRnx (16-bit Register)
OCRnxH (8-bit) OCRnxL (8-bit)
Waveform Generator
TOP
BOTTOM
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updated by the value written. Then when the low byte (OCRnxL) is written to the lower eight bits,
the high byte will be copied into the upper eight bits of either the OCRnx buffer or OCRnx Com-
pare Register in the same system clock cycle.
For more information of how to access the 16-bit registers refer to “Accessing 16-bit Registers”
on page 109.
Force Output
Compare
In non-PWM waveform generation modes, the match output of the comparator can be forced by
writing a one to the Force Output Compare (FOCnx) bit. Forcing Compare Match will not set the
OCFnx Flag or reload/clear the timer, but the OCnx pin will be updated as if a real Compare
Match had occurred (the COMn1:0 bits settings define whether the OCnx pin is set, cleared or
toggled).
Compare Match
Blocking by TCNTn
Write
All CPU writes to the TCNTn Register will block any Compare Match that occurs in the next timer
clock cycle, even when the timer is stopped. This feature allows OCRnx to be initialized to the
same value as TCNTn without triggering an interrupt when the Timer/Counter clock is enabled.
Using the Output
Compare Unit
Since writing TCNTn in any mode of operation will block all compare matches for one timer clock
cycle, there are risks involved when changing TCNTn when using any of the output compare
channels, independent of whether the Timer/Counter is running or not. If the value written to
TCNTn equals the OCRnx value, the Compare Match will be missed, resulting in incorrect wave-
form generation. Do not write the TCNTn equal to TOP in PWM modes with variable TOP
values. The Compare Match for the TOP will be ignored and the counter will continue to
0xFFFF. Similarly, do not write the TCNTn value equal to BOTTOM when the counter is down-
counting.
The setup of the OCnx should be performed before setting the Data Direction Register for the
port pin to output. The easiest way of setting the OCnx value is to use the Force Output Com-
pare (FOCnx) strobe bits in Normal mode. The OCnx Register keeps its value even when
changing between Waveform Generation modes.
Be aware that the COMnx1:0 bits are not double buffered together with the compare value.
Changing the COMnx1:0 bits will take effect immediately.
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Compare Match
Output Unit
The Compare Output mode (COMnx1:0) bits have two functions. The waveform generator uses
the COMnx1:0 bits for defining the output compare (OCnx) state at the next Compare Match.
Secondly the COMnx1:0 bits control the OCnx pin output source. Figure 50 shows a simplified
schematic of the logic affected by the COMnx1:0 bit setting. The I/O Registers, I/O bits, and I/O
pins in the figure are shown in bold. Only the parts of the general I/O Port Control Registers
(DDR and PORT) that are affected by the COMnx1:0 bits are shown. When referring to the
OCnx state, the reference is for the internal OCnx Register, not the OCnx pin. If a System Reset
occur, the OCnx Register is reset to “0”.
Figure 50. Compare Match Output Unit, Schematic
The general I/O port function is overridden by the output compare (OCnx) from the Waveform
Generator if either of the COMnx1:0 bits are set. However, the OCnx pin direction (input or out-
put) is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction
Register bit for the OCnx pin (DDR_OCnx) must be set as output before the OCnx value is visi-
ble on the pin. The port override function is generally independent of the Waveform Generation
mode, but there are some exceptions. Refer to Table 53, Table 54 and Table 55 for details.
The design of the output compare pin logic allows initialization of the OCnx state before the out-
put is enabled. Note that some COMnx1:0 bit settings are reserved for certain modes of
operation. See “16-bit Timer/Counter Register Description” on page 128.
The COMnx1:0 bits have no effect on the Input Capture unit.
PORT
DDR
DQ
DQ
OCnx
Pin
OCnx
DQ
Waveform
Generator
COMnx1
COMnx0
0
1
DATA B US
FOCnx
clkI/O
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Compare Output Mode
and Waveform
Generation
The Waveform Generator uses the COMnx1:0 bits differently in normal, CTC, and PWM modes.
For all modes, setting the COMnx1:0 = 0 tells the Waveform Generator that no action on the
OCnx Register is to be performed on the next Compare Match. For Compare Output actions in
the non-PWM modes refer to Table 53 on page 128. For fast PWM mode refer to Table 54 on
page 129, and for phase correct and phase and frequency correct PWM refer to Table 55 on
page 129.
A change of the COMnx1:0 bits state will have effect at the first Compare Match after the bits are
written. For non-PWM modes, the action can be forced to have immediate effect by using the
FOCnx strobe bits.
Modes of
Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, is
defined by the combination of the Waveform Generation mode (WGMn3:0) and Compare Output
mode (COMnx1:0) bits. The Compare Output mode bits do not affect the counting sequence,
while the Waveform Generation mode bits do. The COMnx1:0 bits control whether the PWM out-
put generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes
the COMnx1:0 bits control whether the output should be set, cleared or toggle at a Compare
Match (See “Compare Match Output Unit” on page 117.)
For detailed timing information refer to “Timer/Counter Timing Diagrams” on page 126.
Normal Mode The simplest mode of operation is the Normal mode (WGMn3:0 = 0). In this mode the counting
direction is always up (incrementing), and no counter clear is performed. The counter simply
overruns when it passes its maximum 16-bit value (MAX = 0xFFFF) and then restarts from the
BOTTOM (0x0000). In normal operation the Timer/Counter Overflow Flag (TOVn) will be set in
the same timer clock cycle as the TCNTn becomes zero. The TOVn Flag in this case behaves
like a 17th bit, except that it is only set, not cleared. However, combined with the timer overflow
interrupt that automatically clears the TOVn Flag, the timer resolution can be increased by soft-
ware. There are no special cases to consider in the normal mode, a new counter value can be
written anytime.
The Input Capture unit is easy to use in Normal mode. However, observe that the maximum
interval between the external events must not exceed the resolution of the counter. If the interval
between events are too long, the timer overflow interrupt or the prescaler must be used to
extend the resolution for the capture unit.
The Output Compare units can be used to generate interrupts at some given time. Using the
Output Compare to generate waveforms in Normal mode is not recommended, since this will
occupy too much of the CPU time.
Clear Timer on
Compare Match (CTC)
Mode
In Clear Timer on Compare or CTC mode (WGMn3:0 = 4 or 12), the OCRnA or ICRn Register
are used to manipulate the counter resolution. In CTC mode the counter is cleared to zero when
the counter value (TCNTn) matches either the OCRnA (WGMn3:0 = 4) or the ICRn (WGMn3:0 =
12). The OCRnA or ICRn define the top value for the counter, hence also its resolution. This
mode allows greater control of the Compare Match output frequency. It also simplifies the oper-
ation of counting external events.
The timing diagram for the CTC mode is shown in Figure 51. The counter value (TCNTn)
increases until a Compare Match occurs with either OCRnA or ICRn, and then counter (TCNTn)
is cleared.
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Figure 51. CTC Mode, Timing Diagram
An interrupt can be generated at each time the counter value reaches the TOP value by either
using the OCFnA or ICFn Flag according to the register used to define the TOP value. If the
interrupt is enabled, the interrupt handler routine can be used for updating the TOP value. How-
ever, changing the TOP to a value close to BOTTOM when the counter is running with none or a
low prescaler value must be done with care since the CTC mode does not have the double buff-
ering feature. If the new value written to OCRnA or ICRn is lower than the current value of
TCNTn, the counter will miss the Compare Match. The counter will then have to count to its max-
imum value (0xFFFF) and wrap around starting at 0x0000 before the Compare Match can occur.
In many cases this feature is not desirable. An alternative will then be to use the fast PWM mode
using OCRnA for defining TOP (WGMn3:0 = 15) since the OCRnA then will be double buffered.
For generating a waveform output in CTC mode, the OCnA output can be set to toggle its logical
level on each Compare Match by setting the Compare Output mode bits to toggle mode
(COMnA1:0 = 1). The OCnA value will not be visible on the port pin unless the data direction for
the pin is set to output (DDR_OCnA = 1). The waveform generated will have a maximum fre-
quency of fOCnA = fclk_I/O/2 when OCRnA is set to zero (0x0000). The waveform frequency is
defined by the following equation:
The N variable represents the prescaler factor (1, 8, 64, 256, or 1024). For Timer/Counter3 also
prescaler factors 16 and 32 are available.
As for the Normal mode of operation, the TOVn Flag is set in the same timer clock cycle that the
counter counts from MAX to 0x0000.
TCNTn
OCnA
(Toggle)
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
1 4
Period
2 3
(COMnA1:0 = 1)
fOCnA
fclk_I/O
2N1OCRnA+()⋅⋅
---------------------------------------------------=
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Fast PWM Mode The fast Pulse Width Modulation or fast PWM mode (WGMn3:0 = 5,6,7,14, or 15) provides a
high frequency PWM waveform generation option. The fast PWM differs from the other PWM
options by its single-slope operation. The counter counts from BOTTOM to TOP then restarts
from BOTTOM. In non-inverting Compare Output mode, the Output Compare (OCnx) is set on
the Compare Match between TCNTn and OCRnx, and cleared at TOP. In inverting Compare
Output mode output is cleared on Compare Match and set at TOP. Due to the single-slope oper-
ation, the operating frequency of the fast PWM mode can be twice as high as the phase correct
and phase and frequency correct PWM modes that use dual-slope operation. This high fre-
quency makes the fast PWM mode well suited for power regulation, rectification, and DAC
applications. High frequency allows physically small sized external components (coils, capaci-
tors), hence reduces total system cost.
The PWM resolution for fast PWM can be fixed to 8-, 9-, or 10-bit, or defined by either ICRn or
OCRnA. The minimum resolution allowed is 2-bit (ICRn or OCRnA set to 0x0003), and the max-
imum resolution is 16-bit (ICRn or OCRnA set to MAX). The PWM resolution in bits can be
calculated by using the following equation:
In fast PWM mode the counter is incremented until the counter value matches either one of the
fixed values 0x00FF, 0x01FF, or 0x03FF (WGMn3:0 = 5, 6, or 7), the value in ICRn (WGMn3:0 =
14), or the value in OCRnA (WGMn3:0 = 15). The counter is then cleared at the following timer
clock cycle. The timing diagram for the fast PWM mode is shown in Figure 52. The figure shows
fast PWM mode when OCRnA or ICRn is used to define TOP. The TCNTn value is in the timing
diagram shown as a histogram for illustrating the single-slope operation. The diagram includes
non-inverted and inverted PWM outputs. The small horizontal line marks on the TCNTn slopes
represent compare matches between OCRnx and TCNTn. The OCnx Interrupt Flag will be set
when a Compare Match occurs.
Figure 52. Fast PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOVn) is set each time the counter reaches TOP. In addition
the OCnA or ICFn Flag is set at the same timer clock cycle as TOVn is set when either OCRnA
or ICRn is used for defining the TOP value. If one of the interrupts are enabled, the interrupt han-
dler routine can be used for updating the TOP and compare values.
When changing the TOP value the program must ensure that the new TOP value is higher or
equal to the value of all of the compare registers. If the TOP value is lower than any of the com-
RFPWM
TOP 1+()log
2()log
-----------------------------------=
TCNTn
OCRnx / TOP Update
and TOVn Interrupt Flag
Set and OCnA Interrupt
Flag Set or ICFn
Interrupt Flag Set
(Interrupt on TOP)
1 7
Period
2 3 4 5 6 8
OCnx
OCnx
(COMnx1:0 = 2)
(COMnx1:0 = 3)
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ATmega162/V
pare registers, a Compare Match will never occur between the TCNTn and the OCRnx. Note
that when using fixed TOP values the unused bits are masked to zero when any of the OCRnx
Registers are written.
The procedure for updating ICRn differs from updating OCRnA when used for defining the TOP
value. The ICRn Register is not double buffered. This means that if ICRn is changed to a low
value when the counter is running with none or a low prescaler value, there is a risk that the new
ICRn value written is lower than the current value of TCNTn. The result will then be that the
counter will miss the Compare Match at the TOP value. The counter will then have to count to
the MAX value (0xFFFF) and wrap around starting at 0x0000 before the Compare Match can
occur. The OCRnA Register however, is double buffered. This feature allows the OCRnA I/O
location to be written anytime. When the OCRnA I/O location is written the value written will be
put into the OCRnA Buffer Register. The OCRnA Compare Register will then be updated with
the value in the Buffer Register at the next timer clock cycle the TCNTn matches TOP. The
update is done at the same timer clock cycle as the TCNTn is cleared and the TOVn Flag is set.
Using the ICRn Register for defining TOP works well when using fixed TOP values. By using
ICRn, the OCRnA Register is free to be used for generating a PWM output on OCnA. However,
if the base PWM frequency is actively changed (by changing the TOP value), using the OCRnA
as TOP is clearly a better choice due to its double buffer feature.
In fast PWM mode, the compare units allow generation of PWM waveforms on the OCnx pins.
Setting the COMnx1:0 bits to two will produce a non-inverted PWM and an inverted PWM output
can be generated by setting the COMnx1:0 to three (See Table on page 129). The actual OCnx
value will only be visible on the port pin if the data direction for the port pin is set as output
(DDR_OCnx). The PWM waveform is generated by setting (or clearing) the OCnx Register at
the Compare Match between OCRnx and TCNTn, and clearing (or setting) the OCnx Register at
the timer clock cycle the counter is cleared (changes from TOP to BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024). For Timer/Counter3 also
prescaler factors 16 and 32 are available.
The extreme values for the OCRnx Register represents special cases when generating a PWM
waveform output in the fast PWM mode. If the OCRnx is set equal to BOTTOM (0x0000) the out-
put will be a narrow spike for each TOP+1 timer clock cycle. Setting the OCRnx equal to TOP
will result in a constant high or low output (depending on the polarity of the output set by the
COMnx1:0 bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by set-
ting OCnA to toggle its logical level on each Compare Match (COMnA1:0 = 1). This applies only
if OCRnA is used to define the TOP value (WGMn3:0 = 15). The waveform generated will have
a maximum frequency of fOCnA = fclk_I/O/2 when OCRnA is set to zero (0x0000). This feature is
similar to the OCnA toggle in CTC mode, except the double buffer feature of the output compare
unit is enabled in the fast PWM mode.
fOCnxPWM
fclk_I/O
N1TOP+()⋅
-----------------------------------=
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Phase Correct PWM
Mode
The phase correct Pulse Width Modulation or phase correct PWM mode (WGMn3:0 = 1, 2, 3,
10, or 11) provides a high resolution phase correct PWM waveform generation option. The
phase correct PWM mode is, like the phase and frequency correct PWM mode, based on a dual-
slope operation. The counter counts repeatedly from BOTTOM (0x0000) to TOP and then from
TOP to BOTTOM. In non-inverting Compare Output mode, the Output Compare (OCnx) is
cleared on the Compare Match between TCNTn and OCRnx while up-counting, and set on the
Compare Match while down-counting. In inverting Output Compare mode, the operation is
inverted. The dual-slope operation has lower maximum operation frequency than single slope
operation. However, due to the symmetric feature of the dual-slope PWM modes, these modes
are preferred for motor control applications.
The PWM resolution for the phase correct PWM mode can be fixed to 8-, 9-, or 10-bit, or defined
by either ICRn or OCRnA. The minimum resolution allowed is 2-bit (ICRn or OCRnA set to
0x0003), and the maximum resolution is 16-bit (ICRn or OCRnA set to MAX). The PWM resolu-
tion in bits can be calculated by using the following equation:
In phase correct PWM mode the counter is incremented until the counter value matches either
one of the fixed values 0x00FF, 0x01FF, or 0x03FF (WGMn3:0 = 1, 2, or 3), the value in ICRn
(WGMn3:0 = 10), or the value in OCRnA (WGMn3:0 = 11). The counter has then reached the
TOP and changes the count direction. The TCNTn value will be equal to TOP for one timer clock
cycle. The timing diagram for the phase correct PWM mode is shown on Figure 53. The figure
shows phase correct PWM mode when OCRnA or ICRn is used to define TOP. The TCNTn
value is in the timing diagram shown as a histogram for illustrating the dual-slope operation. The
diagram includes non-inverted and inverted PWM outputs. The small horizontal line marks on
the TCNTn slopes represent compare matches between OCRnx and TCNTn. The OCnx Inter-
rupt Flag will be set when a Compare Match occurs.
Figure 53. Phase Correct PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOVn) is set each time the counter reaches BOTTOM. When
either OCRnA or ICRn is used for defining the TOP value, the OCnA or ICFn Flag is set accord-
ingly at the same timer clock cycle as the OCRnx Registers are updated with the double buffer
RPCPWM
TOP 1+()log
2()log
-----------------------------------=
OCRnx/TOP Update and
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
1 2 3 4
TOVn Interrupt Flag Set
(Interrupt on Bottom)
TCNTn
Period
OCnx
OCnx
(COMnx1:0 = 2)
(COMnx1:0 = 3)
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value (at TOP). The Interrupt Flags can be used to generate an interrupt each time the counter
reaches the TOP or BOTTOM value.
When changing the TOP value the program must ensure that the new TOP value is higher or
equal to the value of all of the compare registers. If the TOP value is lower than any of the com-
pare registers, a Compare Match will never occur between the TCNTn and the OCRnx. Note
that when using fixed TOP values, the unused bits are masked to zero when any of the OCRnx
Registers are written. As the third period shown in Figure 53 illustrates, changing the TOP
actively while the Timer/Counter is running in the phase correct mode can result in an unsym-
metrical output. The reason for this can be found in the time of update of the OCRnx Register.
Since the OCRnx update occurs at TOP, the PWM period starts and ends at TOP. This implies
that the length of the falling slope is determined by the previous TOP value, while the length of
the rising slope is determined by the new TOP value. When these two values differ the two
slopes of the period will differ in length. The difference in length gives the unsymmetrical result
on the output.
It is recommended to use the phase and frequency correct mode instead of the phase correct
mode when changing the TOP value while the Timer/Counter is running. When using a static
TOP value there are practically no differences between the two modes of operation.
In phase correct PWM mode, the compare units allow generation of PWM waveforms on the
OCnx pins. Setting the COMnx1:0 bits to two will produce a non-inverted PWM and an inverted
PWM output can be generated by setting the COMnx1:0 to three (See Table 55 on page 129).
The actual OCnx value will only be visible on the port pin if the data direction for the port pin is
set as output (DDR_OCnx). The PWM waveform is generated by setting (or clearing) the OCnx
Register at the Compare Match between OCRnx and TCNTn when the counter increments, and
clearing (or setting) the OCnx Register at Compare Match between OCRnx and TCNTn when
the counter decrements. The PWM frequency for the output when using phase correct PWM can
be calculated by the following equation:
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024). For Timer/Counter3 also
prescaler factors 16 and 32 are available.
The extreme values for the OCRnx Register represent special cases when generating a PWM
waveform output in the phase correct PWM mode. If the OCRnx is set equal to BOTTOM the
output will be continuously low and if set equal to TOP the output will be continuously high for
non-inverted PWM mode. For inverted PWM the output will have the opposite logic values. If
OCRnA is used to define the TOP value (WGMn3:0 = 11) and COMnA1:0 = 1, the OCnA output
will toggle with a 50% duty cycle.
Phase and Frequency
Correct PWM Mode
The phase and frequency correct Pulse Width Modulation, or phase and frequency correct PWM
mode (WGMn3:0 = 8 or 9) provides a high resolution phase and frequency correct PWM wave-
form generation option. The phase and frequency correct PWM mode is, like the phase correct
PWM mode, based on a dual-slope operation. The counter counts repeatedly from BOTTOM
(0x0000) to TOP and then from TOP to BOTTOM. In non-inverting Compare Output mode, the
Output Compare (OCnx) is cleared on the Compare Match between TCNTn and OCRnx while
up-counting, and set on the Compare Match while down-counting. In inverting Compare Output
mode, the operation is inverted. The dual-slope operation gives a lower maximum operation fre-
quency compared to the single-slope operation. However, due to the symmetric feature of the
dual-slope PWM modes, these modes are preferred for motor control applications.
The main difference between the phase correct, and the phase and frequency correct PWM
mode is the time the OCRnx Register is updated by the OCRnx Buffer Register, (see Figure 53
and Figure 54).
fOCnxPCPWM
fclk_I/O
2NTOP⋅⋅
----------------------------=
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ATmega162/V
The PWM resolution for the phase and frequency correct PWM mode can be defined by either
ICRn or OCRnA. The minimum resolution allowed is 2-bit (ICRn or OCRnA set to 0x0003), and
the maximum resolution is 16-bit (ICRn or OCRnA set to MAX). The PWM resolution in bits can
be calculated using the following equation:
In phase and frequency correct PWM mode the counter is incremented until the counter value
matches either the value in ICRn (WGMn3:0 = 8), or the value in OCRnA (WGMn3:0 = 9). The
counter has then reached the TOP and changes the count direction. The TCNTn value will be
equal to TOP for one timer clock cycle. The timing diagram for the phase correct and frequency
correct PWM mode is shown on Figure 54. The figure shows phase and frequency correct PWM
mode when OCRnA or ICRn is used to define TOP. The TCNTn value is in the timing diagram
shown as a histogram for illustrating the dual-slope operation. The diagram includes non-
inverted and inverted PWM outputs. The small horizontal line marks on the TCNTn slopes repre-
sent compare matches between OCRnx and TCNTn. The OCnx Interrupt Flag will be set when a
Compare Match occurs.
Figure 54. Phase and Frequency Correct PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOVn) is set at the same timer clock cycle as the OCRnx
Registers are updated with the double buffer value (at BOTTOM). When either OCRnA or ICRn
is used for defining the TOP value, the OCnA or ICFn Flag set when TCNTn has reached TOP.
The Interrupt Flags can then be used to generate an interrupt each time the counter reaches the
TOP or BOTTOM value.
When changing the TOP value the program must ensure that the new TOP value is higher or
equal to the value of all of the compare registers. If the TOP value is lower than any of the com-
pare registers, a Compare Match will never occur between the TCNTn and the OCRnx.
As Figure 54 shows the output generated is, in contrast to the phase correct mode, symmetrical
in all periods. Since the OCRnx Registers are updated at BOTTOM, the length of the rising and
the falling slopes will always be equal. This gives symmetrical output pulses and is therefore fre-
quency correct.
RPFCPWM
TOP 1+()log
2()log
-----------------------------------=
OCRnx/TOP Update and
TOVn Interrupt Flag Set
(Interrupt on Bottom)
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set
(Interrupt on TOP)
1 2 3 4
TCNTn
Period
OCnx
OCnx
(COMnx1:0 = 2)
(COMnx1:0 = 3)
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Using the ICRn Register for defining TOP works well when using fixed TOP values. By using
ICRn, the OCRnA Register is free to be used for generating a PWM output on OCnA. However,
if the base PWM frequency is actively changed by changing the TOP value, using the OCRnA as
TOP is clearly a better choice due to its double buffer feature.
In phase and frequency correct PWM mode, the compare units allow generation of PWM wave-
forms on the OCnx pins. Setting the COMnx1:0 bits to two will produce a non-inverted PWM and
an inverted PWM output can be generated by setting the COMnx1:0 to three (See Table 55 on
page 129). The actual OCnx value will only be visible on the port pin if the data direction for the
port pin is set as output (DDR_OCnx). The PWM waveform is generated by setting (or clearing)
the OCnx Register at the Compare Match between OCRnx and TCNTn when the counter incre-
ments, and clearing (or setting) the OCnx Register at Compare Match between OCRnx and
TCNTn when the counter decrements. The PWM frequency for the output when using phase
and frequency correct PWM can be calculated by the following equation:
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024). For Timer/Counter3 also
prescaler factors 16 and 32 are available.
The extreme values for the OCRnx Register represents special cases when generating a PWM
waveform output in the phase correct PWM mode. If the OCRnx is set equal to BOTTOM the
output will be continuously low and if set equal to TOP the output will be set to high for non-
inverted PWM mode. For inverted PWM the output will have the opposite logic values. If OCRnA
is used to define the TOP value (WGMn3:0 = 9) and COMnA1:0 = 1, the OCnA output will toggle
with a 50% duty cycle.
fOCnxPFCPWM
fclk_I/O
2NTOP⋅⋅
----------------------------=
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Timer/Counter
Timing Diagrams
The Timer/Counter is a synchronous design and the timer clock (clkTn) is therefore shown as a
clock enable signal in the following figures. The figures include information on when Interrupt
Flags are set, and when the OCRnx Register is updated with the OCRnx buffer value (only for
modes utilizing double buffering). Figure 55 shows a timing diagram for the setting of OCFnx.
Figure 55. Timer/Counter Timing Diagram, Setting of OCFnx, no Prescaling
Figure 56 shows the same timing data, but with the prescaler enabled.
Figure 56. Timer/Counter Timing Diagram, Setting of OCFnx, with Prescaler (fclk_I/O/8)
Figure 57 shows the count sequence close to TOP in various modes. When using phase and
frequency correct PWM mode the OCRnx Register is updated at BOTTOM. The timing diagrams
will be the same, but TOP should be replaced by BOTTOM, TOP-1 by BOTTOM+1 and so on.
The same renaming applies for modes that set the TOVn Flag at BOTTOM.
clk
Tn
(clk
I/O
/1)
OCFnx
clk
I/O
OCRnx
TCNTn
OCRnx Value
OCRnx - 1 OCRnx OCRnx + 1 OCRnx + 2
OCFnx
OCRnx
TCNTn
OCRnx Value
OCRnx - 1 OCRnx OCRnx + 1 OCRnx + 2
clkI/O
clkTn
(clkI/O/8)
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ATmega162/V
Figure 57. Timer/Counter Timing Diagram, no Prescaling
Figure 58 shows the same timing data, but with the prescaler enabled.
Figure 58. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
TOVn
(FPWM)
and ICFn
(if used
as TOP)
OCRnx
(Update at TOP)
TCNTn
(CTC and FPWM)
TCNTn
(PC and PFC PWM) TOP - 1 TOP TOP - 1 TOP - 2
Old OCRnx Value New OCRnx Value
TOP - 1 TOP BOTTOM BOTTOM + 1
clkTn
(clkI/O/1)
clkI/O
TOVn (FPWM)
and ICFn (if used
as TOP)
OCRnx
(Update at TOP)
TCNTn
(CTC and FPWM)
TCNTn
(PC and PFC PWM) TOP - 1 TOP TOP - 1 TOP - 2
Old OCRnx Value New OCRnx Value
TOP - 1 TOP BOTTOM BOTTOM + 1
clkI/O
clkTn
(clk
I/O
/8)
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ATmega162/V
16-bit
Timer/Counter
Register
Description
Timer/Counter1
Control Register A –
TCCR1A
Timer/Counter3
Control Register A –
TCCR3A
• Bit 7:6 – COMnA1:0: Compare Output Mode for channel A
• Bit 5:4 – COMnB1:0: Compare Output Mode for channel B
The COMnA1:0 and COMnB1:0 control the Output Compare pins (OCnA and OCnB respec-
tively) behavior. If one or both of the COMnA1:0 bits are written to one, the OCnA output
overrides the normal port functionality of the I/O pin it is connected to. If one or both of the
COMnB1:0 bit are written to one, the OCnB output overrides the normal port functionality of the
I/O pin it is connected to. However, note that the Data Direction Register (DDR) bit correspond-
ing to the OCnA or OCnB pin must be set in order to enable the output driver.
When the OCnA or OCnB is connected to the pin, the function of the COMnx1:0 bits is depen-
dent of the WGMn3:0 bits setting. Table 53 shows the COMnx1:0 bit functionality when the
WGMn3:0 bits are set to a normal or a CTC mode (non-PWM).
Bit 76543210
COM1A1 COM1A0 COM1B1 COM1B0 FOC1A FOC1B WGM11 WGM10 TCCR1A
Read/Write R/W R/W R/W R/W W W R/W R/W
Initial Value00000000
Bit 76543210
COM3A1 COM3A0 COM3B1 COM3B0 FOC3A FOC3B WGM31 WGM30 TCCR3A
Read/Write R/W R/W R/W R/W W W R/W R/W
Initial Value00000000
Table 53. Compare Output Mode, non-PWM
COMnA1/
COMnB1
COMnA0/
COMnB0 Description
0 0 Normal port operation, OCnA/OCnB disconnected.
0 1 Toggle OCnA/OCnB on Compare Match.
1 0 Clear OCnA/OCnB on Compare Match (Set output to low level).
1 1 Set OCnA/OCnB on Compare Match (Set output to high level).
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Table 54 shows the COMnx1:0 bit functionality when the WGMn3:0 bits are set to the fast PWM
mode.
Note: 1. A special case occurs when OCRnA/OCRnB equals TOP and COMnA1/COMnB1 is set. In
this case the Compare Match is ignored, but the set or clear is done at TOP. See “Fast PWM
Mode” on page 120. for more details.
Table 55 shows the COMnx1:0 bit functionality when the WGMn3:0 bits are set to the phase cor-
rect or the phase and frequency correct, PWM mode.
Note: 1. A special case occurs when OCRnA/OCRnB equals TOP and COMnA1/COMnB1 is set. See
“Phase Correct PWM Mode” on page 122. for more details.
• Bit 3 – FOCnA: Force Output Compare for channel A
• Bit 2 – FOCnB: Force Output Compare for channel B
The FOCnA/FOCnB bits are only active when the WGMn3:0 bits specifies a non-PWM mode.
However, for ensuring compatibility with future devices, these bits must be set to zero when
TCCRnA is written when operating in a PWM mode. When writing a logical one to the
FOCnA/FOCnB bit, an immediate Compare Match is forced on the Waveform Generation unit.
The OCnA/OCnB output is changed according to its COMnx1:0 bits setting. Note that the
FOCnA/FOCnB bits are implemented as strobes. Therefore it is the value present in the
COMnx1:0 bits that determine the effect of the forced compare.
A FOCnA/FOCnB strobe will not generate any interrupt nor will it clear the timer in Clear Timer
on Compare match (CTC) mode using OCRnA as TOP.
The FOCnA/FOCnB bits are always read as zero.
Table 54. Compare Output Mode, Fast PWM(1)
COMnA1/
COMnB1
COMnA0/
COMnB0 Description
0 0 Normal port operation, OCnA/OCnB disconnected.
0 1 WGMn3:0 = 15: Toggle OCnA on Compare Match, OCnB
disconnected (normal port operation). For all other WGMn
settings, normal port operation, OCnA/OCnB disconnected.
1 0 Clear OCnA/OCnB on Compare Match, set OCnA/OCnB at TOP.
1 1 Set OCnA/OCnB on Compare Match, clear OCnA/OCnB at TOP.
Table 55. Compare Output Mode, Phase Correct and Phase and Frequency Correct PWM(1)
COMnA1/
COMnB1
COMnA0
COMnB0 Description
0 0 Normal port operation, OCnA/OCnB disconnected.
0 1 WGMn3:0 = 9 or 14: Toggle OCnA on Compare Match, OCnB
disconnected (normal port operation). For all other WGMn
settings, normal port operation, OCnA/OCnB disconnected.
1 0 Clear OCnA/OCnB on Compare Match when up-counting. Set
OCnA/OCnB on Compare Match when down-counting.
1 1 Set OCnA/OCnB on Compare Match when up-counting. Clear
OCnA/OCnB on Compare Match when down-counting.
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• Bit 1:0 – WGMn1:0: Waveform Generation Mode
Combined with the WGMn3:2 bits found in the TCCRnB Register, these bits control the counting
sequence of the counter, the source for maximum (TOP) counter value, and what type of wave-
form generation to be used, see Table 56. Modes of operation supported by the Timer/Counter
unit are: Normal mode (counter), Clear Timer on Compare match (CTC) mode, and three types
of Pulse Width Modulation (PWM) modes. (See “Modes of Operation” on page 118.)
Note: 1. The CTCn and PWMn1:0 bit definition names are obsolete. Use the WGMn2:0 definitions. However, the functionality and
location of these bits are compatible with previous versions of the timer.
Table 56. Waveform Generation Mode Bit Description(1)
Mode WGMn3
WGMn2
(CTCn)
WGMn1
(PWMn1)
WGMn0
(PWMn0) Timer/Counter Mode of Operation TOP
Update of
OCRnx at
TOVn Flag
Set on
0 0 0 0 0 Normal 0xFFFF Immediate MAX
1 0 0 0 1 PWM, Phase Correct, 8-bit 0x00FF TOP BOTTOM
2 0 0 1 0 PWM, Phase Correct, 9-bit 0x01FF TOP BOTTOM
3 0 0 1 1 PWM, Phase Correct, 10-bit 0x03FF TOP BOTTOM
4 0 1 0 0 CTC OCRnA Immediate MAX
5 0 1 0 1 Fast PWM, 8-bit 0x00FF TOP TOP
6 0 1 1 0 Fast PWM, 9-bit 0x01FF TOP TOP
7 0 1 1 1 Fast PWM, 10-bit 0x03FF TOP TOP
8 1 0 0 0 PWM, Phase and Frequency Correct ICRn BOTTOM BOTTOM
9 1 0 0 1 PWM, Phase and Frequency Correct OCRnA BOTTOM BOTTOM
10 1 0 1 0 PWM, Phase Correct ICRn TOP BOTTOM
11 1 0 1 1 PWM, Phase Correct OCRnA TOP BOTTOM
12 1 1 0 0 CTC ICRn Immediate MAX
13 1 1 0 1 Reserved – – –
14 1 1 1 0 Fast PWM ICRn TOP TOP
15 1 1 1 1 Fast PWM OCRnA TOP TOP
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ATmega162/V
Timer/Counter1
Control Register B –
TCCR1B
Timer/Counter3
Control Register B –
TCCR3B
• Bit 7 – ICNCn: Input Capture Noise Canceler
Setting this bit (to one) activates the Input Capture noise canceler. When the noise canceler is
activated, the input from the Input Capture pin (ICPn) is filtered. The filter function requires four
successive equal valued samples of the ICPn pin for changing its output. The Input Capture is
therefore delayed by four Oscillator cycles when the noise canceler is enabled.
• Bit 6 – ICESn: Input Capture Edge Select
This bit selects which edge on the Input Capture pin (ICPn) that is used to trigger a capture
event. When the ICESn bit is written to zero, a falling (negative) edge is used as trigger, and
when the ICESn bit is written to one, a rising (positive) edge will trigger the capture.
When a capture is triggered according to the ICESn setting, the counter value is copied into the
Input Capture Register (ICRn). The event will also set the Input Capture Flag (ICFn), and this
can be used to cause an Input Capture Interrupt, if this interrupt is enabled.
When the ICRn is used as TOP value (see description of the WGMn3:0 bits located in the
TCCRnA and the TCCRnB Register), the ICPn is disconnected and consequently the Input Cap-
ture function is disabled.
• Bit 5 – Reserved Bit
This bit is reserved for future use. For ensuring compatibility with future devices, this bit must be
written to zero when TCCRnB is written.
• Bit 4:3 – WGMn3:2: Waveform Generation Mode
See TCCRnA Register description.
Bit 76543210
ICNC1 ICES1 – WGM13 WGM12 CS12 CS11 CS10 TCCR1B
Read/Write R/W R/W R R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
ICNC3 ICES3 – WGM33 WGM32 CS32 CS31 CS30 TCCR3B
Read/Write R/W R/W R R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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• Bit 2:0 – CSn2:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter, see Figure
55 and Figure 56.
If external pin modes are used for the Timer/Counter1, transitions on the T1 pin will clock the
counter even if the pin is configured as an output. This feature allows software control of the
counting..
Table 57. Clock Select Bit Description Timer/Counter1
CS12 CS11 CS10 Description
0 0 0 No clock source. (Timer/Counter stopped).
001clk
I/O/1 (No prescaling)
010clk
I/O/8 (From prescaler)
011clk
I/O/64 (From prescaler)
100clk
I/O/256 (From prescaler)
101clk
I/O/1024 (From prescaler)
1 1 0 External clock source on T1 pin. Clock on falling edge.
1 1 1 External clock source on T1 pin. Clock on rising edge.
Table 58. Clock Select Bit Description Timer/Counter3
CS32 CS31 CS30 Description
0 0 0 No clock source. (Timer/Counter stopped).
001clk
I/O / 1 (No prescaling)
010clk
I/O / 8 (From prescaler).
011clk
I/O / 64 (From prescaler).
100clk
I/O / 256 (From prescaler).
101clk
I/O / 1024 (From prescaler).
110clk
I/O / 16 (From prescaler).
111clk
I/O / 32 (From prescaler).
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Timer/Counter1 –
TCNT1H and TCNT1L
Timer/Counter3 –
TCNT3H and TCNT3L
The two Timer/Counter I/O locations (TCNTnH and TCNTnL, combined TCNTn) give direct
access, both for read and for write operations, to the Timer/Counter unit 16-bit counter. To
ensure that both the high and low bytes are read and written simultaneously when the CPU
accesses these registers, the access is performed using an 8-bit temporary high byte register
(TEMP). This temporary register is shared by all the other 16-bit registers. See “Accessing 16-bit
Registers” on page 109.
Modifying the counter (TCNTn) while the counter is running introduces a risk of missing a Com-
pare Match between TCNTn and one of the OCRnx Registers.
Writing to the TCNTn Register blocks (removes) the Compare Match on the following timer clock
for all compare units.
Output Compare
Register 1 A –
OCR1AH and OCR1AL
Output Compare
Register 1 B –
OCR1BH and OCR1BL
Output Compare
Register 3 A –
OCR3AH and OCR3AL
Output Compare
Register 3 B –
OCR3BH and OCR3BL
Bit 76543210
TCNT1[15:8] TCNT1H
TCNT1[7:0] TCNT1L
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
TCNT3[15:8] TCNT3H
TCNT3[7:0] TCNT3L
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
OCR1A[15:8] OCR1AH
OCR1A[7:0] OCR1AL
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
OCR1B[15:8] OCR1BH
OCR1B[7:0] OCR1BL
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
OCR3A[15:8] OCR3AH
OCR3A[7:0] OCR3AL
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
OCR3B[15:8] OCR3BH
OCR3B[7:0] OCR3BL
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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The Output Compare Registers contain a 16-bit value that is continuously compared with the
counter value (TCNTn). A match can be used to generate an output compare interrupt, or to
generate a waveform output on the OCnx pin.
The Output Compare Registers are 16-bit in size. To ensure that both the high and low bytes are
written simultaneously when the CPU writes to these registers, the access is performed using an
8-bit temporary high byte register (TEMP). This temporary register is shared by all the other 16-
bit registers. See “Accessing 16-bit Registers” on page 109.
Input Capture Register
1 – ICR1H and ICR1L
Input Capture Register
3 – ICR3H and ICR3L
The Input Capture is updated with the counter (TCNTn) value each time an event occurs on the
ICPn pin (or optionally on the Analog Comparator output for Timer/Counter1). The Input Capture
can be used for defining the counter TOP value.
The Input Capture Register is 16-bit in size. To ensure that both the high and low bytes are read
simultaneously when the CPU accesses these registers, the access is performed using an 8-bit
temporary high byte register (TEMP). This temporary register is shared by all the other 16-bit
registers. See “Accessing 16-bit Registers” on page 109.
Timer/Counter
Interrupt Mask
Register – TIMSK(1)
Note: 1. This register contains interrupt control bits for several Timer/Counters, but only Timer1 bits are
described in this section. The remaining bits are described in their respective Timer sections.
• Bit 7 – TOIE1: Timer/Counter1, Overflow Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter1 overflow interrupt is enabled. The corresponding Interrupt Vector
(See “Interrupts” on page 57.) is executed when the TOV1 Flag, located in TIFR, is set.
• Bit 6 – OCIE1A: Timer/Counter1, Output Compare A Match Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter1 Output Compare A Match interrupt is enabled. The corresponding
Interrupt Vector (See “Interrupts” on page 57.) is executed when the OCF1A Flag, located in
TIFR, is set.
• Bit 5 – OCIE1B: Timer/Counter1, Output Compare B Match Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter1 Output Compare B Match interrupt is enabled. The corresponding
Bit 76543210
ICR1[15:8] ICR1H
ICR1[7:0] ICR1L
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
ICR3[15:8] ICR3H
ICR3[7:0] ICR3L
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
TOIE1 OCIE1A OCIE1B OCIE2 TICIE1 TOIE2 TOIE0 OCIE0 TIMSK
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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Interrupt Vector (See “Interrupts” on page 57.) is executed when the OCF1B Flag, located in
TIFR, is set.
• Bit 3 – TICIE1: Timer/Counter1, Input Capture Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter1 Input Capture interrupt is enabled. The corresponding Interrupt
Vector (See “Interrupts” on page 57.) is executed when the ICF1 Flag, located in TIFR, is set.
Extended
Timer/Counter
Interrupt Mask
Register – ETIMSK(1)
Note: 1. This register contains interrupt control bits for several Timer/Counters, but only Timer3 bits are
described in this section. The remaining bits are described in their respective Timer sections.
• Bit 5 – TICIE3: Timer/Counter3, Input Capture Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter3 Input Capture interrupt is enabled. The corresponding Interrupt
Vector (See “Interrupts” on page 57.) is executed when the ICF3 Flag, located in TIFR, is set.
• Bit 4 – OCIE3A: Timer/Counter3, Output Compare A Match Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter3 Output Compare A Match interrupt is enabled. The corresponding
Interrupt Vector (See “Interrupts” on page 57.) is executed when the OCF3A Flag, located in
TIFR, is set.
• Bit 3 – OCIE3B: Timer/Counter3, Output Compare B Match Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter3 Output Compare B Match interrupt is enabled. The corresponding
Interrupt Vector (See “Interrupts” on page 57.) is executed when the OCF3B Flag, located in
TIFR, is set.
• Bit 2 – TOIE3: Timer/Counter3, Overflow Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter3 overflow interrupt is enabled. The corresponding Interrupt Vector
(See “Interrupts” on page 57.) is executed when the TOV3 Flag, located in TIFR, is set.
Timer/Counter
Interrupt Flag Register
– TIFR(1)
Note: 1. This register contains flag bits for several Timer/Counters, but only Timer1 bits are described
in this section. The remaining bits are described in their respective Timer sections.
• Bit 7 – TOV1: Timer/Counter1, Overflow Flag
The setting of this flag is dependent of the WGMn3:0 bits setting. In Normal and CTC modes,
the TOV1 Flag is set when the timer overflows. Refer to Table 56 on page 130 for the TOV1 Flag
behavior when using another WGMn3:0 bit setting.
Bit 7 6 5 4 3 2 1 0
TICIE3 OCIE3A OCIE3B TOIE3 ––ETIMSK
Read/Write R R R/W R/W R/W R/W R R
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
TOV1 OCF1A OC1FB OCF2 ICF1 TOV2 TOV0 OCF0 TIFR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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TOV1 is automatically cleared when the Timer/Counter1 Overflow Interrupt Vector is executed.
Alternatively, TOV1 can be cleared by writing a logic one to its bit location.
• Bit 6 – OCF1A: Timer/Counter1, Output Compare A Match Flag
This flag is set in the timer clock cycle after the counter (TCNT1) value matches the Output
Compare Register A (OCR1A).
Note that a Forced Output Compare (FOC1A) strobe will not set the OCF1A Flag.
OCF1A is automatically cleared when the Output Compare Match A Interrupt Vector is exe-
cuted. Alternatively, OCF1A can be cleared by writing a logic one to its bit location.
• Bit 5 – OCF1B: Timer/Counter1, Output Compare B Match Flag
This flag is set in the timer clock cycle after the counter (TCNT1) value matches the Output
Compare Register B (OCR1B).
Note that a Forced Output Compare (FOC1B) strobe will not set the OCF1B Flag.
OCF1B is automatically cleared when the Output Compare Match B Interrupt Vector is exe-
cuted. Alternatively, OCF1B can be cleared by writing a logic one to its bit location.
• Bit 3 – ICF1: Timer/Counter1, Input Capture Flag
This flag is set when a capture event occurs on the ICP1 pin. When the Input Capture Register
(ICR1) is set by the WGMn3:0 to be used as the TOP value, the ICF1 Flag is set when the coun-
ter reaches the TOP value.
ICF1 is automatically cleared when the Input Capture Interrupt Vector is executed. Alternatively,
ICF1 can be cleared by writing a logic one to its bit location.
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Extended
Timer/Counter
Interrupt Flag Register
– ETIFR(1)
Note: 1. This register contains flag bits for several Timer/Counters, but only Timer3 bits are described
in this section. The remaining bits are described in their respective Timer sections.
• Bit 5 – ICF3: Timer/Counter3, Input Capture Flag
This flag is set when a capture event occurs on the ICP3 pin. When the Input Capture Register
(ICR3) is set by the WGMn3:0 to be used as the TOP value, the ICF3 Flag is set when the coun-
ter reaches the TOP value.
ICF3 is automatically cleared when the Input Capture Interrupt Vector is executed. Alternatively,
ICF3 can be cleared by writing a logic one to its bit location.
• Bit 4 – OCF3A: Timer/Counter3, Output Compare A Match Flag
This flag is set in the timer clock cycle after the counter (TCNT3) value matches the Output
Compare Register A (OCR3A).
Note that a Forced Output Compare (FOC3A) strobe will not set the OCF3A Flag.
OCF3A is automatically cleared when the Output Compare Match A Interrupt Vector is exe-
cuted. Alternatively, OCF3A can be cleared by writing a logic one to its bit location.
• Bit 3 – OCF3B: Timer/Counter3, Output Compare B Match Flag
This flag is set in the timer clock cycle after the counter (TCNT3) value matches the Output
Compare Register B (OCR3B).
Note that a Forced Output Compare (FOC3B) strobe will not set the OCF3B Flag.
OCF3B is automatically cleared when the Output Compare Match B Interrupt Vector is exe-
cuted. Alternatively, OCF3B can be cleared by writing a logic one to its bit location.
• Bit 2 – TOV3: Timer/Counter3, Overflow Flag
The setting of this flag is dependent of the WGMn3:0 bits setting. In normal and CTC modes, the
TOV3 Flag is set when the timer overflows. Refer to Table 56 on page 130 for the TOV3 Flag
behavior when using another WGMn3:0 bit setting.
TOV3 is automatically cleared when the Timer/Counter3 Overflow Interrupt Vector is executed.
Alternatively, TOV3 can be cleared by writing a logic one to its bit location.
Bit 76543210
ICF3 OCF3A OC3FB TOV3 ––ETIFR
Read/Write R R R/W R/W R/W R/W R R
Initial Value00000000
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8-bit
Timer/Counter2
with PWM and
Asynchronous
operation
Timer/Counter2 is a general purpose, single channel, 8-bit Timer/Counter module. The main
features are:
•Single Channel Counter
•Clear Timer on Compare Match (Auto Reload)
•Glitch-free, Phase Correct Pulse Width Modulator (PWM)
•Frequency Generator
•10-bit Clock Prescaler
•Overflow and Compare Match Interrupt Sources (TOV2 and OCF2)
•Allows Clocking from External 32 kHz Watch Crystal Independent of the I/O Clock
Overview A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 59. For the actual place-
ment of I/O pins, refer to “Pinout ATmega162” on page 2. CPU accessible I/O Registers,
including I/O bits and I/O pins, are shown in bold. The device-specific I/O Register and bit loca-
tions are listed in the “8-bit Timer/Counter Register Description” on page 149.
Figure 59. 8-bit Timer/Counter Block Diagram
Registers The Timer/Counter (TCNT2) and Output Compare Register (OCR2) are 8-bit registers. Interrupt
request (shorten as Int.Req.) signals are all visible in the Timer Interrupt Flag Register (TIFR).
All interrupts are individually masked with the Timer Interrupt Mask Register (TIMSK). TIFR and
TIMSK are not shown in the figure since these registers are shared by other timer units.
The Timer/Counter can be clocked internally, via the prescaler, or asynchronously clocked from
the TOSC1/2 pins, as detailed later in this section. The asynchronous operation is controlled by
Timer/Counter
DATABUS
=
TCNTn
Waveform
Generation OCn
= 0
Control Logic
=
0xFF
TOPBOTTOM
count
clear
direction
TOVn
(Int.Req.)
OCn
(Int.Req.)
Synchronization Unit
OCRn
TCCRn
ASSRn
Status flags
clkI/O
clkASY
Synchronized Status flags
asynchronous mode
select (ASn)
TOSC1
T/C
Oscillator
TOSC2
Prescaler
clkTn
clkI/O
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the Asynchronous Status Register (ASSR). The Clock Select logic block controls which clock
source the Timer/Counter uses to increment (or decrement) its value. The Timer/Counter is inac-
tive when no clock source is selected. The output from the clock select logic is referred to as the
Timer Clock (clkT2).
The double buffered Output Compare Register (OCR2) is compared with the Timer/Counter
value at all times. The result of the compare can be used by the waveform generator to generate
a PWM or variable frequency output on the Output Compare Pin (OC2). See “Output Compare
Unit” on page 140. for details. The Compare Match event will also set the Compare Flag (OCF2)
which can be used to generate an output compare interrupt request.
Definitions Many register and bit references in this document are written in general form. A lower case “n”
replaces the Timer/Counter number, in this case 2. However, when using the register or bit
defines in a program, the precise form must be used i.e., TCNT2 for accessing Timer/Counter2
counter value and so on.
The definitions in Table 59 are also used extensively throughout the section.
Timer/Counter
Clock Sources
The Timer/Counter can be clocked by an internal synchronous or an external asynchronous
clock source. The clock source clkT2 is by default equal to the MCU clock, clkI/O. When the AS2
bit in the ASSR Register is written to logic one, the clock source is taken from the Timer/Counter
Oscillator connected to TOSC1 and TOSC2. For details on asynchronous operation, see “Asyn-
chronous Status Register – ASSR” on page 152. For details on clock sources and prescaler, see
“Timer/Counter Prescaler” on page 156.
Table 59. Definitions
BOTTOM The counter reaches the BOTTOM when it becomes zero (0x00).
MAX The counter reaches its MAXimum when it becomes 0xFF (decimal 255).
TOP The counter reaches the TOP when it becomes equal to the highest
value in the count sequence. The TOP value can be assigned to be the
fixed value 0xFF (MAX) or the value stored in the OCR2 Register. The
assignment is dependent on the mode of operation.
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Counter Unit The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure
60 shows a block diagram of the counter and its surrounding environment.
Figure 60. Counter Unit Block Diagram
Signal description (internal signals):
count Increment or decrement TCNT2 by 1.
direction Selects between increment and decrement.
clear Clear TCNT2 (set all bits to zero).
clkT2 Timer/Counter clock.
top Signalizes that TCNT2 has reached maximum value.
bottom Signalizes that TCNT2 has reached minimum value (zero).
Depending on the mode of operation used, the counter is cleared, incremented, or decremented
at each timer clock (clkT2). clkT2 can be generated from an external or internal clock source,
selected by the Clock Select bits (CS22:0). When no clock source is selected (CS22:0 = 0) the
timer is stopped. However, the TCNT2 value can be accessed by the CPU, regardless of
whether clkT2 is present or not. A CPU write overrides (has priority over) all counter clear or
count operations.
The counting sequence is determined by the setting of the WGM21 and WGM20 bits located in
the Timer/Counter Control Register (TCCR2). There are close connections between how the
counter behaves (counts) and how waveforms are generated on the Output Compare output
OC2. For more details about advanced counting sequences and waveform generation, see
“Modes of Operation” on page 143.
The Timer/Counter Overflow Flag (TOV2) is set according to the mode of operation selected by
the WGM21:0 bits. TOV2 can be used for generating a CPU interrupt.
Output Compare
Unit
The 8-bit comparator continuously compares TCNT2 with the Output Compare Register
(OCR2). Whenever TCNT2 equals OCR2, the comparator signals a match. A match will set the
Output Compare Flag (OCF2) at the next timer clock cycle. If enabled (OCIE2 = 1), the Output
Compare Flag generates an output compare interrupt. The OCF2 Flag is automatically cleared
when the interrupt is executed. Alternatively, the OCF2 Flag can be cleared by software by writ-
ing a logical one to its I/O bit location. The waveform generator uses the match signal to
generate an output according to operating mode set by the WGM21:0 bits and Compare Output
mode (COM21:0) bits. The max and bottom signals are used by the waveform generator for han-
dling the special cases of the extreme values in some modes of operation (“Modes of Operation”
on page 143).
Figure 61 shows a block diagram of the output compare unit.
DATA BUS
TCNTn Control Logic
count
TOVn
(Int.Req.)
topbottom
direction
clear
TOSC1
T/C
Oscillator
TOSC2
Prescaler
clk
I/O
clk
Tn
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Figure 61. Output Compare Unit, Block Diagram
The OCR2 Register is double buffered when using any of the Pulse Width Modulation (PWM)
modes. For the normal and Clear Timer on Compare (CTC) modes of operation, the double buff-
ering is disabled. The double buffering synchronizes the update of the OCR2 Compare Register
to either top or bottom of the counting sequence. The synchronization prevents the occurrence
of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.
The OCR2 Register access may seem complex, but this is not case. When the double buffering
is enabled, the CPU has access to the OCR2 Buffer Register, and if double buffering is disabled
the CPU will access the OCR2 directly.
Force Output
Compare
In non-PWM waveform generation modes, the match output of the comparator can be forced by
writing a one to the Force Output Compare (FOC2) bit. Forcing Compare Match will not set the
OCF2 Flag or reload/clear the timer, but the OC2 pin will be updated as if a real Compare Match
had occurred (the COM21:0 bits settings define whether the OC2 pin is set, cleared or toggled).
Compare Match
Blocking by TCNT2
Write
All CPU write operations to the TCNT2 Register will block any Compare Match that occurs in the
next timer clock cycle, even when the timer is stopped. This feature allows OCR2 to be initialized
to the same value as TCNT2 without triggering an interrupt when the Timer/Counter clock is
enabled.
Using the Output
Compare Unit
Since writing TCNT2 in any mode of operation will block all compare matches for one timer clock
cycle, there are risks involved when changing TCNT2 when using the output compare channel,
independently of whether the Timer/Counter is running or not. If the value written to TCNT2
equals the OCR2 value, the Compare Match will be missed, resulting in incorrect Waveform
Generation. Similarly, do not write the TCNT2 value equal to BOTTOM when the counter is
down-counting.
OCFn (Int.Req.)
= (8-bit Comparator )
OCRn
OCxy
DATA B US
TCNTn
WGMn1:0
Waveform Generator
top
FOCn
COMn1:0
bottom
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The Setup of the OC2 should be performed before setting the Data Direction Register for the
port pin to output. The easiest way of setting the OC2 value is to use the Force Output Compare
(FOC2) strobe bit in Normal mode. The OC2 Register keeps its value even when changing
between Waveform Generation modes.
Be aware that the COM21:0 bits are not double buffered together with the compare value.
Changing the COM21:0 bits will take effect immediately.
Compare Match
Output Unit
The Compare Output mode (COM21:0) bits have two functions. The waveform generator uses
the COM21:0 bits for defining the Output Compare (OC2) state at the next Compare Match.
Also, the COM21:0 bits control the OC2 pin output source. Figure 62 shows a simplified sche-
matic of the logic affected by the COM21:0 bit setting. The I/O Registers, I/O bits, and I/O pins in
the figure are shown in bold. Only the parts of the general I/O Port Control Registers (DDR and
PORT) that are affected by the COM21:0 bits are shown. When referring to the OC2 state, the
reference is for the internal OC2 Register, not the OC2 pin.
Figure 62. Compare Match Output Unit, Schematic
The general I/O port function is overridden by the Output Compare (OC2) from the waveform
generator if either of the COM21:0 bits are set. However, the OC2 pin direction (input or output)
is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction Regis-
ter bit for the OC2 pin (DDR_OC2) must be set as output before the OC2 value is visible on the
pin. The port override function is independent of the Waveform Generation mode.
The design of the Output Compare pin logic allows initialization of the OC2 state before the out-
put is enabled. Note that some COM21:0 bit settings are reserved for certain modes of
operation. See “8-bit Timer/Counter Register Description” on page 149.
PORT
DDR
DQ
DQ
OCn
Pin
OCn
DQ
Waveform
Generator
COMn1
COMn0
0
1
DATA B US
FOCn
clkI/O
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Compare Output Mode
and Waveform
Generation
The Waveform Generator uses the COM21:0 bits differently in Normal, CTC, and PWM modes.
For all modes, setting the COM21:0 = 0 tells the Waveform Generator that no action on the OC2
Register is to be performed on the next Compare Match. For compare output actions in the non-
PWM modes refer to Table 61 on page 150. For fast PWM mode, refer to Table 62 on page 150,
and for phase correct PWM refer to Table 63 on page 150.
A change of the COM21:0 bits state will have effect at the first Compare Match after the bits are
written. For non-PWM modes, the action can be forced to have immediate effect by using the
FOC2 strobe bits.
Modes of
Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, is
defined by the combination of the Waveform Generation mode (WGM21:0) and Compare Output
mode (COM21:0) bits. The Compare Output mode bits do not affect the counting sequence,
while the Waveform Generation mode bits do. The COM21:0 bits control whether the PWM out-
put generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes
the COM21:0 bits control whether the output should be set, cleared, or toggled at a Compare
Match (See “Compare Match Output Unit” on page 142.).
For detailed timing information refer to “Timer/Counter Timing Diagrams” on page 147.
Normal Mode The simplest mode of operation is the Normal mode (WGM21:0 = 0). In this mode the counting
direction is always up (incrementing), and no counter clear is performed. The counter simply
overruns when it passes its maximum 8-bit value (TOP = 0xFF) and then restarts from the bot-
tom (0x00). In normal operation the Timer/Counter Overflow Flag (TOV2) will be set in the same
timer clock cycle as the TCNT2 becomes zero. The TOV2 Flag in this case behaves like a ninth
bit, except that it is only set, not cleared. However, combined with the timer overflow interrupt
that automatically clears the TOV2 Flag, the timer resolution can be increased by software.
There are no special cases to consider in the normal mode, a new counter value can be written
anytime.
The Output Compare unit can be used to generate interrupts at some given time. Using the Out-
put Compare to generate waveforms in Normal mode is not recommended, since this will
occupy too much of the CPU time.
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Clear Timer on
Compare Match (CTC)
Mode
In Clear Timer on Compare or CTC mode (WGM21:0 = 2), the OCR2 Register is used to manip-
ulate the counter resolution. In CTC mode the counter is cleared to zero when the counter value
(TCNT2) matches the OCR2. The OCR2 defines the top value for the counter, hence also its
resolution. This mode allows greater control of the Compare Match output frequency. It also sim-
plifies the operation of counting external events.
The timing diagram for the CTC mode is shown in Figure 63. The counter value (TCNT2)
increases until a Compare Match occurs between TCNT2 and OCR2, and then counter (TCNT2)
is cleared.
Figure 63. CTC Mode, Timing Diagram
An interrupt can be generated each time the counter value reaches the TOP value by using the
OCF2 Flag. If the interrupt is enabled, the interrupt handler routine can be used for updating the
TOP value. However, changing the TOP to a value close to BOTTOM when the counter is run-
ning with none or a low prescaler value must be done with care since the CTC mode does not
have the double buffering feature. If the new value written to OCR2 is lower than the current
value of TCNT2, the counter will miss the Compare Match. The counter will then have to count to
its maximum value (0xFF) and wrap around starting at 0x00 before the Compare Match can
occur.
For generating a waveform output in CTC mode, the OC2 output can be set to toggle its logical
level on each Compare Match by setting the Compare Output mode bits to toggle mode
(COM21:0 = 1). The OC2 value will not be visible on the port pin unless the data direction for the
pin is set to output. The waveform generated will have a maximum frequency of fOC2 = fclk_I/O/2
when OCR2 is set to zero (0x00). The waveform frequency is defined by the following equation:
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
As for the Normal mode of operation, the TOV2 Flag is set in the same timer clock cycle that the
counter counts from MAX to 0x00.
TCNTn
OCn
(Toggle)
OCn Interrupt Flag Set
1 4
Period
2 3
(COMn1:0 = 1)
fOCn
fclk_I/O
2N1OCRn+()⋅⋅
-----------------------------------------------=
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Fast PWM Mode The fast Pulse Width Modulation or fast PWM mode (WGM21:0 = 1) provides a high frequency
PWM waveform generation option. The fast PWM differs from the other PWM option by its sin-
gle-slope operation. The counter counts from BOTTOM to MAX then restarts from BOTTOM. In
non-inverting Compare Output mode, the Output Compare (OC2) is cleared on the Compare
Match between TCNT2 and OCR2, and set at BOTTOM. In inverting Compare Output mode, the
output is set on Compare Match and cleared at BOTTOM. Due to the single-slope operation, the
operating frequency of the fast PWM mode can be twice as high as the phase correct PWM
mode that uses dual-slope operation. This high frequency makes the fast PWM mode well suited
for power regulation, rectification, and DAC applications. High frequency allows physically small
sized external components (coils, capacitors), and therefore reduces total system cost.
In fast PWM mode, the counter is incremented until the counter value matches the MAX value.
The counter is then cleared at the following timer clock cycle. The timing diagram for the fast
PWM mode is shown in Figure 64. The TCNT2 value is in the timing diagram shown as a histo-
gram for illustrating the single-slope operation. The diagram includes non-inverted and inverted
PWM outputs. The small horizontal line marks on the TCNT2 slopes represent compare
matches between OCR2 and TCNT2.
Figure 64. Fast PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOV2) is set each time the counter reaches MAX. If the inter-
rupt is enabled, the interrupt handler routine can be used for updating the compare value.
In fast PWM mode, the compare unit allows generation of PWM waveforms on the OC2 pin. Set-
ting the COM21:0 bits to two will produce a non-inverted PWM and an inverted PWM output can
be generated by setting the COM21:0 to three (See Table 62 on page 150). The actual OC2
value will only be visible on the port pin if the data direction for the port pin is set as output. The
PWM waveform is generated by setting (or clearing) the OC2 Register at the Compare Match
between OCR2 and TCNT2, and clearing (or setting) the OC2 Register at the timer clock cycle
the counter is cleared (changes from MAX to BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
TCNTn
OCRn Update and
TOVn Interrupt Flag Set
1
Period
2 3
OCn
OCn
(COMn1:0 = 2)
(COMn1:0 = 3)
OCRn Interrupt Flag Set
4 5 6 7
fOCnPWM
fclk_I/O
N256⋅
------------------=
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The extreme values for the OCR2 Register represent special cases when generating a PWM
waveform output in the fast PWM mode. If the OCR2 is set equal to BOTTOM, the output will be
a narrow spike for each MAX+1 timer clock cycle. Setting the OCR2 equal to MAX will result in a
constantly high or low output (depending on the polarity of the output set by the COM21:0 bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by set-
ting OC2 to toggle its logical level on each Compare Match (COM21:0 = 1). The waveform
generated will have a maximum frequency of foc2 = fclk_I/O/2 when OCR2 is set to zero. This fea-
ture is similar to the OC2 toggle in CTC mode, except the double buffer feature of the Output
Compare unit is enabled in the fast PWM mode.
Phase Correct PWM
Mode
The phase correct PWM mode (WGM21:0 = 3) provides a high resolution phase correct PWM
waveform generation option. The phase correct PWM mode is based on a dual-slope operation.
The counter counts repeatedly from BOTTOM to MAX and then from MAX to BOTTOM. In non-
inverting Compare Output mode, the Output Compare (OC2) is cleared on the Compare Match
between TCNT2 and OCR2 while up-counting, and set on the Compare Match while down-
counting. In inverting output compare mode, the operation is inverted. The dual-slope operation
has lower maximum operation frequency than single slope operation. However, due to the sym-
metric feature of the dual-slope PWM modes, these modes are preferred for motor control
applications.
The PWM resolution for the phase correct PWM mode is fixed to eight bits. In phase correct
PWM mode the counter is incremented until the counter value matches MAX. When the counter
reaches MAX, it changes the count direction. The TCNT2 value will be equal to MAX for one
timer clock cycle. The timing diagram for the phase correct PWM mode is shown on Figure 65.
The TCNT2 value is in the timing diagram shown as a histogram for illustrating the dual-slope
operation. The diagram includes non-inverted and inverted PWM outputs. The small horizontal
line marks on the TCNT2 slopes represent compare matches between OCR2 and TCNT2.
Figure 65. Phase Correct PWM Mode, Timing Diagram
The Timer/Counter Overflow Flag (TOV2) is set each time the counter reaches BOTTOM. The
Interrupt Flag can be used to generate an interrupt each time the counter reaches the BOTTOM
value.
In phase correct PWM mode, the compare unit allows generation of PWM waveforms on the
OC2 pin. Setting the COM21:0 bits to two will produce a non-inverted PWM. An inverted PWM
output can be generated by setting the COM21:0 to three (See Table 63 on page 150). The
TOVn Interrupt Flag Set
OCn Interrupt Flag Set
1 2 3
TCNTn
Period
OCn
OCn
(COMn1:0 = 2)
(COMn1:0 = 3)
OCRn Update
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actual OC2 value will only be visible on the port pin if the data direction for the port pin is set as
output. The PWM waveform is generated by clearing (or setting) the OC2 Register at the Com-
pare Match between OCR2 and TCNT2 when the counter increments, and setting (or clearing)
the OC2 Register at Compare Match between OCR2 and TCNT2 when the counter decrements.
The PWM frequency for the output when using phase correct PWM can be calculated by the fol-
lowing equation:
The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).
The extreme values for the OCR2 Register represent special cases when generating a PWM
waveform output in the phase correct PWM mode. If the OCR2 is set equal to BOTTOM, the out-
put will be continuously low and if set equal to MAX the output will be continuously high for non-
inverted PWM mode. For inverted PWM the output will have the opposite logic values.
At the very start of period 2 in Figure 65 OCn has a transition from high to low even though there
is no Compare Match. The point of this transition is to guarantee symmetry around BOTTOM.
There are two cases that give a transition without a Compare Match.
• OCR2 changes its value from MAX, like in Figure 65. When the OCR2 value is MAX the
OCn pin value is the same as the result of a down-counting Compare Match. To ensure
symmetry around BOTTOM the OCn value at MAX must correspond to the result of an up-
counting Compare Match.
• The timer starts counting from a value higher than the one in OCR2, and for that reason
misses the Compare Match and hence the OCn change that would have happened on the
way up.
Timer/Counter
Timing Diagrams
The following figures show the Timer/Counter in synchronous mode, and the timer clock (clkT2)
is therefore shown as a clock enable signal. In asynchronous mode, clkI/O should be replaced by
the Timer/Counter Oscillator clock. The figures include information on when Interrupt Flags are
set. Figure 66 contains timing data for basic Timer/Counter operation. The figure shows the
count sequence close to the MAX value in all modes other than phase correct PWM mode.
Figure 66. Timer/Counter Timing Diagram, no Prescaling
Figure 67 shows the same timing data, but with the prescaler enabled.
fOCnPCPWM
fclk_I/O
N510⋅
------------------=
clkTn
(clkI/O/1)
TOVn
clkI/O
TCNTn
MAX - 1 MAX BOTTOM BOTTOM + 1
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Figure 67. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
Figure 68 shows the setting of OCF2 in all modes except CTC mode.
Figure 68. Timer/Counter Timing Diagram, Setting of OCF2, with Prescaler (fclk_I/O/8)
Figure 69 shows the setting of OCF2 and the clearing of TCNT2 in CTC mode.
Figure 69. Timer/Counter Timing Diagram, Clear Timer on Compare Match mode, with Pres-
caler (fclk_I/O/8)
TOVn
TCNTn
MAX - 1 MAX BOTTOM BOTTOM + 1
clk
I/O
clk
Tn
(clk
I/O
/8)
OCFn
OCRn
TCNTn
OCRn Value
OCRn - 1 OCRn OCRn + 1 OCRn + 2
clk
I/O
clk
Tn
(clkI/O/8)
OCFn
OCRn
TCNTn
(CTC)
TOP
TOP - 1 TOP BOTTOM BOTTOM + 1
clkI/O
clkTn
(clk
I/O
/8)
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8-bit
Timer/Counter
Register
Description
Timer/Counter Control
Register – TCCR2
• Bit 7 – FOC2: Force Output Compare
The FOC2 bit is only active when the WGM bits specify a non-PWM mode. However, for ensur-
ing compatibility with future devices, this bit must be set to zero when TCCR2 is written when
operating in PWM mode. When writing a logical one to the FOC2 bit, an immediate Compare
Match is forced on the Waveform Generation unit. The OC2 output is changed according to its
COM21:0 bits setting. Note that the FOC2 bit is implemented as a strobe. Therefore it is the
value present in the COM21:0 bits that determines the effect of the forced compare.
A FOC2 strobe will not generate any interrupt, nor will it clear the timer in CTC mode using
OCR2 as TOP.
The FOC2 bit is always read as zero.
• Bit 6, 3 – WGM21:0: Waveform Generation Mode
These bits control the counting sequence of the counter, the source for the maximum (TOP)
counter value, and what type of waveform generation to be used. Modes of operation supported
by the Timer/Counter unit are: Normal mode, Clear Timer on Compare match (CTC) mode, and
two types of Pulse Width Modulation (PWM) modes. See Table 60 and “Modes of Operation” on
page 143.
Note: 1. The CTC2 and PWM2 bit definition names are now obsolete. Use the WGM21:0 definitions.
However, the functionality and location of these bits are compatible with previous versions of
the timer.
Bit 76543210
FOC2 WGM20 COM21 COM20 WGM21 CS22 CS21 CS20 TCCR2
Read/Write W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Table 60. Waveform Generation Mode Bit Description(1)
Mode
WGM21
(CTC2)
WGM20
(PWM2)
Timer/Counter Mode
of Operation TOP
Update of
OCR2 at
TOV2 Flag
Set on
0 0 0 Normal 0xFF Immediate MAX
1 0 1 PWM, Phase Correct 0xFF TOP BOTTOM
2 1 0 CTC OCR2 Immediate MAX
3 1 1 Fast PWM 0xFF TOP MAX
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• Bit 5:4 – COM21:0: Compare Match Output Mode
These bits control the Output Compare pin (OC2) behavior. If one or both of the COM21:0 bits
are set, the OC2 output overrides the normal port functionality of the I/O pin it is connected to.
However, note that the Data Direction Register (DDR) bit corresponding to OC2 pin must be set
in order to enable the output driver.
When OC2 is connected to the pin, the function of the COM21:0 bits depends on the WGM21:0
bit setting. Table 61 shows the COM21:0 bit functionality when the WGM21:0 bits are set to a
normal or CTC mode (non-PWM).
Table 62 shows the COM21:0 bit functionality when the WGM21:0 bits are set to fast PWM
mode.
Note: 1. A special case occurs when OCR2 equals TOP and COM21 is set. In this case, the Compare
Match is ignored, but the set or clear is done at TOP. See “Fast PWM Mode” on page 145 for
more details.
Table 63 shows the COM21:0 bit functionality when the WGM21:0 bits are set to phase correct
PWM mode.
Note: 1. A special case occurs when OCR2 equals TOP and COM21 is set. In this case, the Compare
Match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” on page
146 for more details.
Table 61. Compare Output Mode, non-PWM Mode
COM21 COM20 Description
0 0 Normal port operation, OC2 disconnected.
0 1 Toggle OC2 on Compare Match.
1 0 Clear OC2 on Compare Match.
1 1 Set OC2 on Compare Match.
Table 62. Compare Output Mode, Fast PWM Mode(1)
COM21 COM20 Description
0 0 Normal port operation, OC2 disconnected.
01Reserved
1 0 Clear OC2 on Compare Match, set OC2 at TOP.
1 1 Set OC2 on Compare Match, clear OC2 at TOP.
Table 63. Compare Output Mode, Phase Correct PWM Mode(1)
COM21 COM20 Description
0 0 Normal port operation, OC2 disconnected.
01Reserved
1 0 Clear OC2 on Compare Match when up-counting. Set OC2 on Compare
Match when down-counting.
1 1 Set OC2 on Compare Match when up-counting. Clear OC2 on Compare
Match when down-counting.
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• Bit 2:0 – CS22:0: Clock Select
The three Clock Select bits select the clock source to be used by the Timer/Counter, see Table
64.
Timer/Counter
Register – TCNT2
The Timer/Counter Register gives direct access, both for read and write operations, to the
Timer/Counter unit 8-bit counter. Writing to the TCNT2 Register blocks (removes) the Compare
Match on the following timer clock. Modifying the counter (TCNT2) while the counter is running,
introduces a risk of missing a Compare Match between TCNT2 and the OCR2 Register.
Output Compare
Register – OCR2
The Output Compare Register contains an 8-bit value that is continuously compared with the
counter value (TCNT2). A match can be used to generate an output compare interrupt, or to
generate a waveform output on the OC2 pin.
Table 64. Clock Select Bit Description
CS22 CS21 CS20 Description
0 0 0 No clock source (Timer/Counter stopped).
001clkT2S/(No prescaling)
010clk
T2S/8 (From prescaler)
011clk
T2S/32 (From prescaler)
100clk
T2S/64 (From prescaler)
101clk
T2S/128 (From prescaler)
110clk
T2S/256 (From prescaler)
111clk
T2S/1024 (From prescaler)
Bit 76543210
TCNT2[7:0] TCNT2
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
OCR2[7:0] OCR2
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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Asynchronous
operation of the
Timer/Counter
Asynchronous Status
Register – ASSR
• Bit 3 – AS2: Asynchronous Timer/Counter2
When AS2 is written to zero, Timer/Counter2 is clocked from the I/O clock, clkI/O. When AS2 is
written to one, Timer/Counter2 is clocked from a crystal Oscillator connected to the Timer Oscil-
lator 1 (TOSC1) pin. When the value of AS2 is changed, the contents of TCNT2, OCR2, and
TCCR2 might be corrupted.
• Bit 2 – TCN2UB: Timer/Counter2 Update Busy
When Timer/Counter2 operates asynchronously and TCNT2 is written, this bit becomes set.
When TCNT2 has been updated from the temporary storage register, this bit is cleared by hard-
ware. A logical zero in this bit indicates that TCNT2 is ready to be updated with a new value.
• Bit 1 – OCR2UB: Output Compare Register2 Update Busy
When Timer/Counter2 operates asynchronously and OCR2 is written, this bit becomes set.
When OCR2 has been updated from the temporary storage register, this bit is cleared by hard-
ware. A logical zero in this bit indicates that OCR2 is ready to be updated with a new value.
• Bit 0 – TCR2UB: Timer/Counter Control Register2 Update Busy
When Timer/Counter2 operates asynchronously and TCCR2 is written, this bit becomes set.
When TCCR2 has been updated from the temporary storage register, this bit is cleared by hard-
ware. A logical zero in this bit indicates that TCCR2 is ready to be updated with a new value.
If a write is performed to any of the three Timer/Counter2 Registers while its update Busy Flag is
set, the updated value might get corrupted and cause an unintentional interrupt to occur.
The mechanisms for reading TCNT2, OCR2, and TCCR2 are different. When reading TCNT2,
the actual timer value is read. When reading OCR2 or TCCR2, the value in the temporary stor-
age register is read.
Bit 76543 2 1 0
–––– AS2 TCN2UB OCR2UB TCR2UB ASSR
Read/WriteRRRRR/WR R R
Initial Value 0 0 0 0 0 0 0 0
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Asynchronous
Operation of
Timer/Counter2
When Timer/Counter2 operates asynchronously, some considerations must be taken.
• Warning: When switching between asynchronous and synchronous clocking of
Timer/Counter2, the Timer Registers TCNT2, OCR2, and TCCR2 might be corrupted. A
safe procedure for switching clock source is:
1. Disable the Timer/Counter2 interrupts by clearing OCIE2 and TOIE2.
2. Select clock source by setting AS2 as appropriate.
3. Write new values to TCNT2, OCR2, and TCCR2.
4. To switch to asynchronous operation: Wait for TCN2UB, OCR2UB, and TCR2UB.
5. Clear the Timer/Counter2 Interrupt Flags.
6. Enable interrupts, if needed.
• The Oscillator is optimized for use with a 32.768 kHz watch crystal. Applying an external
clock to the TOSC1 pin may result in incorrect Timer/Counter2 operation. The CPU main
clock frequency must be more than four times the Oscillator frequency.
• When writing to one of the registers TCNT2, OCR2, or TCCR2, the value is transferred to a
temporary register, and latched after two positive edges on TOSC1. The user should not
write a new value before the contents of the temporary register have been transferred to its
destination. Each of the three mentioned registers have their individual temporary register,
which means that e.g., writing to TCNT2 does not disturb an OCR2 write in progress. To
detect that a transfer to the destination register has taken place, the Asynchronous Status
Register – ASSR has been implemented.
• When entering Power-save or Extended Standby mode after having written to TCNT2,
OCR2, or TCCR2, the user must wait until the written register has been updated if
Timer/Counter2 is used to wake up the device. Otherwise, the MCU will enter sleep mode
before the changes are effective. This is particularly important if the Output Compare2
interrupt is used to wake up the device, since the output compare function is disabled during
writing to OCR2 or TCNT2. If the write cycle is not finished, and the MCU enters sleep mode
before the OCR2UB bit returns to zero, the device will never receive a Compare Match
interrupt, and the MCU will not wake up.
• If Timer/Counter2 is used to wake the device up from Power-save or Extended Standby
mode, precautions must be taken if the user wants to re-enter one of these modes: The
interrupt logic needs one TOSC1 cycle to be reset. If the time between wake-up and re-
entering sleep mode is less than one TOSC1 cycle, the interrupt will not occur, and the
device will fail to wake up. If the user is in doubt whether the time before re-entering Power-
save or Extended Standby mode is sufficient, the following algorithm can be used to ensure
that one TOSC1 cycle has elapsed:
1. Write a value to TCCR2, TCNT2, or OCR2.
2. Wait until the corresponding Update Busy Flag in ASSR returns to zero.
3. Enter Power-save or Extended Standby mode.
• When the asynchronous operation is selected, the 32.768 kHz Oscillator for Timer/Counter2
is always running, except in Power-down and Standby modes. After a Power-up Reset or
wake-up from Power-down or Standby mode, the user should be aware of the fact that this
Oscillator might take as long as one second to stabilize. The user is advised to wait for at
least one second before using Timer/Counter2 after Power-up or wake-up from Power-down
or Standby mode. The contents of all Timer/Counter2 Registers must be considered lost
after a wake-up from Power-down or Standby mode due to unstable clock signal upon start-
up, no matter whether the Oscillator is in use or a clock signal is applied to the TOSC1 pin.
• Description of wake up from Power-save or Extended Standby mode when the Timer is
clocked asynchronously: When the interrupt condition is met, the wake up process is started
on the following cycle of the timer clock, that is, the Timer is always advanced by at least one
before the processor can read the counter value. After wake-up, the MCU is halted for four
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ATmega162/V
cycles, it executes the interrupt routine, and resumes execution from the instruction
following SLEEP.
• Reading of the TCNT2 Register shortly after wake-up from Power-save may give an
incorrect result. Since TCNT2 is clocked on the asynchronous TOSC clock, reading TCNT2
must be done through a register synchronized to the internal I/O clock domain.
Synchronization takes place for every rising TOSC1 edge. When waking up from Power-
save mode, and the I/O clock (clkI/O) again becomes active, TCNT2 will read as the previous
value (before entering sleep) until the next rising TOSC1 edge. The phase of the TOSC
clock after waking up from Power-save mode is essentially unpredictable, as it depends on
the wake-up time. The recommended procedure for reading TCNT2 is thus as follows:
1. Write any value to either of the registers OCR2 or TCCR2.
2. Wait for the corresponding Update Busy Flag to be cleared.
3. Read TCNT2.
• During asynchronous operation, the synchronization of the Interrupt Flags for the
Asynchronous Timer takes three processor cycles plus one timer cycle. The Timer is
therefore advanced by at least one before the processor can read the Timer value causing
the setting of the Interrupt Flag. The output compare pin is changed on the Timer clock and
is not synchronized to the processor clock.
Timer/Counter
Interrupt Mask
Register – TIMSK
• Bit 4 – OCIE2: Timer/Counter2 Output Compare Match Interrupt Enable
When the OCIE2 bit is written to one and the I-bit in the Status Register is set (one), the
Timer/Counter2 Compare Match interrupt is enabled. The corresponding interrupt is executed if
a Compare Match in Timer/Counter2 occurs, i.e., when the OCF2 bit is set in the Timer/Counter
Interrupt Flag Register – TIFR.
• Bit 2 – TOIE2: Timer/Counter2 Overflow Interrupt Enable
When the TOIE2 bit is written to one and the I-bit in the Status Register is set (one), the
Timer/Counter2 Overflow interrupt is enabled. The corresponding interrupt is executed if an
overflow in Timer/Counter2 occurs, i.e., when the TOV2 bit is set in the Timer/Counter Interrupt
Flag Register – TIFR.
Bit 76543210
TOIE1 OCIE1A OCIE1B OCIE2 TICIE1 TOIE2 TOIE0 OCIE0 TIMSK
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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Timer/Counter
Interrupt Flag Register
– TIFR
• Bit 4 – OCF2: Output Compare Flag 2
The OCF2 bit is set (one) when a Compare Match occurs between the Timer/Counter2 and the
data in OCR2 – Output Compare Register2. OCF2 is cleared by hardware when executing the
corresponding interrupt handling vector. Alternatively, OCF2 is cleared by writing a logic one to
the flag. When the I-bit in SREG, OCIE2 (Timer/Counter2 Compare Match Interrupt Enable), and
OCF2 are set (one), the Timer/Counter2 Compare Match Interrupt is executed.
• Bit 2 – TOV2: Timer/Counter2 Overflow Flag
The TOV2 bit is set (one) when an overflow occurs in Timer/Counter2. TOV2 is cleared by hard-
ware when executing the corresponding interrupt handling vector. Alternatively, TOV2 is cleared
by writing a logic one to the flag. When the SREG I-bit, TOIE2 (Timer/Counter2 Overflow Inter-
rupt Enable), and TOV2 are set (one), the Timer/Counter2 Overflow interrupt is executed. In
PWM mode, this bit is set when Timer/Counter2 changes counting direction at 0x00.
Bit 76543210
TOV1 OCF1A OC1FB OCF2 ICF1 TOV2 TOV0 OCF0 TIFR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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Timer/Counter
Prescaler
Figure 70. Prescaler for Timer/Counter2
The clock source for Timer/Counter2 is named clkT2S. clkT2S is by default connected to the main
system I/O clock clkIO. By setting the AS2 bit in ASSR, Timer/Counter2 is asynchronously
clocked from the TOSC1 pin. This enables use of Timer/Counter2 as a Real Time Counter
(RTC). When AS2 is set, pins TOSC1 and TOSC2 are disconnected from Port D. A crystal can
then be connected between the TOSC1 and TOSC2 pins to serve as an independent clock
source for Timer/Counter2. The Oscillator is optimized for use with a 32.768 kHz crystal. Apply-
ing an external clock source to TOSC1 is not recommended.
For Timer/Counter2, the possible prescaled selections are: clkT2S/8, clkT2S/32, clkT2S/64,
clkT2S/128, clkT2S/256, and clkT2S/1024. Additionally, clkT2S as well as 0 (stop) may be selected.
Setting the PSR2 bit in SFIOR resets the prescaler. This allows the user to operate with a pre-
dictable prescaler.
Special Function IO
Register – SFIOR
• Bit 1 – PSR2: Prescaler Reset Timer/Counter2
When this bit is one, the Timer/Counter2 prescaler will be reset. This bit is normally cleared
immediately by hardware. If this bit is written when Timer/Counter2 is operating in asynchronous
mode, the bit will remain one until the prescaler has been reset. The bit will not be cleared by
hardware if the TSM bit is set. Refer to the description of the “Bit 7 – TSM: Timer/Counter Syn-
chronization Mode” on page 105 for a description of the Timer/Counter Synchronization mode.
10-BIT T/C PRESCALER
TIMER/COUNTER2 CLOCK SOURCE
clkI/O clkT2S
TOSC1
AS2
CS20
CS21
CS22
clkT2S
/8
clkT2S
/64
clkT2S
/128
clkT2S
/1024
clkT2S
/256
clkT2S
/32
0
PSR2
Clear
clkT2
Bit 7 6 5 4 3 2 1 0
TSM XMBK XMM2 XMM1 XMM0 PUD PSR2 PSR310 SFIOR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Val-
ue
000 00000
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Serial
Peripheral
Interface – SPI
The Serial Peripheral Interface (SPI) allows high-speed synchronous data transfer between the
ATmega162 and peripheral devices or between several AVR devices. The ATmega162 SPI
includes the following features:
•Full-duplex, Three-wire Synchronous Data Transfer
•Master or Slave Operation
•LSB First or MSB First Data Transfer
•Seven Programmable Bit Rates
•End of Transmission Interrupt Flag
•Write Collision Flag Protection
•Wake-up from Idle Mode
•Double Speed (CK/2) Master SPI Mode
Figure 71. SPI Block Diagram(1)
Note: 1. Refer to Figure 1 on page 2, and Table 32 on page 72 for SPI pin placement.
The interconnection between Master and Slave CPUs with SPI is shown in Figure 72. The sys-
tem consists of two Shift Registers, and a Master clock generator. The SPI Master initiates the
communication cycle when pulling low the Slave Select SS pin of the desired Slave. Master and
Slave prepare the data to be sent in their respective Shift Registers, and the Master generates
the required clock pulses on the SCK line to interchange data. Data is always shifted from Mas-
ter to Slave on the Master Out – Slave In, MOSI, line, and from Slave to Master on the Master In
– Slave Out, MISO, line. After each data packet, the Master will synchronize the Slave by pulling
high the Slave Select, SS, line.
When configured as a Master, the SPI interface has no automatic control of the SS line. This
must be handled by user software before communication can start. When this is done, writing a
SPI2X
SPI2X
DIVIDER
/2/4/8/16/32/64/128
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byte to the SPI Data Register starts the SPI clock generator, and the hardware shifts the eight
bits into the Slave. After shifting one byte, the SPI clock generator stops, setting the End of
Transmission Flag (SPIF). If the SPI Interrupt Enable bit (SPIE) in the SPCR Register is set, an
interrupt is requested. The Master may continue to shift the next byte by writing it into SPDR, or
signal the end of packet by pulling high the Slave Select, SS line. The last incoming byte will be
kept in the buffer register for later use.
When configured as a Slave, the SPI interface will remain sleeping with MISO tri-stated as long
as the SS pin is driven high. In this state, software may update the contents of the SPI Data
Register, SPDR, but the data will not be shifted out by incoming clock pulses on the SCK pin
until the SS pin is driven low. As one byte has been completely shifted, the End of Transmission
Flag, SPIF is set. If the SPI interrupt enable bit, SPIE, in the SPCR Register is set, an interrupt is
requested. The Slave may continue to place new data to be sent into SPDR before reading the
incoming data. The last incoming byte will be kept in the Buffer Register for later use.
Figure 72. SPI Master-slave Interconnection
The system is single buffered in the transmit direction and double buffered in the receive direc-
tion. This means that bytes to be transmitted cannot be written to the SPI Data Register before
the entire shift cycle is completed. When receiving data, however, a received character must be
read from the SPI Data Register before the next character has been completely shifted in. Oth-
erwise, the first byte is lost.
In SPI Slave mode, the control logic will sample the incoming signal of the SCK pin. To ensure
correct sampling of the clock signal, the minimum low and high periods should be:
Low periods: Longer than 2 CPU clock cycles.
High periods: Longer than 2 CPU clock cycles.
When the SPI is enabled, the data direction of the MOSI, MISO, SCK, and SS pins is overridden
according to Table 65. For more details on automatic port overrides, refer to “Alternate Port
Functions” on page 68.
Note: 1. See “Alternate Functions Of Port B” on page 72 for a detailed description of how to define the
direction of the user defined SPI pins.
Table 65. SPI Pin Overrides(1)
Pin Direction, Master SPI Direction, Slave SPI
MOSI User Defined Input
MISO Input User Defined
SCK User Defined Input
SS User Defined Input
MSB MASTER LSB
8-BIT SHIFT REGISTER
MSB SLAVE LSB
8-BIT SHIFT REGISTER
MISO
MOSI
SPI
CLOCK GENERATOR
SCK
SS
MISO
MOSI
SCK
SS
V
CC
SHIFT
ENABLE
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The following code examples show how to initialize the SPI as a Master and how to perform a
simple transmission. DDR_SPI in the examples must be replaced by the actual Data Direction
Register controlling the SPI pins. DD_MOSI, DD_MISO, and DD_SCK must be replaced by the
actual data direction bits for these pins. E.g., if MOSI is placed on pin PB5, replace DD_MOSI
with DDB5 and DDR_SPI with DDRB.
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Note: 1. The example code assumes that the part specific header file is included.
Assembly Code Example(1)
SPI_MasterInit:
; Set MOSI and SCK outpu?, all others input
ldi r17,(1<<DD_MOSI)|(1<<DD_SCK)
out DDR_SPI,r17
; Enable SPI, Master, se? clock rate fck/16
ldi r17,(1<<SPE)|(1<<MSTR)|(1<<SPR0)
out SPCR,r17
ret
SPI_MasterTransmit:
; Start transmission of ?ata (r16)
out SPDR,r16
Wait_Transmit:
; Wait for transmission ?omplete
sbis SPSR,SPIF
rjmp Wait_Transmit
ret
C Code Example(1)
void SPI_MasterInit(void)
{
/* Set MOSI and SCK outp?t, all others input */
DDR_SPI = (1<<DD_MOSI)|(?<<DD_SCK);
/* Enable SPI, Master, s?t clock rate fck/16 */
SPCR = (1<<SPE)|(1<<MSTR?|(1<<SPR0);
}
void SPI_MasterTransmit(char cData)
{
/* Start transmission */
SPDR = cData;
/* Wait for transmission?complete */
while(!(SPSR & (1<<?PIF)))
;
}
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The following code examples show how to initialize the SPI as a slave and how to perform a sim-
ple reception.
Note: 1. The example code assumes that the part specific header file is included.
Assembly Code Example(1)
SPI_SlaveInit:
; Set MISO output, all o?hers input
ldi r17,(1<<DD_MISO)
out DDR_SPI,r17
; Enable SPI
ldi r17,(1<<SPE)
out SPCR,r17
ret
SPI_SlaveReceive:
; Wait for reception com?lete
sbis SPSR,SPIF
rjmp SPI_SlaveReceive
; Read received data and?return
in r16,SPDR
ret
C Code Example(1)
void SPI_SlaveInit(void)
{
/* Set MISO output, all ?thers input */
DDR_SPI = (1<<DD_MISO);
/* Enable SPI */
SPCR = (1<<SPE);
}
char SPI_SlaveReceive(void)
{
/* Wait for reception co?plete */
while(!(SPSR & (1<<?PIF)))
;
/* Return data register ?/
return SPDR;
}
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SS Pin
Functionality
Slave Mode When the SPI is configured as a slave, the Slave Select (SS) pin is always input. When SS is
held low, the SPI is activated, and MISO becomes an output if configured so by the user. All
other pins are inputs. When SS is driven high, all pins are inputs except MISO which can be user
configured as an output, and the SPI is passive, which means that it will not receive incoming
data. Note that the SPI logic will be reset once the SS pin is driven high.
The SS pin is useful for packet/byte synchronization to keep the slave bit counter synchronous
with the master clock generator. When the SS pin is driven high, the SPI Slave will immediately
reset the send and receive logic, and drop any partially received data in the Shift Register.
Master Mode When the SPI is configured as a Master (MSTR in SPCR is set), the user can determine the
direction of the SS pin.
If SS is configured as an output, the pin is a general output pin which does not affect the SPI
system. Typically, the pin will be driving the SS pin of the SPI Slave.
If SS is configured as an input, it must be held high to ensure Master SPI operation. If the SS pin
is driven low by peripheral circuitry when the SPI is configured as a Master with the SS pin
defined as an input, the SPI system interprets this as another Master selecting the SPI as a
slave And starting to send data to it. To avoid bus contention, the SPI system takes the following
actions:
1. The MSTR bit in SPCR is cleared and the SPI system becomes a Slave. As a result of
the SPI becoming a Slave, the MOSI and SCK pins become inputs.
2. The SPIF Flag in SPSR is set, and if the SPI interrupt is enabled, and the I-bit in SREG is
set, the interrupt routine will be executed.
Thus, when interrupt-driven SPI transmission is used in Master mode, and there exists a possi-
bility that SS is driven low, the interrupt should always check that the MSTR bit is still set. If the
MSTR bit has been cleared by a slave select, it must be set by the user to re-enable SPI Master
mode.
SPI Control Register –
SPCR
• Bit 7 – SPIE: SPI Interrupt Enable
This bit causes the SPI interrupt to be executed if SPIF bit in the SPSR Register is set and the if
the Global Interrupt Enable bit in SREG is set.
• Bit 6 – SPE: SPI Enable
When the SPE bit is written to one, the SPI is enabled. This bit must be set to enable any SPI
operations.
• Bit 5 – DORD: Data Order
When the DORD bit is written to one, the LSB of the data word is transmitted first.
When the DORD bit is written to zero, the MSB of the data word is transmitted first.
Bit 76543210
SPIE SPE DORD MSTR CPOL CPHA SPR1 SPR0 SPCR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
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• Bit 4 – MSTR: Master/Slave Select
This bit selects Master SPI mode when written to one, and Slave SPI mode when written logic
zero. If SS is configured as an input and is driven low while MSTR is set, MSTR will be cleared,
and SPIF in SPSR will become set. The user will then have to set MSTR to re-enable SPI Mas-
ter mode.
• Bit 3 – CPOL: Clock Polarity
When this bit is written to one, SCK is high when idle. When CPOL is written to zero, SCK is low
when idle. Refer to Figure 73 and Figure 74 for an example. The CPOL functionality is summa-
rized below:
• Bit 2 – CPHA: Clock Phase
The settings of the Clock Phase bit (CPHA) determine if data is sampled on the leading (first) or
trailing (last) edge of SCK. Refer to Figure 73 and Figure 74 for an example. The CPHA func-
tionality is summarized below:
• Bits 1, 0 – SPR1, SPR0: SPI Clock Rate Select 1 and 0
These two bits control the SCK rate of the device configured as a Master. SPR1 and SPR0 have
no effect on the Slave. The relationship between SCK and the Oscillator Clock frequency fosc is
shown in the following table:
Table 66. CPOL Functionality
CPOL Leading Edge Trailing Edge
0 Rising Falling
1 Falling Rising
Table 67. CPHA Functionality
CPHA Leading Edge Trailing Edge
0 Sample Setup
1 Setup Sample
Table 68. Relationship Between SCK and the Oscillator Frequency
SPI2X SPR1 SPR0 SCK Frequency
000
fosc/4
001
fosc/16
010
fosc/64
011
fosc/128
100
fosc/2
101
fosc/8
110
fosc/32
111
fosc/64
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SPI Status Register –
SPSR
• Bit 7 – SPIF: SPI Interrupt Flag
When a serial transfer is complete, the SPIF Flag is set. An interrupt is generated if SPIE in
SPCR is set and global interrupts are enabled. If SS is an input and is driven low when the SPI is
in master mode, this will also set the SPIF Flag. SPIF is cleared by hardware when executing the
corresponding interrupt handling vector. Alternatively, the SPIF bit is cleared by first reading the
SPI Status Register with SPIF set, then accessing the SPI Data Register (SPDR).
• Bit 6 – WCOL: Write COLlision Flag
The WCOL bit is set if the SPI Data Register (SPDR) is written during a data transfer. The
WCOL bit (and the SPIF bit) are cleared by first reading the SPI Status Register with WCOL set,
and then accessing the SPI Data Register.
• Bit 5..1 – Res: Reserved Bits
These bits are reserved bits in the ATmega162 and will always read as zero.
• Bit 0 – SPI2X: Double SPI Speed Bit
When this bit is written logic one the SPI speed (SCK Frequency) will be doubled when the SPI
is in Master mode (see Table 68). This means that the minimum SCK period will be two CPU
clock periods. When the SPI is configured as Slave, the SPI is only guaranteed to work at fosc/4
or lower.
The SPI interface on the ATmega162 is also used for program memory and EEPROM down-
loading or uploading. See page 245 for SPI serial programming and verification.
SPI Data Register –
SPDR
The SPI Data Register is a read/write register used for data transfer between the Register File
and the SPI Shift Register. Writing to the register initiates data transmission. Reading the regis-
ter causes the Shift Register receive buffer to be read.
Bit 76543210
SPIFWCOL–––––SPI2XSPSR
Read/WriteRRRRRRRR/W
Initial Value00000000
Bit 76543210
MSB LSB SPDR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value X X X X X X X X Undefined
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Data Modes There are four combinations of SCK phase and polarity with respect to serial data, which are
determined by control bits CPHA and CPOL. The SPI data transfer formats are shown in Figure
73 and Figure 74. Data bits are shifted out and latched in on opposite edges of the SCK signal,
ensuring sufficient time for data signals to stabilize. This is clearly seen by summarizing Table
66 and Table 67, as done below:
Figure 73. SPI Transfer Format with CPHA = 0
Figure 74. SPI Transfer Format with CPHA = 1
Table 69. CPOL and CPHA Functionality
Leading Edge Trailing Edge SPI Mode
CPOL=0, CPHA=0 Sample (Rising) Setup (Falling) 0
CPOL=0, CPHA=1 Setup (Rising) Sample (Falling) 1
CPOL=1, CPHA=0 Sample (Falling) Setup (Rising) 2
CPOL=1, CPHA=1 Setup (Falling) Sample (Rising) 3
Bit 1
Bit 6
LSB
MSB
SCK (CPOL = 0)
mode 0
SAMPLE I
MOSI/MISO
CHANGE 0
MOSI PIN
CHANGE 0
MISO PIN
SCK (CPOL = 1)
mode 2
SS
MSB
LSB
Bit 6
Bit 1
Bit 5
Bit 2
Bit 4
Bit 3
Bit 3
Bit 4
Bit 2
Bit 5
MSB first (DORD = 0)
LSB first (DORD = 1)
SCK (CPOL = 0)
mode 1
SAMPLE I
MOSI/MISO
CHANGE 0
MOSI PIN
CHANGE 0
MISO PIN
SCK (CPOL = 1)
mode 3
SS
MSB
LSB
Bit 6
Bit 1
Bit 5
Bit 2
Bit 4
Bit 3
Bit 3
Bit 4
Bit 2
Bit 5
Bit 1
Bit 6
LSB
MSB
MSB first (DORD = 0)
LSB first (DORD = 1)
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USART The Universal Synchronous and Asynchronous serial Receiver and Transmitter (USART) is a
highly flexible serial communication device. The main features are:
•Full Duplex Operation (Independent Serial Receive and Transmit Registers)
•Asynchronous or Synchronous Operation
•Master or Slave Clocked Synchronous Operation
•High Resolution Baud Rate Generator
•Supports Serial Frames with 5, 6, 7, 8, or 9 Data Bits and 1 or 2 Stop Bits
•Odd or Even Parity Generation and Parity Check Supported by Hardware
•Data OverRun Detection
•Framing Error Detection
•Noise Filtering Includes False Start Bit Detection and Digital Low Pass Filter
•Three Separate Interrupts on TX Complete, TX Data Register Empty and RX Complete
•Multi-processor Communication Mode
•Double Speed Asynchronous Communication Mode
Dual USART The ATmega162 has two USARTs, USART0 and USART1. The functionality for both USARTs is
described below.
USART0 and USART1 have different I/O Registers as shown in “Register Summary” on page
304. Note that in ATmega161 compatibility mode, the double buffering of the USART Receive
Register is disabled. For details, see “AVR USART vs. AVR UART – Compatibility” on page 168.
Note also that the shared UBRRHI Register in ATmega161 has been split into two separate reg-
isters, UBRR0H and UBRR1H, in ATmega162.
A simplified block diagram of the USART Transmitter is shown in Figure 75. CPU accessible I/O
Registers and I/O pins are shown in bold.
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Figure 75. USART Block Diagram(1)
Note: 1. Refer to Figure 1 on page 2, Table 34 on page 74, Table 39 on page 80, and Table 40 on page
80 for USART pin placement.
The dashed boxes in the block diagram separate the three main parts of the USART (listed from
the top): Clock Generator, Transmitter and Receiver. Control registers are shared by all units.
The Clock Generation logic consists of synchronization logic for external clock input used by
synchronous slave operation, and the baud rate generator. The XCK (Transfer Clock) pin is only
used by synchronous transfer mode. The Transmitter consists of a single write buffer, a serial
Shift Register, parity generator and control logic for handling different serial frame formats. The
write buffer allows a continuous transfer of data without any delay between frames. The
Receiver is the most complex part of the USART module due to its clock and data recovery
units. The recovery units are used for asynchronous data reception. In addition to the recovery
units, the Receiver includes a Parity Checker, Control logic, a Shift Register and a two level
receive buffer (UDR). The receiver supports the same frame formats as the Transmitter, and can
detect Frame Error, Data OverRun and Parity Errors.
PARITY
GENERATOR
UBRR[H:L]
UDR (Transmit)
UCSRA UCSRB UCSRC
BAUD RATE GENERATOR
TRANSMIT SHIFT REGISTER
RECEIVE SHIFT REGISTER RxD
TxD
PIN
CONTROL
UDR (Receive)
PIN
CONTROL
XCK
DATA
RECOVERY
CLOCK
RECOVERY
PIN
CONTROL
TX
CONTROL
RX
CONTROL
PARITY
CHECKER
DATABUS
OSC
SYNC LOGIC
Clock Generator
Transmitter
Receiver
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AVR USART vs. AVR
UART – Compatibility
The USART is fully compatible with the AVR UART regarding:
• Bit locations inside all USART Registers
• Baud Rate Generation
• Transmitter Operation
• Transmit Buffer Functionality
• Receiver Operation
However, the receive buffering has two improvements that will affect the compatibility in some
special cases:
• A second Buffer Register has been added. The two buffer registers operate as a circular
FIFO buffer. Therefore the UDR must only be read once for each incoming data! More
important is the fact that the Error Flags (FE and DOR) and the ninth data bit (RXB8) are
buffered with the data in the receive buffer. Therefore the status bits must always be read
before the UDR Register is read. Otherwise the error status will be lost since the buffer state
is lost.
• The Receiver Shift Register can now act as a third buffer level. This is done by allowing the
received data to remain in the serial Shift Register (see Figure 75) if the Buffer Registers are
full, until a new start bit is detected. The USART is therefore more resistant to Data OverRun
(DOR) error conditions.
The following control bits have changed name, but have same functionality and register location:
• CHR9 is changed to UCSZ2.
• OR is changed to DOR.
Clock Generation The Clock Generation logic generates the base clock for the Transmitter and Receiver. The
USART supports four modes of clock operation: Normal asynchronous, Double Speed asyn-
chronous, Master synchronous and Slave synchronous mode. The UMSEL bit in USART
Control and Status Register C (UCSRC) selects between asynchronous and synchronous oper-
ation. Double Speed (asynchronous mode only) is controlled by the U2X found in the UCSRA
Register. When using synchronous mode (UMSEL = 1), the Data Direction Register for the XCK
pin (DDR_XCK) controls whether the clock source is internal (Master mode) or external (Slave
mode). The XCK pin is only active when using synchronous mode.
Figure 76 shows a block diagram of the clock generation logic.
Figure 76. Clock Generation Logic, Block Diagram
Signal description:
Prescaling
Down-Counter / 2
UBRR
/ 4 / 2
fosc
UBRR+1
Sync
Register
OSC
XCK
Pin
txclk
U2X
UMSEL
DDR_XCK
0
1
0
1
xcki
xcko
DDR_XCK rxclk
0
1
1
0
Edge
Detector
UCPOL
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txclk Transmitter clock. (Internal Signal)
rxclk Receiver base clock. (Internal Signal)
xcki Input from XCK pin (internal Signal). Used for synchronous slave operation.
xcko Clock output to XCK pin (Internal Signal). Used for synchronous master
operation.
fosc XTAL pin frequency (System Clock).
Internal Clock
Generation – The
Baud Rate Generator
Internal clock generation is used for the asynchronous and the synchronous master modes of
operation. The description in this section refers to Figure 76.
The USART Baud Rate Register (UBRR) and the down-counter connected to it function as a
programmable prescaler or baud rate generator. The down-counter, running at system clock
(fosc), is loaded with the UBRR value each time the counter has counted down to zero or when
the UBRRL Register is written. A clock is generated each time the counter reaches zero. This
clock is the baud rate generator clock output (= fosc/(UBRR+1)). The Transmitter divides the
baud rate generator clock output by 2, 8 or 16 depending on mode. The baud rate generator out-
put is used directly by the receiver’s clock and data recovery units. However, the recovery units
use a state machine that uses 2, 8 or 16 states depending on mode set by the state of the
UMSEL, U2X and DDR_XCK bits.
Table 70 contains equations for calculating the baud rate (in bits per second) and for calculating
the UBRR value for each mode of operation using an internally generated clock source.
Note: 1. The baud rate is defined to be the transfer rate in bit per second (bps).
BAUD Baud rate (in bits per second, bps)
fOSC System Oscillator clock frequency
UBRR Contents of the UBRRH and UBRRL Registers, (0 - 4095)
Some examples of UBRR values for some system clock frequencies are found in Table 78 (see
page 191).
Table 70. Equations for Calculating Baud Rate Register Setting
Operating Mode
Equation for Calculating
Baud Rate(1)
Equation for Calculating
UBRR Value
Asynchronous Normal Mode
(U2X = 0)
Asynchronous Double Speed
Mode (U2X = 1)
Synchronous Master Mode
BAUD fOSC
16 UBRR 1+()
---------------------------------------=
UBRR fOSC
16BAUD
------------------------1–=
BAUD fOSC
8UBRR 1+()
-----------------------------------=
UBRR fOSC
8BAUD
-------------------- 1–=
BAUD fOSC
2UBRR 1+()
-----------------------------------=
UBRR fOSC
2BAUD
-------------------- 1–=
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Double Speed
Operation (U2X)
The transfer rate can be doubled by setting the U2X bit in UCSRA. Setting this bit only has effect
for the asynchronous operation. Set this bit to zero when using synchronous operation.
Setting this bit will reduce the divisor of the baud rate divider from 16 to 8, effectively doubling
the transfer rate for asynchronous communication. Note however that the Receiver will in this
case only use half the number of samples (reduced from 16 to 8) for data sampling and clock
recovery, and therefore a more accurate baud rate setting and system clock are required when
this mode is used. For the Transmitter, there are no downsides.
External Clock External clocking is used by the synchronous slave modes of operation. The description in this
section refers to Figure 76 for details.
External clock input from the XCK pin is sampled by a synchronization register to minimize the
chance of meta-stability. The output from the synchronization register must then pass through
an edge detector before it can be used by the Transmitter and Receiver. This process intro-
duces a two CPU clock period delay and therefore the maximum external XCK clock frequency
is limited by the following equation:
Note that fosc depends on the stability of the system clock source. It is therefore recommended to
add some margin to avoid possible loss of data due to frequency variations.
Synchronous Clock
Operation
When synchronous mode is used (UMSEL = 1), the XCK pin will be used as either clock input
(Slave) or clock output (Master). The dependency between the clock edges and data sampling
or data change is the same. The basic principle is that data input (on RxD) is sampled at the
opposite XCK clock edge of the edge the data output (TxD) is changed.
Figure 77. Synchronous Mode XCK Timing.
The UCPOL bit UCRSC selects which XCK clock edge is used for data sampling and which is
used for data change. As Figure 77 shows, when UCPOL is zero the data will be changed at ris-
ing XCK edge and sampled at falling XCK edge. If UCPOL is set, the data will be changed at
falling XCK edge and sampled at rising XCK edge.
fXCK
fOSC
4
-----------<
RxD / TxD
XCK
RxD / TxD
XCK
UCPOL = 0
UCPOL = 1
Sample
Sample
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Frame Formats A serial frame is defined to be one character of data bits with synchronization bits (start and stop
bits), and optionally a parity bit for error checking. The USART accepts all 30 combinations of
the following as valid frame formats:
• 1 start bit
• 5, 6, 7, 8, or 9 data bits
• no, even or odd parity bit
• 1 or 2 stop bits
A frame starts with the start bit followed by the least significant data bit. Then the next data bits,
up to a total of nine, are succeeding, ending with the most significant bit. If enabled, the parity bit
is inserted after the data bits, before the stop bits. When a complete frame is transmitted, it can
be directly followed by a new frame, or the communication line can be set to an idle (high) state.
Figure 78 illustrates the possible combinations of the frame formats. Bits inside brackets are
optional.
Figure 78. Frame Formats
St Start bit, always low.
(n) Data bits (0 to 8).
PParity bit. Can be odd or even.
Sp Stop bit, always high.
IDLE No transfers on the communication line (RxD or TxD). An IDLE line must be
high.
The frame format used by the USART is set by the UCSZ2:0, UPM1:0 and USBS bits in UCSRB
and UCSRC. The Receiver and Transmitter use the same setting. Note that changing the setting
of any of these bits will corrupt all ongoing communication for both the Receiver and Transmitter.
The USART Character SiZe (UCSZ2:0) bits select the number of data bits in the frame. The
USART Parity mode (UPM1:0) bits enable and set the type of parity bit. The selection between
one or two stop bits is done by the USART Stop Bit Select (USBS) bit. The receiver ignores the
second stop bit. An FE (Frame Error) will therefore only be detected in the cases where the first
stop bit is zero.
Parity Bit Calculation The parity bit is calculated by doing an exclusive-or of all the data bits. If odd parity is used, the
result of the exclusive or is inverted. The relation between the parity bit and data bits is as
follows::
Peven Parity bit using even parity
Podd Parity bit using odd parity
dnData bit n of the character
If used, the parity bit is located between the last data bit and first stop bit of a serial frame.
10 2 3 4 [5] [6] [7] [8] [P]St Sp1 [Sp2] (St / IDLE)(IDLE)
FRAME
Peven dn1–…d3d2d1d00
Podd
⊕⊕⊕⊕⊕⊕
dn1–…d3d2d1d01⊕⊕⊕⊕⊕⊕
=
=
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USART
Initialization
The USART has to be initialized before any communication can take place. The initialization pro-
cess normally consists of setting the baud rate, setting frame format and enabling the
Transmitter or the Receiver depending on the usage. For interrupt driven USART operation, the
Global Interrupt Flag should be cleared (and interrupts globally disabled) when doing the
initialization.
Before doing a re-initialization with changed baud rate or frame format, be sure that there are no
ongoing transmissions during the period the registers are changed. The TXC Flag can be used
to check that the Transmitter has completed all transfers, and the RXC Flag can be used to
check that there are no unread data in the receive buffer. Note that the TXC Flag must be
cleared before each transmission (before UDR is written) if it is used for this purpose.
The following simple USART initialization code examples show one assembly and one C func-
tion that are equal in functionality. The examples assume asynchronous operation using polling
(no interrupts enabled) and a fixed frame format. The baud rate is given as a function parameter.
For the assembly code, the baud rate parameter is assumed to be stored in the r17:r16 Regis-
ters. When the function writes to the UCSRC Register, the URSEL bit (MSB) must be set due to
the sharing of I/O location by UBRRH and UCSRC.
Note: 1. See “About Code Examples” on page 8.
Assembly Code Example(1)
USART_Init:
; Set baud rate
out UBRRH, r17
out UBRRL, r16
; Enable receiver a?d transmitter
ldi r16, (1<<RXEN)|(1<<TXEN)
out UCSRB,r16
; Set frame format:?8data, 2stop bit
ldi r16, (1<<URSEL)|(1<<USBS)|(3<<UCSZ0)
out UCSRC,r16
ret
C Code Example(1)
#define FOSC 1843200// Clock Speed
#define BAUD 9600
#define MYUBRR FOSC/16/BAUD-1
void main( void )
{
...
USART_Init ( MYUBRR );
...
}
void USART_Init( unsigned int ubrr )
{
/* Set baud rate */
UBRRH = (unsigned c?ar)(ubrr>>8);
UBRRL = (unsigned c?ar)ubrr;
/* Enable receiver ?nd transmitter */
UCSRB = (1<<RXEN)|(1<<TX?N);
/* Set frame format? 8data, 2stop bit */
UCSRC = (1<<URSEL)|(1<<U?BS)|(3<<UCSZ0);
}
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More advanced initialization routines can be made that include frame format as parameters, dis-
able interrupts and so on. However, many applications use a fixed setting of the Baud and
Control Registers, and for these types of applications the initialization code can be placed
directly in the main routine, or be combined with initialization code for other I/O modules.
Data Transmission
– The USART
Transmitter
The USART Transmitter is enabled by setting the Transmit Enable (TXEN) bit in the UCSRB
Register. When the Transmitter is enabled, the normal port operation of the TxD pin is overrid-
den by the USART and given the function as the transmitter’s serial output. The baud rate, mode
of operation and frame format must be set up once before doing any transmissions. If synchro-
nous operation is used, the clock on the XCK pin will be overridden and used as transmission
clock.
Sending Frames with
5 to 8 Data Bit
A data transmission is initiated by loading the transmit buffer with the data to be transmitted. The
CPU can load the transmit buffer by writing to the UDR I/O location. The buffered data in the
transmit buffer will be moved to the Shift Register when the Shift Register is ready to send a new
frame. The Shift Register is loaded with new data if it is in idle state (no ongoing transmission) or
immediately after the last stop bit of the previous frame is transmitted. When the Shift Register is
loaded with new data, it will transfer one complete frame at the rate given by the Baud Register,
U2X bit or by XCK depending on mode of operation.
The following code examples show a simple USART transmit function based on polling of the
Data Register Empty (UDRE) Flag. When using frames with less than eight bits, the most signif-
icant bits written to the UDR are ignored. The USART has to be initialized before the function
can be used. For the assembly code, the data to be sent is assumed to be stored in Register
R16
Note: 1. The example code assumes that the part specific header file is included.
The function simply waits for the transmit buffer to be empty by checking the UDRE Flag, before
loading it with new data to be transmitted. If the Data Register Empty interrupt is utilized, the
interrupt routine writes the data into the buffer.
Assembly Code Example(1)
USART_Transmit:
; Wait for empty tr?nsmit buffer
sbis UCSRA,UDRE
rjmp USART_Transmit
; Put data (r16) in?o buffer, sends the data
out UDR,r16
ret
C Code Example(1)
void USART_Transmit( unsigned char data )
{
/* Wait for empty t?ansmit buffer */
while ( !( UCSRA & ?1<<UDRE)) )
;
/* Put data into bu?fer, sends the data */
UDR = data;
}
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Sending Frames with
9 Data Bit
If 9-bit characters are used (UCSZ = 7), the ninth bit must be written to the TXB8 bit in UCSRB
before the low byte of the character is written to UDR. The following code examples show a
transmit function that handles 9-bit characters. For the assembly code, the data to be sent is
assumed to be stored in Registers R17:R16.
Note: 1. These transmit functions are written to be general functions. They can be optimized if the con-
tents of the UCSRB is static. For example, only the TXB8 bit of the UCSRB Register is used
after initialization.
The ninth bit can be used for indicating an address frame when using multi processor communi-
cation mode or for other protocol handling as for example synchronization.
Transmitter Flags and
Interrupts
The USART Transmitter has two flags that indicate its state: USART Data Register Empty
(UDRE) and Transmit Complete (TXC). Both flags can be used for generating interrupts.
The Data Register Empty (UDRE) Flag indicates whether the transmit buffer is ready to receive
new data. This bit is set when the transmit buffer is empty, and cleared when the transmit buffer
contains data to be transmitted that has not yet been moved into the Shift Register. For compat-
ibility with future devices, always write this bit to zero when writing the UCSRA Register.
When the Data Register Empty Interrupt Enable (UDRIE) bit in UCSRB is written to one, the
USART Data Register Empty Interrupt will be executed as long as UDRE is set (provided that
global interrupts are enabled). UDRE is cleared by writing UDR. When interrupt-driven data
transmission is used, the Data Register Empty Interrupt routine must either write new data to
UDR in order to clear UDRE or disable the Data Register Empty Interrupt, otherwise a new inter-
rupt will occur once the interrupt routine terminates.
Assembly Code Example(1)
USART_Transmit:
; Wait for empty tr?nsmit buffer
sbis UCSRA,UDRE
rjmp USART_Transmit
; Copy 9th bit from?r17 to TXB8
cbi UCSRB,TXB8
sbrc r17,0
sbi UCSRB,TXB8
; Put LSB data (r16? into buffer, sends the data
out UDR,r16
ret
C Code Example(1)
void USART_Transmit( unsigned int data )
{
/* Wait for empty t?ansmit buffer */
while ( !( UCSRA & ?1<<UDRE)) )
;
/* Copy 9th bit to ?XB8 */
UCSRB &= ~(1<<TXB8);
if ( data & 0x0100 )
UCSRB |= (1<<TXB8);
/* Put data into bu?fer, sends the data */
UDR = data;
}
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The Transmit Complete (TXC) Flag bit is set one when the entire frame in the Transmit Shift
Register has been shifted out and there are no new data currently present in the transmit buffer.
The TXC Flag bit is automatically cleared when a transmit complete interrupt is executed, or it
can be cleared by writing a one to its bit location. The TXC Flag is useful in half-duplex commu-
nication interfaces (like the RS-485 standard), where a transmitting application must enter
Receive mode and free the communication bus immediately after completing the transmission.
When the Transmit Compete Interrupt Enable (TXCIE) bit in UCSRB is set, the USART Transmit
Complete Interrupt will be executed when the TXC Flag becomes set (provided that global inter-
rupts are enabled). When the transmit complete interrupt is used, the interrupt handling routine
does not have to clear the TXC Flag, this is done automatically when the interrupt is executed.
Parity Generator The Parity Generator calculates the parity bit for the serial frame data. When parity bit is enabled
(UPM1 = 1), the transmitter control logic inserts the parity bit between the last data bit and the
first stop bit of the frame that is sent.
Disabling the
Transmitter
The disabling of the Transmitter (setting the TXEN to zero) will not become effective until ongo-
ing and pending transmissions are completed, i.e., when the Transmit Shift Register and
Transmit Buffer Register do not contain data to be transmitted. When disabled, the Transmitter
will no longer override the TxD pin.
Data Reception –
The USART
Receiver
The USART Receiver is enabled by writing the Receive Enable (RXEN) bit in the UCSRB Regis-
ter to one. When the receiver is enabled, the normal pin operation of the RxD pin is overridden
by the USART and given the function as the receiver’s serial input. The baud rate, mode of oper-
ation and frame format must be set up once before any serial reception can be done. If
synchronous operation is used, the clock on the XCK pin will be used as transfer clock.
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Receiving Frames with
5 to 8 Data Bits
The Receiver starts data reception when it detects a valid start bit. Each bit that follows the start
bit will be sampled at the baud rate or XCK clock, and shifted into the Receive Shift Register until
the first stop bit of a frame is received. A second stop bit will be ignored by the Receiver. When
the first stop bit is received, i.e., a complete serial frame is present in the Receive Shift Register,
the contents of the Shift Register will be moved into the receive buffer. The receive buffer can
then be read by reading the UDR I/O location.
The following code example shows a simple USART receive function based on polling of the
Receive Complete (RXC) Flag. When using frames with less than eight bits the most significant
bits of the data read from the UDR will be masked to zero. The USART has to be initialized
before the function can be used.
Note: 1. The example code assumes that the part specific header file is included.
The function simply waits for data to be present in the receive buffer by checking the RXC Flag,
before reading the buffer and returning the value.
Assembly Code Example(1)
USART_Receive:
; Wait for data to ?e received
sbis UCSRA, RXC
rjmp USART_Receive
; Get and return re?eived data from buffer
in r16, UDR
ret
C Code Example(1)
unsigned char USART_Receive( void )
{
/* Wait for data to?be received */
while ( !(UCSRA & (?<<RXC)) )
;
/* Get and return r?ceived data from buffer */
return UDR;
}
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Receiving Frames with
9 Data Bits
If 9-bit characters are used (UCSZ=7) the ninth bit must be read from the RXB8 bit in UCSRB
before reading the low bits from the UDR. This rule applies to the FE, DOR and UPE Status
Flags as well. Read status from UCSRA, then data from UDR. Reading the UDR I/O location will
change the state of the receive buffer FIFO and consequently the TXB8, FE, DOR and UPE bits,
which all are stored in the FIFO, will change.
The following code example shows a simple USART receive function that handles both nine bit
characters and the status bits.
Note: 1. The example code assumes that the part specific header file is included.
Assembly Code Example(1)
USART_Receive:
; Wait for data to ?e received
sbis UCSRA, RXC
rjmp USART_Receive
; Get status and 9t? bit, then data from buffer
in r18, UCSRA
in r17, UCSRB
in r16, UDR
; If error, return ?1
andi r18,(1<<FE)|(1<<DOR)|(1<<UPE)
breq USART_ReceiveNoError
ldi r17, HIGH(-1)
ldi r16, LOW(-1)
USART_ReceiveNoError:
; Filter the 9th bi?, then return
lsr r17
andi r17, 0x01
ret
C Code Example(1)
unsigned int USART_Receive( void )
{
unsigned char statu?, resh, resl;
/* Wait for data to?be received */
while ( !(UCSRA & (?<<RXC)) )
;
/* Get status and 9?h bit, then data */
/* from buffer */
status = UCSRA;
resh = UCSRB;
resl = UDR;
/* If error, return?-1 */
if ( status & (1<<F?)|(1<<DOR)|(1<<UPE) )
return -1;
/* Filter the 9th b?t, then return */
resh = (resh >> 1) & 0x0?;
return ((resh << 8)?| resl);
}
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The receive function example reads all the I/O Registers into the Register File before any com-
putation is done. This gives an optimal receive buffer utilization since the buffer location read will
be free to accept new data as early as possible.
Receive Compete Flag
and Interrupt
The USART Receiver has one flag that indicates the receiver state.
The Receive Complete (RXC) Flag indicates if there are unread data present in the receive buf-
fer. This flag is one when unread data exist in the receive buffer, and zero when the receive
buffer is empty (i.e., does not contain any unread data). If the Receiver is disabled (RXEN = 0),
the receive buffer will be flushed and consequently the RXC bit will become zero.
When the Receive Complete Interrupt Enable (RXCIE) in UCSRB is set, the USART Receive
Complete Interrupt will be executed as long as the RXC Flag is set (provided that global inter-
rupts are enabled). When interrupt-driven data reception is used, the receive complete routine
must read the received data from UDR in order to clear the RXC Flag, otherwise a new interrupt
will occur once the interrupt routine terminates.
Receiver Error Flags The USART Receiver has three Error Flags: Frame Error (FE), Data OverRun (DOR) and Parity
Error (UPE). All can be accessed by reading UCSRA. Common for the Error Flags is that they
are located in the receive buffer together with the frame for which they indicate the error status.
Due to the buffering of the Error Flags, the UCSRA must be read before the receive buffer
(UDR), since reading the UDR I/O location changes the buffer read location. Another equality for
the Error Flags is that they can not be altered by software doing a write to the flag location. How-
ever, all flags must be set to zero when the UCSRA is written for upward compatibility of future
USART implementations. None of the Error Flags can generate interrupts.
The Frame Error (FE) Flag indicates the state of the first stop bit of the next readable frame
stored in the receive buffer. The FE Flag is zero when the stop bit was correctly read (as one),
and the FE Flag will be one when the stop bit was incorrect (zero). This flag can be used for
detecting out-of-sync conditions, detecting break conditions and protocol handling. The FE Flag
is not affected by the setting of the USBS bit in UCSRC since the receiver ignores all, except for
the first, stop bits. For compatibility with future devices, always set this bit to zero when writing to
UCSRA.
The Data OverRun (DOR) Flag indicates data loss due to a receiver buffer full condition. A Data
OverRun occurs when the receive buffer is full (two characters), it is a new character waiting in
the Receive Shift Register, and a new start bit is detected. If the DOR Flag is set there was one
or more serial frame lost between the frame last read from UDR, and the next frame read from
UDR. For compatibility with future devices, always write this bit to zero when writing to UCSRA.
The DOR Flag is cleared when the frame received was successfully moved from the Shift Regis-
ter to the receive buffer.
The Parity Error (UPE) Flag indicates that the next frame in the receive buffer had a Parity Error
when received. If parity check is not enabled the UPE bit will always be read zero. For compati-
bility with future devices, always set this bit to zero when writing to UCSRA. For more details see
“Parity Bit Calculation” on page 171 and “Parity Checker” on page 179.
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Parity Checker The Parity Checker is active when the high USART Parity mode (UPM1) bit is set. Type of parity
check to be performed (odd or even) is selected by the UPM0 bit. When enabled, the Parity
Checker calculates the parity of the data bits in incoming frames and compares the result with
the parity bit from the serial frame. The result of the check is stored in the receive buffer together
with the received data and stop bits. The Parity Error (UPE) Flag can then be read by software to
check if the frame had a Parity Error.
The UPE bit is set if the next character that can be read from the receive buffer had a parity error
when received and the parity checking was enabled at that point (UPM1 = 1). This bit is valid
until the receive buffer (UDR) is read.
Disabling the Receiver In contrast to the Transmitter, disabling of the Receiver will be immediate. Data from ongoing
receptions will therefore be lost. When disabled (i.e., the RXEN is set to zero) the receiver will no
longer override the normal function of the RxD port pin. The receiver buffer FIFO will be flushed
when the receiver is disabled. Remaining data in the buffer will be lost
Flushing the Receive
Buffer
The receiver buffer FIFO will be flushed when the Receiver is disabled, i.e., the buffer will be
emptied of its contents. Unread data will be lost. If the buffer has to be flushed during normal
operation, due to for instance an error condition, read the UDR I/O location until the RXC Flag is
cleared. The following code example shows how to flush the receive buffer.
Note: 1. The example code assumes that the part specific header file is included.
Asynchronous
Data Reception
The USART includes a clock recovery and a data recovery unit for handling asynchronous data
reception. The clock recovery logic is used for synchronizing the internally generated baud rate
clock to the incoming asynchronous serial frames at the RxD pin. The data recovery logic sam-
ples and low pass filters each incoming bit, thereby improving the noise immunity of the receiver.
The asynchronous reception operational range depends on the accuracy of the internal baud
rate clock, the rate of the incoming frames, and the frame size in number of bits.
Asynchronous Clock
Recovery
The clock recovery logic synchronizes internal clock to the incoming serial frames. Figure 79
illustrates the sampling process of the start bit of an incoming frame. The sample rate is 16 times
the baud rate for Normal mode, and 8 times the baud rate for Double Speed mode. The horizon-
tal arrows illustrate the synchronization variation due to the sampling process. Note the larger
time variation when using the double speed mode (U2X = 1) of operation. Samples denoted zero
are samples done when the RxD line is idle (i.e., no communication activity).
Assembly Code Example(1)
USART_Flush:
sbis UCSRA, RXC
ret
in r16, UDR
rjmp USART_Flush
C Code Example(1)
void USART_Flush( void )
{
unsigned char dummy?
while ( UCSRA & (1<?RXC) ) dummy = UDR;
}
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Figure 79. Start Bit Sampling
When the clock recovery logic detects a high (idle) to low (start) transition on the RxD line, the
start bit detection sequence is initiated. Let sample 1 denote the first zero-sample as shown in
the figure. The clock recovery logic then uses samples 8, 9 and 10 for Normal mode, and sam-
ples 4, 5 and 6 for Double Speed mode (indicated with sample numbers inside boxes on the
figure), to decide if a valid start bit is received. If two or more of these three samples have logical
high levels (the majority wins), the start bit is rejected as a noise spike and the receiver starts
looking for the next high to low-transition. If however, a valid start bit is detected, the clock recov-
ery logic is synchronized and the data recovery can begin. The synchronization process is
repeated for each start bit.
Asynchronous Data
Recovery
When the receiver clock is synchronized to the start bit, the data recovery can begin. The data
recovery unit uses a state machine that has 16 states for each bit in Normal mode and 8 states
for each bit in Double Speed mode. Figure 80 shows the sampling of the data bits and the parity
bit. Each of the samples is given a number that is equal to the state of the recovery unit.
Figure 80. Sampling of Data and Parity Bit
The decision of the logic level of the received bit is taken by doing a majority voting of the logic
value to the three samples in the center of the received bit. The center samples are emphasized
on the figure by having the sample number inside boxes. The majority voting process is done as
follows: If two or all three samples have high levels, the received bit is registered to be a logic 1.
If two or all three samples have low levels, the received bit is registered to be a logic 0. This
majority voting process acts as a low pass filter for the incoming signal on the RxD pin. The
recovery process is then repeated until a complete frame is received. Including the first stop bit.
Note that the receiver only uses the first stop bit of a frame.
Figure 81 shows the sampling of the stop bit and the earliest possible beginning of the start bit of
the next frame.
12345678 9 10 11 12 13 14 15 16 12
STARTIDLE
00
BIT 0
3
1234 5 678120
RxD
Sample
(U2X = 0)
Sample
(U2X = 1)
12345678 9 10 11 12 13 14 15 16 1
BIT n
1234 5 6781
RxD
Sample
(U2X = 0)
Sample
(U2X = 1)
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Figure 81. Stop Bit Sampling and Next Start Bit Sampling
The same majority voting is done to the stop bit as done for the other bits in the frame. If the stop
bit is registered to have a logic 0 value, the Frame Error (FE) Flag will be set.
A new high to low transition indicating the start bit of a new frame can come right after the last of
the bits used for majority voting. For Normal Speed mode, the first low level sample can be at
point marked (A) in Figure 81. For Double Speed mode the first low level must be delayed to (B).
(C) marks a stop bit of full length. The early start bit detection influences the operational range of
the receiver.
Asynchronous
Operational Range
The operational range of the receiver is dependent on the mismatch between the received bit
rate and the internally generated baud rate. If the Transmitter is sending frames at too fast or too
slow bit rates, or the internally generated baud rate of the receiver does not have a similar (see
Table 71) base frequency, the receiver will not be able to synchronize the frames to the start bit.
The following equations can be used to calculate the ratio of the incoming data rate and internal
receiver baud rate.
DSum of character size and parity size (D = 5 to 10 bit)
SSamples per bit. S = 16 for Normal Speed mode and S = 8 for Double Speed
mode.
SFFirst sample number used for majority voting. SF = 8 for Normal Speed and
SF = 4 for Double Speed mode.
SMMiddle sample number used for majority voting. SM = 9 for Normal Speed and
SM = 5 for Double Speed mode.
Rslow is the ratio of the slowest incoming data rate that can be accepted in relation to the
receiver baud rate. Rfast is the ratio of the fastest incoming data rate that can be
accepted in relation to the receiver baud rate.
Table 71 and Table 72 list the maximum receiver baud rate error that can be tolerated. Note that
normal speed mode has higher toleration of baud rate variations.
12345678 9 10 0/1 0/1 0/1
STOP 1
1234 5 6 0/1
RxD
Sample
(U2X = 0)
Sample
(U2X = 1)
(A) (B) (C)
Rslow
D1+()S
S1–DS⋅SF
++
-------------------------------------------=
Rfast
D2+()S
D1+()SS
M
+
-----------------------------------=
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The recommendations of the maximum receiver baud rate error was made under the assump-
tion that the Receiver and Transmitter equally divides the maximum total error.
There are two possible sources for the receivers baud rate error. The receiver’s system clock
(XTAL) will always have some minor instability over the supply voltage range and the tempera-
ture range. When using a crystal to generate the system clock, this is rarely a problem, but for a
resonator the system clock may differ more than 2% depending of the resonators tolerance. The
second source for the error is more controllable. The baud rate generator can not always do an
exact division of the system frequency to get the baud rate wanted. In this case an UBRR value
that gives an acceptable low error can be used if possible.
Multi-processor
Communication
Mode
Setting the Multi-processor Communication mode (MPCM) bit in UCSRA enables a filtering
function of incoming frames received by the USART Receiver. Frames that do not contain
address information will be ignored and not put into the receive buffer. This effectively reduces
the number of incoming frames that has to be handled by the CPU, in a system with multiple
MCUs that communicate via the same serial bus. The Transmitter is unaffected by the MPCM
setting, but has to be used differently when it is a part of a system utilizing the Multi-processor
Communication mode.
If the receiver is set up to receive frames that contain 5 to 8 data bits, then the first stop bit indi-
cates if the frame contains data or address information. If the receiver is set up for frames with
nine data bits, then the ninth bit (RXB8) is used for identifying address and data frames. When
the frame type bit (the first stop or the ninth bit) is one, the frame contains an address. When the
frame type bit is zero the frame is a data frame.
The Multi-processor Communication mode enables several slave MCUs to receive data from a
Master MCU. This is done by first decoding an address frame to find out which MCU has been
Table 71. Recommended Maximum Receiver Baud Rate Error for Normal Speed Mode (U2X =
0)
D
# (Data+Parity Bit) Rslow (%) Rfast (%) Max. Total Error (%)
Recommended Max.
Receiver Error (%)
5 93.20 106.67 +6.67/-6.8% ± 3.0
6 94.12 105.79 +5.79/-5.88 ± 2.5
7 94.81 105.11 +5.11/-5.19 ± 2.0
8 95.36 104.58 +4.58/-4.54 ± 2.0
9 95.81 104.14 +4.14/-4.19 ± 1.5
10 96.17 103.78 +3.7 /-3.83 ± 1.5
Table 72. Recommended Maximum Receiver Baud Rate Error for Double Speed Mode (U2X =
1)
D
# (Data+Parity Bit) Rslow (%) Rfast (%) Max. Total Error (%)
Recommended Max.
Receiver Error (%)
5 94.12 105.66 +5.66/-5.88 ± 2.5
6 94.92 104.92 +4.92/-5.08 ± 2.0
7 95.52 104.35 +4.35/-4.48 ± 1.5
8 96.00 103.90 +3.90/-4.00 ± 1.5
9 96.39 103.53 +3.53/-3.61 ± 1.5
10 96.70 103.23 +3.23/-3.30 ± 1.0
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addressed. If a particular slave MCU has been addressed, it will receive the following data
frames as normal, while the other slave MCUs will ignore the received frames until another
address frame is received.
Using MPCM For an MCU to act as a Master MCU, it can use a 9-bit character frame format (UCSZ = 7). The
ninth bit (TXB8) must be set when an address frame (TXB8 = 1) or cleared when a data frame
(TXB = 0) is being transmitted. The slave MCUs must in this case be set to use a 9-bit character
frame format.
The following procedure should be used to exchange data in Multi-processor Communication
mode:
1. All Slave MCUs are in Multi-processor Communication mode (MPCM in UCSRA is set).
2. The Master MCU sends an address frame, and all slaves receive and read this frame. In
the slave MCUs, the RXC Flag in UCSRA will be set as normal.
3. Each Slave MCU reads the UDR Register and determines if it has been selected. If so, it
clears the MPCM bit in UCSRA, otherwise it waits for the next address byte and keeps
the MPCM setting.
4. The addressed MCU will receive all data frames until a new address frame is received.
The other Slave MCUs, which still have the MPCM bit set, will ignore the data frames.
5. When the last data frame is received by the addressed MCU, the addressed MCU sets
the MPCM bit and waits for a new address frame from master. The process then repeats
from 2.
Using any of the 5- to 8-bit character frame formats is possible, but impractical since the receiver
must change between using n and n+1 character frame formats. This makes full-duplex opera-
tion difficult since the Transmitter and Receiver uses the same character size setting. If 5 to 8 bit
character frames are used, the Transmitter must be set to use two stop bit (USBS = 1) since the
first stop bit is used for indicating the frame type.
Do not use Read-Modify-Write instructions (SBI and CBI) to set or clear the MPCM bit. The
MPCM bit shares the same I/O location as the TXC Flag and this might accidentally be cleared
when using SBI or CBI instructions.
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Accessing
UBRRH/
UCSRC Registers
The UBRRH Register shares the same I/O location as the UCSRC Register. Therefore some
special consideration must be taken when accessing this I/O location.
Write Access When doing a write access of this I/O location, the high bit of the value written, the USART Reg-
ister Select (URSEL) bit, controls which one of the two registers that will be written. If URSEL is
zero during a write operation, the UBRRH value will be updated. If URSEL is one, the UCSRC
setting will be updated.
The following code examples show how to access the two registers.
Note: 1. The example code assumes that the part specific header file is included.
As the code examples illustrate, write accesses of the two registers are relatively unaffected of
the sharing of I/O location.
Assembly Code Examples(1)
...
; Set UBRRH to 2
ldi r16,0x02
out UBRRH,r16
...
; Set the USBS and ?he UCSZ1 bit to one, and
; the remaining bit? to zero.
ldi r16,(1<<URSEL)|(1<<USBS)|(1<<UCSZ1)
out UCSRC,r16
...
C Code Examples(1)
...
/* Set UBRRH to 2 */
UBRRH = 0x02;
...
/* Set the USBS and?the UCSZ1 bit to one, and */
/* the remaining bi?s to zero. */
UCSRC = (1<<URSEL)|(1<<U?BS)|(1<<UCSZ1);
...
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Read Access Doing a read access to the UBRRH or the UCSRC Register is a more complex operation. How-
ever, in most applications, it is rarely necessary to read any of these registers.
The read access is controlled by a timed sequence. Reading the I/O location once returns the
UBRRH Register contents. If the register location was read in previous system clock cycle, read-
ing the register in the current clock cycle will return the UCSRC contents. Note that the timed
sequence for reading the UCSRC is an atomic operation. Interrupts must therefore be controlled
(e.g., by disabling interrupts globally) during the read operation.
The following code example shows how to read the UCSRC Register contents.
Note: 1. The example code assumes that the part specific header file is included.
The assembly code example returns the UCSRC value in r16.
Reading the UBRRH contents is not an atomic operation and therefore it can be read as an ordi-
nary register, as long as the previous instruction did not access the register location.
Assembly Code Example(1)
USART_ReadUCSRC:
; Read UCSRC
in r16,UBRRH
in r16,UCSRC
ret
C Code Example(1)
unsigned char USART_ReadUCSRC( void )
{
unsigned char ucsrc?
/* Read UCSRC ?/
ucsrc = UBRRH;
ucsrc = UCSRC;
return ucsrc;
}
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USART Register
Description
USART I/O Data
Register – UDR
The USART Transmit Data Buffer Register and USART Receive Data Buffer Registers share the
same I/O address referred to as USART Data Register or UDR. The Transmit Data Buffer Reg-
ister (TXB) will be the destination for data written to the UDR Register location. Reading the
UDR Register location will return the contents of the Receive Data Buffer Register (RXB).
For 5-, 6-, or 7-bit characters the upper unused bits will be ignored by the Transmitter and set to
zero by the Receiver.
The transmit buffer can only be written when the UDRE Flag in the UCSRA Register is set. Data
written to UDR when the UDRE Flag is not set, will be ignored by the USART Transmitter. When
data is written to the transmit buffer, and the Transmitter is enabled, the Transmitter will load the
data into the Transmit Shift Register when the Shift Register is empty. Then the data will be seri-
ally transmitted on the TxD pin.
The receive buffer consists of a two level FIFO. The FIFO will change its state whenever the
receive buffer is accessed. Due to this behavior of the receive buffer, do not use read modify
write instructions (SBI and CBI) on this location. Be careful when using bit test instructions (SBIC
and SBIS), since these also will change the state of the FIFO.
USART Control and
Status Register A –
UCSRA
• Bit 7 – RXC: USART Receive Complete
This flag bit is set when there are unread data in the receive buffer and cleared when the receive
buffer is empty (i.e., does not contain any unread data). If the receiver is disabled, the receive
buffer will be flushed and consequently the RXC bit will become zero. The RXC Flag can be
used to generate a Receive Complete interrupt (see description of the RXCIE bit).
• Bit 6 – TXC: USART Transmit Complete
This flag bit is set when the entire frame in the Transmit Shift Register has been shifted out and
there are no new data currently present in the transmit buffer (UDR). The TXC Flag bit is auto-
matically cleared when a transmit complete interrupt is executed, or it can be cleared by writing
a one to its bit location. The TXC Flag can generate a Transmit Complete interrupt (see descrip-
tion of the TXCIE bit).
• Bit 5 – UDRE: USART Data Register Empty
The UDRE Flag indicates if the transmit buffer (UDR) is ready to receive new data. If UDRE is
one, the buffer is empty, and therefore ready to be written. The UDRE Flag can generate a Data
Register Empty interrupt (see description of the UDRIE bit).
UDRE is set after a Reset to indicate that the transmitter is ready.
Bit 76543210
RXB[7:0] UDR (Read)
TXB[7:0] UDR (Write)
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
RXC TXC UDRE FE DOR UPE U2X MPCM UCSRA
Read/Write R R/W R R R R R/W R/W
Initial Value00100000
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• Bit 4 – FE: Frame Error
This bit is set if the next character in the receive buffer had a Frame Error when received. I.e.,
when the first stop bit of the next character in the receive buffer is zero. This bit is valid until the
receive buffer (UDR) is read. The FE bit is zero when the stop bit of received data is one. Always
set this bit to zero when writing to UCSRA.
• Bit 3 – DOR: Data OverRun
This bit is set if a Data OverRun condition is detected. A data overrun occurs when the receive
buffer is full (two characters), it is a new character waiting in the reCeive Shift Register, and a
new start bit is detected. This bit is valid until the receive buffer (UDR) is read. Always set this bit
to zero when writing to UCSRA.
• Bit 2 – UPE: Parity Error
This bit is set if the next character in the receive buffer had a Parity Error when received and the
Parity Checking was enabled at that point (UPM1 = 1). This bit is valid until the receive buffer
(UDR) is read. Always set this bit to zero when writing to UCSRA.
• Bit 1 – U2X: Double the USART Transmission Speed
This bit only has effect for the asynchronous operation. Write this bit to zero when using syn-
chronous operation.
Writing this bit to one will reduce the divisor of the baud rate divider from 16 to 8 effectively dou-
bling the transfer rate for asynchronous communication.
• Bit 0 – MPCM: Multi-processor Communication Mode
This bit enables the Multi-processor Communication mode. When the MPCM bit is written to
one, all the incoming frames received by the USART receiver that do not contain address infor-
mation will be ignored. The transmitter is unaffected by the MPCM setting. For more detailed
information see “Multi-processor Communication Mode” on page 182.
USART Control and
Status Register B –
UCSRB
• Bit 7 – RXCIE: RX Complete Interrupt Enable
Writing this bit to one enables interrupt on the RXC Flag. A USART Receive Complete interrupt
will be generated only if the RXCIE bit is written to one, the Global Interrupt Flag in SREG is writ-
ten to one and the RXC bit in UCSRA is set.
• Bit 6 – TXCIE: TX Complete Interrupt Enable
Writing this bit to one enables interrupt on the TXC Flag. A USART Transmit Complete interrupt
will be generated only if the TXCIE bit is written to one, the Global Interrupt Flag in SREG is writ-
ten to one and the TXC bit in UCSRA is set.
• Bit 5 – UDRIE: USART Data Register Empty Interrupt Enable
Writing this bit to one enables interrupt on the UDRE Flag. A Data Register Empty interrupt will
be generated only if the UDRIE bit is written to one, the Global Interrupt Flag in SREG is written
to one and the UDRE bit in UCSRA is set.
Bit 76543210
RXCIE TXCIE UDRIE RXEN TXEN UCSZ2 RXB8 TXB8 UCSRB
Read/Write R/W R/W R/W R/W R/W R/W R R/W
Initial Value00000000
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• Bit 4 – RXEN: Receiver Enable
Writing this bit to one enables the USART Receiver. The Receiver will override normal port oper-
ation for the RxD pin when enabled. Disabling the Receiver will flush the receive buffer
invalidating the FE, DOR and UPE Flags.
• Bit 3 – TXEN: Transmitter Enable
Writing this bit to one enables the USART Transmitter. The Transmitter will override normal port
operation for the TxD pin when enabled. The disabling of the Transmitter (writing TXEN to zero)
will not become effective until ongoing and pending transmissions are completed, i.e., when the
Transmit Shift Register and Transmit Buffer Register do not contain data to be transmitted.
When disabled, the Transmitter will no longer override the TxD port.
• Bit 2 – UCSZ2: Character Size
The UCSZ2 bits combined with the UCSZ1:0 bit in UCSRC sets the number of data bits (charac-
ter size) in a frame the Receiver and Transmitter use.
• Bit 1 – RXB8: Receive Data Bit 8
RXB8 is the ninth data bit of the received character when operating with serial frames with nine
data bits. Must be read before reading the low bits from UDR.
• Bit 0 – TXB8: Transmit Data Bit 8
TXB8 is the 9th data bit in the character to be transmitted when operating with serial frames with
9 data bits. Must be written before writing the low bits to UDR.
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USART Control and
Status Register C –
UCSRC(1)
Note: 1. The UCSRC Register shares the same I/O location as the UBRRH Register. See the “Access-
ing UBRRH/ UCSRC Registers” on page 184 section which describes how to access this
register.
• Bit 7 – URSEL: Register Select
This bit selects between accessing the UCSRC or the UBRRH Register. It is read as one when
reading UCSRC. The URSEL must be one when writing the UCSRC.
• Bit 6 – UMSEL: USART Mode Select
This bit selects between asynchronous and synchronous mode of operation.
• Bit 5:4 – UPM1:0: Parity Mode
These bits enable and set type of parity generation and check. If enabled, the transmitter will
automatically generate and send the parity of the transmitted data bits within each frame. The
receiver will generate a parity value for the incoming data and compare it to the UPM0 setting. If
a mismatch is detected, the UPE Flag in UCSRA will be set.
• Bit 3 – USBS: Stop Bit Select
This bit selects the number of stop bits to be inserted by the transmitter. The receiver ignores
this setting.
Bit 76543210
URSEL UMSEL UPM1 UPM0 USBS UCSZ1 UCSZ0 UCPOL UCSRC
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value10000110
Table 73. UMSEL Bit Settings
UMSEL Mode
0 Asynchronous Operation
1 Synchronous Operation
Table 74. UPM Bits Settings
UPM1 UPM0 Parity Mode
0 0 Disabled
01Reserved
1 0 Enabled, Even Parity
1 1 Enabled, Odd Parity
Table 75. USBS Bit Settings
USBS Stop Bit(s)
01-bit
12-bit
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• Bit 2:1 – UCSZ1:0: Character Size
The UCSZ1:0 bits combined with the UCSZ2 bit in UCSRB sets the number of data bits (Char-
acter Size) in a frame the receiver and transmitter use.
• Bit 0 – UCPOL: Clock Polarity
This bit is used for synchronous mode only. Write this bit to zero when asynchronous mode is
used. The UCPOL bit sets the relationship between data output change and data input sample,
and the synchronous clock (XCK).
USART Baud Rate
Registers – UBRRL
and UBRRH(1)
Note: 1. The UBRRH Register shares the same I/O location as the UCSRC Register. See the “Access-
ing UBRRH/ UCSRC Registers” on page 184 section which describes how to access this
register.
• Bit 15 – URSEL: Register Select
This bit selects between accessing the UBRRH or the UCSRC Register. It is read as zero when
reading UBRRH. The URSEL must be zero when writing the UBRRH.
• Bit 14:12 – Reserved Bits
These bits are reserved for future use. For compatibility with future devices, these bit must be
written to zero when UBRRH is written.
Table 76. UCSZ Bits Settings
UCSZ2 UCSZ1 UCSZ0 Character Size
0005-bit
0016-bit
0107-bit
0118-bit
100Reserved
101Reserved
110Reserved
1119-bit
Table 77. UCPOL Bit Settings
UCPOL
Transmitted Data Changed
(Output of TxD Pin)
Received Data Sampled
(Input on RxD Pin)
0 Rising XCK Edge Falling XCK Edge
1 Falling XCK Edge Rising XCK Edge
Bit 151413121110 9 8
URSEL – – – UBRR[11:8] UBRRH
UBRR[7:0] UBRRL
76543210
Read/Write R/W R R R R/W R/W R/W R/W
R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
00000000
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• Bit 11:0 – UBRR11:0: USART Baud Rate Register
This is a 12-bit register which contains the USART baud rate. The UBRRH contains the four
most significant bits, and the UBRRL contains the eight least significant bits of the USART baud
rate. Ongoing transmissions by the transmitter and receiver will be corrupted if the baud rate is
changed. Writing UBRRL will trigger an immediate update of the baud rate prescaler.
Examples of Baud
Rate Setting
For standard crystal and resonator frequencies, the most commonly used baud rates for asyn-
chronous operation can be generated by using the UBRR settings in Table 78. UBRR values
which yield an actual baud rate differing less than 0.5% from the target baud rate, are bold in the
table. Higher error ratings are acceptable, but the receiver will have less noise resistance when
the error ratings are high, especially for large serial frames (see “Asynchronous Operational
Range” on page 181). The error values are calculated using the following equation:
Error[%] BaudRateClosest Match
BaudRate
-------------------------------------------------------- 1–
⎝⎠
⎛⎞
100%•=
Table 78. Examples of UBRR Settings for Commonly Used Oscillator Frequencies
Baud
Rate
(bps)
fosc = 1.0000 MHz fosc = 1.8432 MHz fosc = 2.0000 MHz
U2X = 0 U2X = 1 U2X = 0 U2X = 1 U2X = 0 U2X = 1
UBRR Error UBRR Error UBRR Error UBRR Error UBRR Error UBRR Error
2400 250.2%510.2%470.0%950.0%510.2%1030.2%
4800 120.2%250.2%230.0%470.0%250.2%510.2%
9600 6 -7.0% 12 0.2% 11 0.0% 23 0.0% 12 0.2% 25 0.2%
14.4k 3 8.5% 8 -3.5% 7 0.0% 15 0.0% 8 -3.5% 16 2.1%
19.2k 2 8.5% 6 -7.0% 5 0.0% 11 0.0% 6 -7.0% 12 0.2%
28.8k 1 8.5% 3 8.5% 3 0.0% 7 0.0% 3 8.5% 8 -3.5%
38.4k 1 -18.6% 2 8.5% 2 0.0% 5 0.0% 2 8.5% 6 -7.0%
57.6k 0 8.5% 1 8.5% 1 0.0% 3 0.0% 1 8.5% 3 8.5%
76.8k – – 1 -18.6% 1 -25.0% 2 0.0% 1 -18.6% 2 8.5%
115.2k – – 0 8.5% 0 0.0% 1 0.0% 0 8.5% 1 8.5%
230.4k––––––00.0%––––
250k––––––––––00.0%
Max. (1) 62.5 kbps 125 kbps 115.2 kbps 230.4 kbps 125 kbps 250 kbps
1. UBRR = 0, Error = 0.0%
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Table 79. Examples of UBRR Settings for Commonly Used Oscillator Frequencies (Continued)
Baud
Rate
(bps)
fosc = 3.6864 MHz fosc = 4.0000 MHz fosc = 7.3728 MHz
U2X = 0 U2X = 1 U2X = 0 U2X = 1 U2X = 0 U2X = 1
UBRR Error UBRR Error UBRR Error UBRR Error UBRR Error UBRR Error
2400 95 0.0% 191 0.0% 103 0.2% 207 0.2% 191 0.0% 383 0.0%
4800 47 0.0% 95 0.0% 51 0.2% 103 0.2% 95 0.0% 191 0.0%
9600 230.0%470.0%250.2%510.2%470.0%950.0%
14.4k 15 0.0% 31 0.0% 16 2.1% 34 -0.8% 31 0.0% 63 0.0%
19.2k 11 0.0% 23 0.0% 12 0.2% 25 0.2% 23 0.0% 47 0.0%
28.8k 7 0.0% 15 0.0% 8 -3.5% 16 2.1% 15 0.0% 31 0.0%
38.4k 5 0.0% 11 0.0% 6 -7.0% 12 0.2% 11 0.0% 23 0.0%
57.6k 3 0.0% 7 0.0% 3 8.5% 8 -3.5% 7 0.0% 15 0.0%
76.8k 2 0.0% 5 0.0% 2 8.5% 6 -7.0% 5 0.0% 11 0.0%
115.2k 1 0.0% 3 0.0% 1 8.5% 3 8.5% 3 0.0% 7 0.0%
230.4k 0 0.0% 1 0.0% 0 8.5% 1 8.5% 1 0.0% 3 0.0%
250k 0 -7.8% 1 -7.8% 0 0.0% 1 0.0% 1 -7.8% 3 -7.8%
0.5M – – 0 -7.8% – – 0 0.0% 0 -7.8% 1 -7.8%
1M ––––––––––0-7.8%
Max. (1) 230.4 kbps 460.8 kbps 250 kbps 0.5 Mbps 460.8 kbps 921.6 kbps
1. UBRR = 0, Error = 0.0%
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Table 80. Examples of UBRR Settings for Commonly Used Oscillator Frequencies (Continued)
Baud
Rate
(bps)
fosc = 8.0000 MHz fosc = 11.0592 MHz fosc = 14.7456 MHz
U2X = 0 U2X = 1 U2X = 0 U2X = 1 U2X = 0 U2X = 1
UBRR Error UBRR Error UBRR Error UBRR Error UBRR Error UBRR Error
2400 207 0.2% 416 -0.1% 287 0.0% 575 0.0% 383 0.0% 767 0.0%
4800 103 0.2% 207 0.2% 143 0.0% 287 0.0% 191 0.0% 383 0.0%
9600 51 0.2% 103 0.2% 71 0.0% 143 0.0% 95 0.0% 191 0.0%
14.4k 34 -0.8% 68 0.6% 47 0.0% 95 0.0% 63 0.0% 127 0.0%
19.2k 25 0.2% 51 0.2% 35 0.0% 71 0.0% 47 0.0% 95 0.0%
28.8k 16 2.1% 34 -0.8% 23 0.0% 47 0.0% 31 0.0% 63 0.0%
38.4k 12 0.2% 25 0.2% 17 0.0% 35 0.0% 23 0.0% 47 0.0%
57.6k 8 -3.5% 16 2.1% 11 0.0% 23 0.0% 15 0.0% 31 0.0%
76.8k 6 -7.0% 12 0.2% 8 0.0% 17 0.0% 11 0.0% 23 0.0%
115.2k 3 8.5% 8 -3.5% 5 0.0% 11 0.0% 7 0.0% 15 0.0%
230.4k 1 8.5% 3 8.5% 2 0.0% 5 0.0% 3 0.0% 7 0.0%
250k 1 0.0% 3 0.0% 2 -7.8% 5 -7.8% 3 -7.8% 6 5.3%
0.5M 0 0.0% 1 0.0% – – 2 -7.8% 1 -7.8% 3 -7.8%
1M – – 0 0.0% – – – – 0 -7.8% 1 -7.8%
Max. (1) 0.5 Mbps 1 Mbps 691.2 kbps 1.3824 Mbps 921.6 kbps 1.8432 Mbps
1. UBRR = 0, Error = 0.0%
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Table 81. Examples of UBRR Settings for Commonly Used Oscillator Frequencies (Continued)
Baud
Rate
(bps)
fosc = 16.0000 MHz fosc = 18.4320 MHz fosc = 20.0000 MHz
U2X = 0 U2X = 1 U2X = 0 U2X = 1 U2X = 0 U2X = 1
UBRR Error UBRR Error UBRR Error UBRR Error UBRR Error UBRR Error
2400 416 -0.1% 832 0.0% 479 0.0% 959 0.0% 520 0.0% 1041 0.0%
4800 207 0.2% 416 -0.1% 239 0.0% 479 0.0% 259 0.2% 520 0.0%
9600 103 0.2% 207 0.2% 119 0.0% 239 0.0% 129 0.2% 259 0.2%
14.4k 68 0.6% 138 -0.1% 79 0.0% 159 0.0% 86 -0.2% 173 -0.2%
19.2k 51 0.2% 103 0.2% 59 0.0% 119 0.0% 64 0.2% 129 0.2%
28.8k 34 -0.8% 68 0.6% 39 0.0% 79 0.0% 42 0.9% 86 -0.2%
38.4k 25 0.2% 51 0.2% 29 0.0% 59 0.0% 32 -1.4% 64 0.2%
57.6k 16 2.1% 34 -0.8% 19 0.0% 39 0.0% 21 -1.4% 42 0.9%
76.8k 12 0.2% 25 0.2% 14 0.0% 29 0.0% 15 1.7% 32 -1.4%
115.2k 8 -3.5% 16 2.1% 9 0.0% 19 0.0% 10 -1.4% 21 -1.4%
230.4k 3 8.5% 8 -3.5% 4 0.0% 9 0.0% 4 8.5% 10 -1.4%
250k 3 0.0% 7 0.0% 4 -7.8% 8 2.4% 4 0.0% 9 0.0%
0.5M 1 0.0% 3 0.0% – – 4 -7.8% – – 4 0.0%
1M 0 0.0% 1 0.0% – – – – – – – –
Max. (1) 1 Mbps 2 Mbps 1.152 Mbps 2.304 Mbps 1.25 Mbps 2.5 Mbps
1. UBRR = 0, Error = 0.0%
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Analog
Comparator
The Analog Comparator compares the input values on the positive pin AIN0 and negative pin
AIN1. When the voltage on the positive pin AIN0 is higher than the voltage on the negative pin
AIN1, the Analog Comparator Output, ACO, is set. The comparator’s output can be set to trigger
the Timer/Counter1 Input Capture function. In addition, the comparator can trigger a separate
interrupt, exclusive to the Analog Comparator. The user can select Interrupt triggering on com-
parator output rise, fall or toggle. A block diagram of the comparator and its surrounding logic is
shown in Figure 82.
Figure 82. Analog Comparator Block Diagram(1)
Note: 1. Refer to Figure 1 on page 2 and Table 32 on page 72 for Analog Comparator pin placement.
Analog Comparator
Control and Status
Register – ACSR
• Bit 7 – ACD: Analog Comparator Disable
When this bit is written logic one, the power to the Analog Comparator is switched off. This bit
can be set at any time to turn off the Analog Comparator. This will reduce power consumption in
Active and Idle mode. When changing the ACD bit, the Analog Comparator Interrupt must be
disabled by clearing the ACIE bit in ACSR. Otherwise an interrupt can occur when the bit is
changed.
• Bit 6 – ACBG: Analog Comparator Bandgap Select
When this bit is set, a fixed bandgap reference voltage replaces the positive input to the Analog
Comparator. When this bit is cleared, AIN0 is applied to the positive input of the Analog Compar-
ator. When the bandgap reference is used as input to the Analog Comparator, it will take a
certain time for the voltage to stabilize. If not stibilized, the first conversion may give a wrong
value. See “Internal Voltage Reference” on page 52.
• Bit 5 – ACO: Analog Comparator Output
The output of the Analog Comparator is synchronized and then directly connected to ACO. The
synchronization introduces a delay of 1 - 2 clock cycles.
ACBG
BANDGAP
REFERENCE
Bit 76543210
ACD ACBG ACO ACI ACIE ACIC ACIS1 ACIS0 ACSR
Read/Write R/W R/W R R/W R/W R/W R/W R/W
Initial Value00N/A00000
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• Bit 4 – ACI: Analog Comparator Interrupt Flag
This bit is set by hardware when a comparator output event triggers the interrupt mode defined
by ACIS1 and ACIS0. The Analog Comparator interrupt routine is executed if the ACIE bit is set
and the I-bit in SREG is set. ACI is cleared by hardware when executing the corresponding inter-
rupt handling vector. Alternatively, ACI is cleared by writing a logic one to the flag.
• Bit 3 – ACIE: Analog Comparator Interrupt Enable
When the ACIE bit is written logic one and the I-bit in the Status Register is set, the Analog Com-
parator interrupt is activated. When written logic zero, the interrupt is disabled.
• Bit 2 – ACIC: Analog Comparator Input Capture Enable
When written logic one, this bit enables the Input Capture function in Timer/Counter1 to be trig-
gered by the Analog Comparator. The comparator output is in this case directly connected to the
Input Capture front-end logic, making the comparator utilize the noise canceler and edge select
features of the Timer/Counter1 Input Capture interrupt. When written logic zero, no connection
between the Analog Comparator and the Input Capture function exists. To make the comparator
trigger the Timer/Counter1 Input Capture interrupt, the TICIE1 bit in the Timer Interrupt Mask
Register (TIMSK) must be set.
• Bits 1, 0 – ACIS1, ACIS0: Analog Comparator Interrupt Mode Select
These bits determine which comparator events that trigger the Analog Comparator interrupt. The
different settings are shown in Table 82.
When changing the ACIS1/ACIS0 bits, the Analog Comparator Interrupt must be disabled by
clearing its Interrupt Enable bit in the ACSR Register. Otherwise an interrupt can occur when the
bits are changed.
Table 82. ACIS1/ACIS0 Settings
ACIS1 ACIS0 Interrupt Mode
0 0 Comparator Interrupt on Output Toggle.
01Reserved
1 0 Comparator Interrupt on Falling Output Edge.
1 1 Comparator Interrupt on Rising Output Edge.
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JTAG Interface
and On-chip
Debug System
Features •JTAG (IEEE std. 1149.1 Compliant) Interface
•Boundary-scan Capabilities According to the IEEE std. 1149.1 (JTAG) Standard
•Debugger Access to:
– All Internal Peripheral Units
– Internal and External RAM
– The Internal Register File
– Program Counter
– EEPROM and Flash Memories
•Extensive On-chip Debug Support for Break Conditions, Including
– AVR Break Instruction
– Break on Change of Program Memory Flow
– Single Step Break
– Program Memory Breakpoints on Single Address or Address Range
– Data Memory Breakpoints on Single Address or Address Range
•Programming of Flash, EEPROM, Fuses, and Lock Bits through the JTAG Interface
•On-chip Debugging Supported by AVR Studio®
Overview The AVR IEEE std. 1149.1 compliant JTAG interface can be used for
• Testing PCBs by using the JTAG Boundary-scan capability.
• Programming the non-volatile memories, Fuses and Lock bits.
• On-chip debugging.
A brief description is given in the following sections. Detailed descriptions for Programming via
the JTAG interface, and using the Boundary-scan Chain can be found in the sections “Program-
ming via the JTAG Interface” on page 250 and “IEEE 1149.1 (JTAG) Boundary-scan” on page
204, respectively. The On-chip Debug support is considered being private JTAG instructions,
and distributed within ATMEL and to selected third party vendors only.
Figure 83 shows a block diagram of the JTAG interface and the On-chip Debug system. The
TAP Controller is a state machine controlled by the TCK and TMS signals. The TAP Controller
selects either the JTAG Instruction Register or one of several Data Registers as the scan chain
(Shift Register) between the TDI – input and TDO – output. The Instruction Register holds JTAG
instructions controlling the behavior of a Data Register.
The ID-Register, Bypass Register, and the Boundary-scan Chain are the Data Registers used
for board-level testing. The JTAG Programming Interface (actually consisting of several physical
and virtual Data Registers) is used for serial programming via the JTAG interface. The Internal
Scan Chain and Break Point Scan Chain are used for On-chip debugging only.
Test Access Port –
TAP
The JTAG interface is accessed through four of the AVR’s pins. In JTAG terminology, these pins
constitute the Test Access Port – TAP. These pins are:
• TMS: Test mode select. This pin is used for navigating through the TAP-controller state
machine.
• TCK: Test Clock. JTAG operation is synchronous to TCK.
• TDI: Test Data In. Serial input data to be shifted in to the Instruction Register or Data
Register (Scan Chains).
• TDO: Test Data Out. Serial output data from Instruction Register or Data Register.
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The IEEE std. 1149.1 also specifies an optional TAP signal; TRST – Test ReSeT – which is not
provided.
When the JTAGEN fuse is unprogrammed, these four TAP pins are normal port pins and the
TAP controller is in reset. When programmed and the JTD bit in MCUCSR is cleared, the TAP
input signals are internally pulled high and the JTAG is enabled for Boundary-scan and program-
ming. In this case, the TAP output pin (TDO) is left floating in states where the JTAG TAP
controller is not shifting data, and must therefore be connected to a pull-up resistor or other
hardware having pull-ups (for instance the TDI-input of the next device in the scan chain). The
device is shipped with this fuse programmed.
For the On-chip Debug system, in addition to the JTAG interface pins, the RESET pin is moni-
tored by the debugger to be able to detect External Reset sources. The debugger can also pull
the RESET pin low to reset the whole system, assuming only open collectors on the reset line
are used in the application.
Figure 83. Block Diagram
TAP
CONTROLLER
TDI
TDO
TCK
TMS
FLASH
MEMORY
AVR CPU
DIGITAL
PERIPHERAL
UNITS
JTAG / AVR CORE
COMMUNICATION
INTERFACE
BREAKPOINT
UNIT FLOW CONTROL
UNIT
OCD STATUS
AND CONTROL
INTERNAL
SCAN
CHAIN
M
U
X
INSTRUCTION
REGISTER
ID
REGISTER
BYPASS
REGISTER
JTAG PROGRAMMING
INTERFACE
PC
Instruction
Address
Data
BREAKPOINT
SCAN CHAIN
ADDRESS
DECODER
ANALOG
PERIPHERIAL
UNITS
I/O PORT 0
I/O PORT n
BOUNDARY SCAN CHAIN
Analog inputs
Control & Clock lines
DEVICE BOUNDARY
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Figure 84. TAP Controller State Diagram
Test-Logic-Reset
Run-Test/Idle
Shift-DR
Exit1-DR
Pause-DR
Exit2-DR
Update-DR
Select-IR Scan
Capture-IR
Shift-IR
Exit1-IR
Pause-IR
Exit2-IR
Update-IR
Select-DR Scan
Capture-DR
0
1
011 1
00
00
11
10
1
1
0
1
0
0
10
1
1
0
1
0
0
00
11
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TAP Controller The TAP controller is a 16-state finite state machine that controls the operation of the Boundary-
scan circuitry, JTAG programming circuitry, or On-chip Debug system. The state transitions
depicted in Figure 84 depend on the signal present on TMS (shown adjacent to each state tran-
sition) at the time of the rising edge at TCK. The initial state after a Power-on Reset is Test-
Logic-Reset.
As a definition in this document, the LSB is shifted in and out first for all Shift Registers.
Assuming Run-Test/Idle is the present state, a typical scenario for using the JTAG interface is:
• At the TMS input, apply the sequence 1, 1, 0, 0 at the rising edges of TCK to enter the Shift
Instruction Register – Shift-IR state. While in this state, shift the four bits of the JTAG
instructions into the JTAG Instruction Register from the TDI input at the rising edge of TCK.
The TMS input must be held low during input of the 3 LSBs in order to remain in the Shift-IR
state. The MSB of the instruction is shifted in when this state is left by setting TMS high.
While the instruction is shifted in from the TDI pin, the captured IR-state 0x01 is shifted out
on the TDO pin. The JTAG Instruction selects a particular Data Register as path between
TDI and TDO and controls the circuitry surrounding the selected Data Register.
• Apply the TMS sequence 1, 1, 0 to re-enter the Run-Test/Idle state. The instruction is
latched onto the parallel output from the Shift Register path in the Update-IR state. The Exit-
IR, Pause-IR, and Exit2-IR states are only used for navigating the state machine.
• At the TMS input, apply the sequence 1, 0, 0 at the rising edges of TCK to enter the Shift
Data Register – Shift-DR state. While in this state, upload the selected data register
(selected by the present JTAG instruction in the JTAG Instruction Register) from the TDI
input at the rising edge of TCK. In order to remain in the Shift-DR state, the TMS input must
be held low during input of all bits except the MSB. The MSB of the data is shifted in when
this state is left by setting TMS high. While the Data Register is shifted in from the TDI pin,
the parallel inputs to the Data Register captured in the Capture-DR state is shifted out on the
TDO pin.
• Apply the TMS sequence 1, 1, 0 to re-enter the Run-Test/Idle state. If the selected data
register has a latched parallel-output, the latching takes place in the Update-DR state. The
Exit-DR, Pause-DR, and Exit2-DR states are only used for navigating the state machine.
As shown in the state diagram, the Run-Test/Idle state need not be entered between selecting
JTAG instruction and using Data Registers, and some JTAG instructions may select certain
functions to be performed in the Run-Test/Idle, making it unsuitable as an Idle state.
Note: Independent of the initial state of the TAP Controller, the Test-Logic-Reset state can always be
entered by holding TMS high for five TCK clock periods.
For detailed information on the JTAG specification, refer to the literature listed in “Bibliography”
on page 203.
Using the
Boundary-scan
Chain
A complete description of the Boundary-scan capabilities are given in the section “IEEE 1149.1
(JTAG) Boundary-scan” on page 204.
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Using the On-chip
Debug system
As shown in Figure 83, the hardware support for On-chip Debugging consists mainly of
• A scan chain on the interface between the internal AVR CPU and the internal peripheral
units
• Break Point unit
• Communication interface between the CPU and JTAG system
All read or modify/write operations needed for implementing the Debugger are done by applying
AVR instructions via the internal AVR CPU Scan Chain. The CPU sends the result to an I/O
memory mapped location which is part of the communication interface between the CPU and the
JTAG system.
The Break Point unit implements Break on Change of program flow, Single Step Break, two Pro-
gram memory Break Points, and two Combined Break Points. Together, the four Break Points
can be configured as either:
• 4 single Program Memory Break Points
• 3 Single Program Memory Break Point + 1 single Data Memory Break Point
• 2 single Program Memory Break Points + 2 single Data Memory Break Points
• 2 single Program Memory Break Points + 1 Program Memory Break Point with mask (“range
Break Point”)
• 2 single Program Memory Break Points + 1 Data Memory Break Point with mask (“range
Break Point”)
A debugger, like the AVR Studio®, may however use one or more of these resources for its inter-
nal purpose, leaving less flexibility to the end-user.
A list of the On-chip Debug specific JTAG instructions is given in “On-chip debug specific JTAG
instructions” on page 202.
The JTAGEN Fuse must be programmed to enable the JTAG Test Access Port. In addition, the
OCDEN Fuse must be programmed and no Lock bits must be set for the On-chip debug system
to work. As a security feature, the On-chip debug system is disabled when either of the LB1 or
LB2 Lock bits are set. Otherwise, the On-chip debug system would have provided a backdoor
into a secured device.
The AVR Studio enables the user to fully control execution of programs on an AVR device with
On-chip Debug capability, AVR In-Circuit Emulator, or the built-in AVR Instruction Set Simulator.
AVR Studio supports source level execution of Assembly programs assembled with Atmel Cor-
poration’s AVR Assembler and C programs compiled with third party vendors’ compilers.
AVR Studio runs under Microsoft® Windows® 95/98/2000, Windows NT®, and Windows XP®.
For a full description of the AVR Studio, please refer to the AVR Studio User Guide. Only high-
lights are presented in this document.
All necessary execution commands are available in AVR Studio, both on source level and on
disassembly level. The user can execute the program, single step through the code either by
tracing into or stepping over functions, step out of functions, place the cursor on a statement and
execute until the statement is reached, stop the execution, and reset the execution target. In
addition, the user can have an unlimited number of code Break Points (using the BREAK
instruction) and up to two data memory Break Points, alternatively combined as a mask (range)
Break Point.
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On-chip debug
specific JTAG
instructions
The On-chip debug support is considered being private JTAG instructions, and distributed within
ATMEL and to selected 3rd party vendors only. Instruction opcodes are listed for reference.
PRIVATE0; 0x8 Private JTAG instruction for accessing On-chip debug system.
PRIVATE1; 0x9 Private JTAG instruction for accessing On-chip debug system.
PRIVATE2; 0xA Private JTAG instruction for accessing On-chip debug system.
PRIVATE3; 0xB Private JTAG instruction for accessing On-chip debug system.
On-chip Debug
Related Register in
I/O Memory
On-chip Debug
Register – OCDR
The OCDR Register provides a communication channel from the running program in the micro-
controller to the debugger. The CPU can transfer a byte to the debugger by writing to this
location. At the same time, an internal flag; I/O Debug Register Dirty – IDRD – is set to indicate
to the debugger that the register has been written. When the CPU reads the OCDR Register the
7 LSB will be from the OCDR Register, while the MSB is the IDRD bit. The debugger clears the
IDRD bit when it has read the information.
In some AVR devices, this register is shared with a standard I/O location. In this case, the OCDR
Register can only be accessed if the OCDEN Fuse is programmed, and the debugger enables
access to the OCDR Register. In all other cases, the standard I/O location is accessed.
Refer to the debugger documentation for further information on how to use this register.
Using the JTAG
Programming
Capabilities
Programming of AVR parts via JTAG is performed via the 4-pin JTAG port, TCK, TMS, TDI and
TDO. These are the only pins that need to be controlled/observed to perform JTAG program-
ming (in addition to power pins). It is not required to apply 12V externally. The JTAGEN Fuse
must be programmed and the JTD bit in the MCUSR Register must be cleared to enable the
JTAG Test Access Port.
The JTAG programming capability supports:
• Flash programming and verifying.
• EEPROM programming and verifying.
• Fuse programming and verifying.
• Lock bit programming and verifying.
The Lock bit security is exactly as in parallel programming mode. If the Lock bits LB1 or LB2 are
programmed, the OCDEN Fuse cannot be programmed unless first doing a chip erase. This is a
security feature that ensures no backdoor exists for reading out the content of a secured device.
The details on programming through the JTAG interface and programming specific JTAG
instructions are given in the section “Programming via the JTAG Interface” on page 250.
Bit 7 6543210
MSB/IDRD LSB OCDR
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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Bibliography For more information about general Boundary-scan, the following literature can be consulted:
• IEEE: IEEE Std. 1149.1-1990. IEEE Standard Test Access Port and Boundary-scan
Architecture, IEEE, 1993
• Colin Maunder: The Board Designers Guide to Testable Logic Circuits, Addison-Wesley,
1992
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IEEE 1149.1
(JTAG)
Boundary-scan
Features •JTAG (IEEE std. 1149.1 Compliant) Interface
•Boundary-scan Capabilities According to the JTAG Standard
•Full Scan of all Port Functions as well as Analog Circuitry Having Off-chip Connections
•Supports the Optional IDCODE Instruction
•Additional Public AVR_RESET Instruction to Reset the AVR
System Overview The Boundary-scan chain has the capability of driving and observing the logic levels on the digi-
tal I/O pins, as well as the boundary between digital and analog logic for analog circuitry having
Off-chip connections. At system level, all ICs having JTAG capabilities are connected serially by
the TDI/TDO signals to form a long Shift Register. An external controller sets up the devices to
drive values at their output pins, and observe the input values received from other devices. The
controller compares the received data with the expected result. In this way, Boundary-scan pro-
vides a mechanism for testing interconnections and integrity of components on Printed Circuits
Boards by using the four TAP signals only.
The four IEEE 1149.1 defined mandatory JTAG instructions IDCODE, BYPASS, SAMPLE/PRE-
LOAD, and EXTEST, as well as the AVR specific public JTAG instruction AVR_RESET can be
used for testing the Printed Circuit Board. Initial scanning of the Data Register path will show the
ID-code of the device, since IDCODE is the default JTAG instruction. It may be desirable to have
the AVR device in Reset during Test mode. If not Reset, inputs to the device may be determined
by the scan operations, and the internal software may be in an undetermined state when exiting
the test mode. Entering Reset, the outputs of any Port Pin will instantly enter the high impedance
state, making the HIGHZ instruction redundant. If needed, the BYPASS instruction can be
issued to make the shortest possible scan chain through the device. The device can be set in
the Reset state either by pulling the external RESET pin low, or issuing the AVR_RESET
instruction with appropriate setting of the Reset Data Register.
The EXTEST instruction is used for sampling external pins and loading output pins with data.
The data from the output latch will be driven out on the pins as soon as the EXTEST instruction
is loaded into the JTAG IR-Register. Therefore, the SAMPLE/PRELOAD should also be used for
setting initial values to the scan ring, to avoid damaging the board when issuing the EXTEST
instruction for the first time. SAMPLE/PRELOAD can also be used for taking a snapshot of the
external pins during normal operation of the part.
The JTAGEN Fuse must be programmed and the JTD bit in the I/O Register MCUCSR must be
cleared to enable the JTAG Test Access Port.
When using the JTAG interface for Boundary-scan, using a JTAG TCK clock frequency higher
than the internal chip frequency is possible. The chip clock is not required to run.
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Data Registers The data registers relevant for Boundary-scan operations are:
• Bypass Register
• Device Identification Register
• Reset Register
• Boundary-scan Chain
Bypass Register The Bypass Register consists of a single Shift Register stage. When the Bypass Register is
selected as path between TDI and TDO, the register is reset to 0 when leaving the Capture-DR
controller state. The Bypass Register can be used to shorten the scan chain on a system when
the other devices are to be tested.
Device Identification
Register
Figure 85 shows the structure of the Device Identification Register.
Figure 85. The Format of the Device Identification Register
Version Version is a 4-bit number identifying the revision of the component. The JTAG version number
follows the revision of the device. Revision A is 0x0, revision B is 0x1 and so on.
Part Number The part number is a 16-bit code identifying the component. The JTAG Part Number for
ATmega162 is listed in Table 83.
Manufacturer ID The Manufacturer ID is a 11-bit code identifying the manufacturer. The JTAG manufacturer ID
for ATMEL is listed in Table 84.
Reset Register The Reset Register is a test data register used to reset the part. Since the AVR tri-states Port
Pins when reset, the Reset Register can also replace the function of the unimplemented optional
JTAG instruction HIGHZ.
A high value in the Reset Register corresponds to pulling the external Reset low. The part is
reset as long as there is a high value present in the Reset Register. Depending on the Fuse set-
tings for the clock options, the part will remain reset for a Reset Time-out Period (refer to “Clock
Sources” on page 36) after releasing the Reset Register. The output from this data register is not
latched, so the reset will take place immediately, as shown in Figure 86.
MSB LSB
Bit 31 28 27 12 11 1 0
Device ID Version Part Number Manufacturer ID 1
4 bits 16 bits 11 bits 1 bit
Table 83. AVR JTAG Part Number
Part number JTAG Part Number (Hex)
ATmega162 0x9404
Table 84. Manufacturer ID
Manufacturer JTAG Man. ID (Hex)
ATMEL 0x01F
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Figure 86. Reset Register
Boundary-scan Chain The Boundary-scan Chain has the capability of driving and observing the logic levels on the dig-
ital I/O pins, as well as the boundary between digital and analog logic for analog circuitry having
Off-chip connections.
See “Boundary-scan Chain” on page 208 for a complete description.
Boundary-scan
Specific JTAG
Instructions
The Instruction Register is 4-bit wide, supporting up to 16 instructions. Listed below are the
JTAG instructions useful for Boundary-scan operation. Note that the optional HIGHZ instruction
is not implemented, but all outputs with tri-state capability can be set in high-impedant state by
using the AVR_RESET instruction, since the initial state for all port pins is tri-state.
As a definition in this datasheet, the LSB is shifted in and out first for all Shift Registers.
The OPCODE for each instruction is shown behind the instruction name in hex format. The text
describes which Data Register is selected as path between TDI and TDO for each instruction.
EXTEST; 0x0 Mandatory JTAG instruction for selecting the Boundary-scan Chain as Data Register for testing
circuitry external to the AVR package. For port-pins, Pull-up Disable, Output Control, Output
Data, and Input Data are all accessible in the scan chain. For analog circuits having Off-chip
connections, the interface between the analog and the digital logic is in the scan chain. The con-
tents of the latched outputs of the Boundary-scan chain is driven out as soon as the JTAG IR-
Register is loaded with the EXTEST instruction.
The active states are:
• Capture-DR: Data on the external pins are sampled into the Boundary-scan Chain.
• Shift-DR: The Internal Scan Chain is shifted by the TCK input.
• Update-DR: Data from the scan chain is applied to output pins.
DQ
From
TDI
ClockDR · AVR_RESET
To
TDO
From Other Internal and
External Reset Sources
Internal Reset
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IDCODE; 0x1 Optional JTAG instruction selecting the 32-bit ID-register as data register. The ID-Register con-
sists of a version number, a device number and the manufacturer code chosen by JEDEC. This
is the default instruction after Power-up.
The active states are:
• Capture-DR: Data in the IDCODE Register is sampled into the Boundary-scan Chain.
• Shift-DR: The IDCODE scan chain is shifted by the TCK input.
SAMPLE_PRELOAD;
0x2
Mandatory JTAG instruction for preloading the output latches and taking a snapshot of the
input/output pins without affecting the system operation. However, the output latches are not
connected to the pins. The Boundary-scan Chain is selected as Data Register.
The active states are:
• Capture-DR: Data on the external pins are sampled into the Boundary-scan Chain.
• Shift-DR: The Boundary-scan Chain is shifted by the TCK input.
• Update-DR: Data from the Boundary-scan chain is applied to the output latches. However,
the output latches are not connected to the pins.
AVR_RESET; 0xC The AVR specific public JTAG instruction for forcing the AVR device into the Reset mode or
releasing the JTAG Reset source. The TAP controller is not reset by this instruction. The one bit
Reset Register is selected as data register. Note that the reset will be active as long as there is
a logic 'one' in the Reset Chain. The output from this chain is not latched.
The active states are:
• Shift-DR: The Reset Register is shifted by the TCK input.
BYPASS; 0xF Mandatory JTAG instruction selecting the Bypass Register for data register.
The active states are:
• Capture-DR: Loads a logic “0” into the Bypass Register.
• Shift-DR: The Bypass Register cell between TDI and TDO is shifted.
Boundary-scan
Related Register in I/O
Memory
MCU Control and
Status Register –
MCUCSR
The MCU Control and Status Register contains control bits for general MCU functions, and pro-
vides information on which reset source caused an MCU Reset.
• Bit 7 – JTD: JTAG Interface Disable
When this bit is zero, the JTAG interface is enabled if the JTAGEN Fuse is programmed. If this
bit is one, the JTAG interface is disabled. In order to avoid unintentional disabling or enabling of
the JTAG interface, a timed sequence must be followed when changing this bit: The application
software must write this bit to the desired value twice within four cycles to change its value.
If the JTAG interface is left unconnected to other JTAG circuitry, the JTD bit should be set to
one. The reason for this is to avoid static current at the TDO pin in the JTAG interface.
Bit 76543210
JTD –SM2 JTRF WDRF BORF EXTRF PORF MCUCSR
Read/Write R/W R/W R R/W R/W R/W R/W R/W
Initial Value 0 0 0 See Bit Description
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• Bit 4 – JTRF: JTAG Reset Flag
This bit is set if a reset is being caused by a logic one in the JTAG Reset Register selected by
the JTAG instruction AVR_RESET. This bit is reset by a Power-on Reset, or by writing a logic
zero to the flag.
Boundary-scan
Chain
The Boundary-scan Chain has the capability of driving and observing the logic levels on the dig-
ital I/O pins, as well as the boundary between digital and analog logic for analog circuitry having
Off-chip connection.
Scanning the Digital
Port Pins
Figure 87 shows the Boundary-scan Cell for a bi-directional port pin with pull-up function. The
cell consists of a standard Boundary-scan cell for the Pull-up Enable – PUExn – function, and a
bi-directional pin cell that combines the three signals Output Control – OCxn, Output Data –
ODxn, and Input Data – IDxn, into only a two-stage Shift Register. The port and pin indexes are
not used in the following description
The Boundary-scan logic is not included in the figures in the datasheet. Figure 88 shows a sim-
ple digital Port Pin as described in the section “I/O-Ports” on page 63. The Boundary-scan
details from Figure 87 replaces the dashed box in Figure 88.
When no alternate port function is present, the Input Data – ID – corresponds to the PINxn Reg-
ister value (but ID has no synchronizer), Output Data corresponds to the PORT Register, Output
Control corresponds to the Data Direction – DD Register, and the Pull-up Enable – PUExn – cor-
responds to logic expression PUD · DDxn · PORTxn.
Digital alternate port functions are connected outside the dotted box in Figure 88 to make the
scan chain read the actual pin value. For Analog function, there is a direct connection from the
external pin to the analog circuit, and a scan chain is inserted on the interface between the digi-
tal logic and the analog circuitry.
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Figure 87. Boundary-scan Cell for Bi-directional Port Pin with Pull-up Function.
DQ DQ
G
0
1
0
1
DQ DQ
G
0
1
0
1
0
1
0
1
DQ DQ
G
0
1
Port Pin (PXn)
VccEXTESTTo Next CellShiftDR
Output Control (OC)
Pullup Enable (PUE)
Output Data (OD)
Input Data (ID)
From Last Cell UpdateDRClockDR
FF2 LD2
FF1 LD1
LD0FF0
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Figure 88. General Port Pin Schematic Diagram
Scanning the RESET
pin
The RESET pin accepts 5V active low logic for standard reset operation, and 12V active high
logic for high voltage parallel programming. An observe-only cell as shown in Figure 89 is
inserted both for the 5V reset signal; RSTT, and the 12V reset signal; RSTHV.
Figure 89. Observe-only Cell
CLK
RPx
RRx
WRx
RDx
WDx
PUD
SYNCHRONIZER
WDx: WRITE DDRx
WRx: WRITE PORTx
RRx: READ PORTx REGISTER
RPx: READ PORTx PIN
PUD: PULLUP DISABLE
CLK : I/O CLOCK
RDx: READ DDRx
D
L
Q
Q
RESET
RESET
Q
Q
D
Q
QD
CLR
PORTxn
Q
QD
CLR
DDxn
PINxn
DATA BU S
SLEEP
SLEEP: SLEEP CONTROL
Pxn
I/O
I/O
See Boundary-Scan Description
for Details!
PUExn
OCxn
ODxn
IDxn
PUExn: PULLUP ENABLE for pin Pxn
OCxn: OUTPUT CONTROL for pin Pxn
ODxn: OUTPUT DATA to pin Pxn
IDxn: INPUT DATA from pin Pxn
0
1
DQ
From
Previous
Cell
ClockDR
ShiftDR
To
Next
Cell
From System Pin To System Logic
FF1
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Scanning the Clock
Pins
The AVR devices have many clock options selectable by fuses. These are: Internal RC Oscilla-
tor, External Clock, (High Frequency) Crystal Oscillator, Low Frequency Crystal Oscillator, and
Ceramic Resonator.
Figure 90 shows how each Oscillator with external connection is supported in the scan chain.
The Enable signal is supported with a general Boundary-scan cell, while the Oscillator/clock out-
put is attached to an observe-only cell. In addition to the main clock, the Timer Oscillator is
scanned in the same way. The output from the internal RC Oscillator is not scanned, as this
Oscillator does not have external connections.
Figure 90. Boundary-scan Cells for Oscillators and Clock Options
Table 85 summaries the scan registers for the external clock pin XTAL1, oscillators with
XTAL1/XTAL2 connections as well as 32 kHz Timer Oscillator.
Notes: 1. Do not enable more than one clock source as main clock at a time.
2. Scanning an Oscillator output gives unpredictable results as there is a frequency drift between
the Internal Oscillator and the JTAG TCK clock. If possible, scanning an external clock is
preferred.
3. The clock configuration is programmed by fuses. As a fuse is not changed run-time, the clock
configuration is considered fixed for a given application. The user is advised to scan the same
clock option as to be used in the final system. The enable signals are supported in the scan
chain because the system logic can disable clock options in sleep modes, thereby disconnect-
ing the Oscillator pins from the scan path if not provided. The INTCAP selection is not
supported in the scan-chain, so the boundary scan chain can not make a XTAL Oscillator
requiring internal capacitors to run unless the fuses are correctly programmed.
Table 85. Scan Signals for the Oscillator(1)(2)(3)
Enable Signal Scanned Clock Line Clock Option
Scanned Clock
Line when Not
Used
EXTCLKEN EXTCLK (XTAL1) External Clock 0
OSCON OSCCK External Crystal
External Ceramic Resonator
0
OSC32EN OSC32CK Low Freq. External Crystal 0
TOSKON TOSCK 32 kHz Timer Oscillator 0
0
1
DQ
From
Previous
Cell
ClockDR
ShiftDR
To
Next
Cell
To System Logic
FF1
0
1
DQ DQ
G
0
1
From
Previous
Cell
ClockDR UpdateDR
ShiftDR
To
Next
Cell EXTEST
From Digital Logic
XTAL1/TOSC1 XTAL2/TOSC2
Oscillator
ENABLE OUTPUT
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Scanning the Analog
Comparator
The relevant Comparator signals regarding Boundary-scan are shown in Figure 91. The Bound-
ary-scan cell from Figure 92 is attached to each of these signals. The signals are described in
Table 86.
The Comparator need not be used for pure connectivity testing, since all analog inputs are
shared with a digital port pin as well.
Figure 91. Analog Comparator
Figure 92. General Boundary-scan Cell used for Signals for Comparator
ACBG
BANDGAP
REFERENCE
AC_IDLE
ACO
0
1
DQ DQ
G
0
1
From
Previous
Cell
ClockDR UpdateDR
ShiftDR
To
Next
Cell EXTEST
To Snalog Circuitry/
To Digital Logic
From Digital Logic/
From Analog Ciruitry
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ATmega162
Boundary-scan
Order
Table 87 shows the Scan order between TDI and TDO when the Boundary-scan chain is
selected as data path. Bit 0 is the LSB; the first bit scanned in, and the first bit scanned out. The
scan order follows the pinout order as far as possible. Therefore, the bits of Port A and Port E is
scanned in the opposite bit order of the other ports. Exceptions from the rules are the Scan
chains for the analog circuits, which constitute the most significant bits of the scan chain regard-
less of which physical pin they are connected to. In Figure 87, PXn. Data corresponds to FF0,
PXn. Control corresponds to FF1, and PXn. Pullup_enable corresponds to FF2. Bit 4, 5, 6, and
7of Port C is not in the scan chain, since these pins constitute the TAP pins when the JTAG is
enabled.
Table 86. Boundary-scan Signals for the Analog Comparator
Signal
Name
Direction as
seen from the
Comparator Description
Recommended
Input when Not
in Use
Output Values when
Recommended
Inputs are Used
AC_IDLE input Turns off Analog
comparator
when true
1 Depends upon µC
code being executed
ACO output Analog
Comparator
Output
Will become
input to µC code
being executed
0
ACBG input Bandgap
Reference
enable
0 Depends upon µC
code being executed
Table 87. ATmega162 Boundary-scan Order
Bit Number Signal Name Module
105 AC_IDLE Comparator
104 ACO
103 ACBG
102 PB0.Data Port B
101 PB0.Control
100 PB0.Pullup_Enable
99 PB1.Data
98 PB1.Control
97 PB1.Pullup_Enable
96 PB2.Data
95 PB2.Control
94 PB2.Pullup_Enable
93 PB3.Data
92 PB3.Control
91 PB3.Pullup_Enable
90 PB4.Data
89 PB4.Control
88 PB4.Pullup_Enable
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87 PB5.Data Port B
86 PB5.Control
85 PB5.Pullup_Enable
84 PB6.Data
83 PB6.Control
82 PB6.Pullup_Enable
81 PB7.Data
80 PB7.Control
79 PB7.Pullup_Enable
78 RSTT Reset Logic
(Observe-only)
77 RSTHV
76 TOSC 32 kHz Timer Oscillator
75 TOSCON
74 PD0.Data Port D
73 PD0.Control
72 PD0.Pullup_Enable
71 PD1.Data
70 PD1.Control
69 PD1.Pullup_Enable
68 PD2.Data
67 PD2.Control
66 PD2.Pullup_Enable
65 PD3.Data
64 PD3.Control
63 PD3.Pullup_Enable
62 PD4.Data
61 PD4.Control
60 PD4.Pullup_Enable
59 PD5.Data Port D
58 PD5.Control
57 PD5.Pullup_Enable
56 PD6.Data
55 PD6.Control
54 PD6.Pullup_Enable
53 PD7.Data
52 PD7.Control
Table 87. ATmega162 Boundary-scan Order (Continued)
Bit Number Signal Name Module
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51 PD7.Pullup_Enable Port D
50 EXTCLKEN Enable signals for main
Clock/Oscillators
49 OSCON
48 OSC32EN
47 EXTCLK (XTAL1) Clock input and Oscillators
for the main clock (Observe-
only)
46 OSCCK
45 OSC32CK
44 PC0.Data Port C
43 PC0.Control
42 PC0.Pullup_Enable
41 PC1.Data
40 PC1.Control
39 PC1.Pullup_Enable
38 PC2.Data
37 PC2.Control
36 PC2.Pullup_Enable
35 PC3.Data
34 PC3.Control
33 PC3.Pullup_Enable
32 PE2.Data Port E
31 PE2.Control
30 PE2.Pullup_Enable
29 PE1.Data
28 PE1.Control
27 PE1.Pullup_Enable
26 PE0.Data
25 PE0.Control
24 PE0.Pullup_Enable
23 PA7.Data Port A
22 PA7.Control
21 PA7.Pullup_Enable
20 PA6.Data
19 PA6.Control
18 PA6.Pullup_Enable
17 PA5.Data
16 PA5.Control
Table 87. ATmega162 Boundary-scan Order (Continued)
Bit Number Signal Name Module
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Note: 1. PRIVATE_SIGNAL1 should always be scanned in as zero.
Boundary-scan
Description
Language Files
Boundary-scan Description Language (BSDL) files describe Boundary-scan capable devices in
a standard format used by automated test-generation software. The order and function of bits in
the Boundary-scan Data Register are included in this description. A BSDL file for ATmega162 is
available.
15 PA5.Pullup_Enable Port A
14 PA4.Data
13 PA4.Control
12 PA4.Pullup_Enable
11 PA3.Data
10 PA3.Control
9 PA3.Pullup_Enable
8PA2.Data
7 PA2.Control
6 PA2.Pullup_Enable
5PA1.Data
4 PA1.Control
3 PA1.Pullup_Enable
2PA0.Data
1 PA0.Control
0 PA0.Pullup_Enable
Table 87. ATmega162 Boundary-scan Order (Continued)
Bit Number Signal Name Module
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Boot Loader
Support – Read-
While-Write
Self-
programming
The Boot Loader Support provides a real Read-While-Write Self-programming mechanism for
downloading and uploading program code by the MCU itself. This feature allows flexible applica-
tion software updates controlled by the MCU using a Flash-resident Boot Loader program. The
Boot Loader program can use any available data interface and associated protocol to read code
and write (program) that code into the Flash memory, or read the code from the program mem-
ory. The program code within the Boot Loader section has the capability to write into the entire
Flash, including the Boot Loader memory. The Boot Loader can thus even modify itself, and it
can also erase itself from the code if the feature is not needed anymore. The size of the Boot
Loader memory is configurable with Fuses and the Boot Loader has two separate sets of Boot
Lock bits which can be set independently. This gives the user a unique flexibility to select differ-
ent levels of protection.
Features •Read-While-Write Self-programming
•Flexible Boot Memory Size
•High Security (Separate Boot Lock Bits for a Flexible Protection)
•Separate Fuse to Select Reset Vector
•Optimized Page(1) Size
•Code Efficient Algorithm
•Efficient Read-Modify-Write Support
Note: 1. A page is a section in the Flash consisting of several bytes (see Table 105 on page 236) used
during programming. The page organization does not affect normal operation.
Application and
Boot Loader Flash
Sections
The Flash memory is organized in two main sections, the Application section and the Boot
Loader section (see Figure 94). The size of the different sections is configured by the BOOTSZ
Fuses as shown in Table 93 on page 228 and Figure 94. These two sections can have different
level of protection since they have different sets of Lock bits.
Application Section The Application section is the section of the Flash that is used for storing the application code.
The protection level for the application section can be selected by the Application Boot Lock bits
(Boot Lock bits 0), see Table 89 on page 220. The Application section can never store any Boot
Loader code since the SPM instruction is disabled when executed from the Application section.
BLS – Boot Loader
Section
While the Application section is used for storing the application code, the The Boot Loader soft-
ware must be located in the BLS since the SPM instruction can initiate a programming when
executing from the BLS only. The SPM instruction can access the entire Flash, including the
BLS itself. The protection level for the Boot Loader section can be selected by the Boot Loader
Lock bits (Boot Lock bits 1), see Table 90 on page 220.
Read-While-Write
and No Read-
While-Write Flash
Sections
Whether the CPU supports Read-While-Write or if the CPU is halted during a Boot Loader soft-
ware update is dependent on which address that is being programmed. In addition to the two
sections that are configurable by the BOOTSZ Fuses as described above, the Flash is also
divided into two fixed sections, the Read-While-Write (RWW) section and the No Read-While-
Write (NRWW) section. The limit between the RWW- and NRWW sections is given in Table 94
on page 229 and Figure 94 on page 219. The main difference between the two sections is:
• When erasing or writing a page located inside the RWW section, the NRWW section can be
read during the operation.
• When erasing or writing a page located inside the NRWW section, the CPU is halted during
the entire operation.
Note that the user software can never read any code that is located inside the RWW section dur-
ing a Boot Loader software operation. The syntax “Read-While-Write section” refers to which
section that is being programmed (erased or written), not which section that actually is being
read during a Boot Loader software update.
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RWW – Read-While-
Write Section
If a Boot Loader software update is programming a page inside the RWW section, it is possible
to read code from the Flash, but only code that is located in the NRWW section. During an ongo-
ing programming, the software must ensure that the RWW section never is being read. If the
user software is trying to read code that is located inside the RWW section (i.e., by a
call/jmp/lpm or an interrupt) during programming, the software might end up in an unknown
state. To avoid this, the interrupts should either be disabled or moved to the Boot Loader sec-
tion. The Boot Loader section is always located in the NRWW section. The RWW Section Busy
bit (RWWSB) in the Store Program Memory Control Register (SPMCR) will be read as logical
one as long as the RWW section is blocked for reading. After a programming is completed, the
RWWSB must be cleared by software before reading code located in the RWW section. See
“Store Program Memory Control Register – SPMCR” on page 221. for details on how to clear
RWWSB.
NRWW – No Read-
While-Write Section
The code located in the NRWW section can be read when the Boot Loader software is updating
a page in the RWW section. When the Boot Loader code updates the NRWW section, the CPU
is halted during the entire Page Erase or Page Write operation.
Figure 93. Read-While-Write vs. No Read-While-Write
Table 88. Read-While-Write Features
Which Section does the Z-
pointer Address During the
Programming?
Which Section Can be
Read During
Programming?
Is the CPU
Halted?
Read-While-
Write
Supported?
RWW section NRWW section No Yes
NRWW section None Yes No
Read-While-Write
(RWW) Section
No Read-While-Write
(NRWW) Section
Z-pointer
Addresses RWW
Section
Z-pointer
Addresses NRWW
Section
CPU is Halted
During the Operation
Code Located in
NRWW Section
Can be Read During
the Operation
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Figure 94. Memory Sections(1)
Note: 1. The parameters are given in Table 93 on page 228.
Boot Loader Lock
Bits
If no Boot Loader capability is needed, the entire Flash is available for application code. The
Boot Loader has two separate sets of Boot Lock bits which can be set independently. This gives
the user a unique flexibility to select different levels of protection.
The user can select:
• To protect the entire Flash from a software update by the MCU
• To protect only the Boot Loader Flash section from a software update by the MCU
• To protect only the Application Flash section from a software update by the MCU
• Allow software update in the entire Flash
See Table 89 and Table 90 for further details. The Boot Lock bits can be set in software and in
Serial or Parallel Programming mode, but they can be cleared by a chip erase command only.
The general Write Lock (Lock bit mode 2) does not control the programming of the Flash mem-
0x0000
Flashend
Program Memory
BOOTSZ = '11'
Application Flash Section
Boot Loader Flash Section
Flashend
Program Memory
BOOTSZ = '10'
0x0000
Program Memory
BOOTSZ = '01'
Program Memory
BOOTSZ = '00'
Application Flash Section
Boot Loader Flash Section
0x0000
Flashend
Application Flash Section
Flashend
End RWW
Start NRWW
Application flash Section
Boot Loader Flash Section
Boot Loader Flash Section
End RWW
Start NRWW
End RWW
Start NRWW
0x0000
End RWW, End Application
Start NRWW, Start Boot Loader
Application Flash SectionApplication Flash Section
Application Flash Section
Read-While-Write SectionNo Read-While-Write Section Read-While-Write SectionNo Read-While-Write Section
Read While Write SectionNo Read While Write SectionRead-While-Write SectionNo Read-While-Write Section
End Application
Start Boot Loader
End Application
Start Boot Loader
End Application
Start Boot Loader
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ory by SPM instruction. Similarly, the general Read/Write Lock (Lock bit mode 1) does not
control reading nor writing by LPM/SPM, if it is attempted.
Note: 1. “1” means unprogrammed, “0” means programmed
Note: 1. “1” means unprogrammed, “0” means programmed
Table 89. Boot Lock Bit0 Protection Modes (Application Section)(1)
BLB0 Mode BLB02 BLB01 Protection
111
No restrictions for SPM or LPM accessing the Application
section.
2 1 0 SPM is not allowed to write to the Application section.
300
SPM is not allowed to write to the Application section, and
LPM executing from the Boot Loader section is not
allowed to read from the Application section. If Interrupt
Vectors are placed in the Boot Loader section, interrupts
are disabled while executing from the Application section.
401
LPM executing from the Boot Loader section is not
allowed to read from the Application section. If Interrupt
Vectors are placed in the Boot Loader section, interrupts
are disabled while executing from the Application section.
Table 90. Boot Lock Bit1 Protection Modes (Boot Loader Section)(1)
BLB1 Mode BLB12 BLB11 Protection
111
No restrictions for SPM or LPM accessing the Boot Loader
section.
2 1 0 SPM is not allowed to write to the Boot Loader section.
300
SPM is not allowed to write to the Boot Loader section,
and LPM executing from the Application section is not
allowed to read from the Boot Loader section. If Interrupt
Vectors are placed in the Application section, interrupts
are disabled while executing from the Boot Loader section.
401
LPM executing from the Application section is not allowed
to read from the Boot Loader section. If Interrupt Vectors
are placed in the Application section, interrupts are
disabled while executing from the Boot Loader section.
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Entering the Boot
Loader Program
Entering the Boot Loader takes place by a jump or call from the application program. This may
be initiated by a trigger such as a command received via USART, or SPI interface. Alternatively,
the Boot Reset Fuse can be programmed so that the Reset Vector is pointing to the Boot Flash
start address after a reset. In this case, the Boot Loader is started after a reset. After the applica-
tion code is loaded, the program can start executing the application code. Note that the fuses
cannot be changed by the MCU itself. This means that once the Boot Reset Fuse is pro-
grammed, the Reset Vector will always point to the Boot Loader Reset and the fuse can only be
changed through the Serial or Parallel Programming interface.
Note: 1. “1” means unprogrammed, “0” means programmed
Store Program
Memory Control
Register – SPMCR
The Store Program Memory Control Register contains the control bits needed to control the Boot
Loader operations.
• Bit 7 – SPMIE: SPM Interrupt Enable
When the SPMIE bit is written to one, and the I-bit in the Status Register is set (one), the SPM
ready interrupt will be enabled. The SPM ready Interrupt will be executed as long as the SPMEN
bit in the SPMCR Register is cleared.
• Bit 6 – RWWSB: Read-While-Write Section Busy
When a Self-programming (Page Erase or Page Write) operation to the RWW section is initi-
ated, the RWWSB will be set (one) by hardware. When the RWWSB bit is set, the RWW section
cannot be accessed. The RWWSB bit will be cleared if the RWWSRE bit is written to one after a
Self-programming operation is completed. Alternatively the RWWSB bit will automatically be
cleared if a page load operation is initiated.
• Bit 5 – Res: Reserved Bit
This bit is a reserved bit in the ATmega162 and always read as zero.
• Bit 4 – RWWSRE: Read-While-Write Section Read Enable
When programming (Page Erase or Page Write) to the RWW section, the RWW section is
blocked for reading (the RWWSB will be set by hardware). To re-enable the RWW section, the
user software must wait until the programming is completed (SPMEN will be cleared). Then, if
the RWWSRE bit is written to one at the same time as SPMEN, the next SPM instruction within
four clock cycles re-enables the RWW section. The RWW section cannot be re-enabled while
the Flash is busy with a Page Erase or a Page Write (SPMEN is set). If the RWWSRE bit is writ-
ten while the Flash is being loaded, the Flash load operation will abort and the data loaded will
be lost.
Table 91. Boot Reset Fuse(1)
BOOTRST Reset Address
1 Reset Vector = Application Reset (address 0x0000).
0 Reset Vector = Boot Loader Reset (see Table 93 on page 228).
Bit 765 4 3210
SPMIE RWWSB – RWWSRE BLBSET PGWRT PGERS SPMEN SPMCR
Read/Write R/W R R R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
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• Bit 3 – BLBSET: Boot Lock Bit Set
If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock
cycles sets Boot Lock bits, according to the data in R0. The data in R1 and the address in the Z-
pointer are ignored. The BLBSET bit will automatically be cleared upon completion of the Lock
bit set, or if no SPM instruction is executed within four clock cycles.
An LPM instruction within three cycles after BLBSET and SPMEN are set in the SPMCR Regis-
ter, will read either the Lock bits or the Fuse bits (depending on Z0 in the Z-pointer) into the
destination register. See “Reading the Fuse and Lock Bits from Software” on page 225 for
details.
• Bit 2 – PGWRT: Page Write
If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock
cycles executes Page Write, with the data stored in the temporary buffer. The page address is
taken from the high part of the Z-pointer. The data in R1 and R0 are ignored. The PGWRT bit
will auto–clear upon completion of a Page Write, or if no SPM instruction is executed within four
clock cycles. The CPU is halted during the entire Page Write operation if the NRWW section is
addressed.
• Bit 1 – PGERS: Page Erase
If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock
cycles executes Page Erase. The page address is taken from the high part of the Z-pointer. The
data in R1 and R0 are ignored. The PGERS bit will auto-clear upon completion of a Page Erase,
or if no SPM instruction is executed within four clock cycles. The CPU is halted during the entire
Page Write operation if the NRWW section is addressed.
• Bit 0 – SPMEN: Store Program Memory Enable
This bit enables the SPM instruction for the next four clock cycles. If written to one together with
either RWWSRE, BLBSET, PGWRT’ or PGERS, the following SPM instruction will have a spe-
cial meaning, see description above. If only SPMEN is written, the following SPM instruction will
store the value in R1:R0 in the temporary page buffer addressed by the Z-pointer. The LSB of
the Z-pointer is ignored. The SPMEN bit will auto-clear upon completion of an SPM instruction,
or if no SPM instruction is executed within four clock cycles. During Page Erase and Page Write,
the SPMEN bit remains high until the operation is completed.
Writing any other combination than “10001”, “01001”, “00101”, “00011” or “00001” in the lower
five bits will have no effect.
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Addressing the
Flash During Self-
programming
The Z-pointer is used to address the SPM commands.
Since the Flash is organized in pages (see Table 105 on page 236), the Program Counter can
be treated as having two different sections. One section, consisting of the least significant bits, is
addressing the words within a page, while the most significant bits are addressing the pages.
This is shown in Figure 95. Note that the Page Erase and Page Write operations are addressed
independently. Therefore it is of major importance that the Boot Loader software addresses the
same page in both the Page Erase and Page Write operation. Once a programming operation is
initiated, the address is latched and the Z-pointer can be used for other operations.
The only SPM operation that does not use the Z-pointer is Setting the Boot Loader Lock bits.
The content of the Z-pointer is ignored and will have no effect on the operation. The LPM
instruction does also use the Z-pointer to store the address. Since this instruction addresses the
Flash byte-by-byte, also the LSB (bit Z0) of the Z-pointer is used.
Figure 95. Addressing the Flash during SPM(1)
Notes: 1. The different variables used in Figure 95 are listed in Table 95 on page 230.
2. PCPAGE and PCWORD are listed in Table 105 on page 236.
Bit 151413121110 9 8
ZH (R31) Z15 Z14 Z13 Z12 Z11 Z10 Z9 Z8
ZL (R30) Z7Z6Z5Z4Z3Z2Z1Z0
76543210
PROGRAM MEMORY
0115
Z - REGISTER
BIT
0
ZPAGEMSB
WORD ADDRESS
WITHIN A PAGE
PAGE ADDRESS
WITHIN THE FLASH
ZPCMSB
INSTRUCTION WORD
PAGE PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
PAGE
PCWORDPCPAGE
PCMSB PAGEMSB
PROGRAM
COUNTER
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Self-programming
the Flash
The program memory is updated in a page by page fashion. Before programming a page with
the data stored in the temporary page buffer, the page must be erased. The temporary page buf-
fer is filled one word at a time using SPM and the buffer can be filled either before the Page
Erase command or between a Page Erase and a Page Write operation:
Alternative 1, fill the buffer before a Page Erase
• Fill temporary page buffer
• Perform a Page Erase
• Perform a Page Write
Alternative 2, fill the buffer after Page Erase
• Perform a Page Erase
• Fill temporary page buffer
• Perform a Page Write
If only a part of the page needs to be changed, the rest of the page must be stored (for example
in the temporary page buffer) before the erase, and then be rewritten. When using alternative 1,
the Boot Loader provides an effective Read-Modify-Write feature which allows the user software
to first read the page, do the necessary changes, and then write back the modified data. If alter-
native 2 is used, it is not possible to read the old data while loading since the page is already
erased. The temporary page buffer can be accessed in a random sequence. It is essential that
the page address used in both the Page Erase and Page Write operation is addressing the same
page. See “Simple Assembly Code Example for a Boot Loader” on page 227 for an assembly
code example.
Performing Page
Erase by SPM
To execute Page Erase, set up the address in the Z-pointer, write “X0000011” to SPMCR and
execute SPM within four clock cycles after writing SPMCR. The data in R1 and R0 is ignored.
The page address must be written to PCPAGE in the Z-register. Other bits in the Z-pointer will
be ignored during this operation.
• Page Erase to the RWW section: The NRWW section can be read during the Page Erase.
• Page Erase to the NRWW section: The CPU is halted during the operation.
Filling the Temporary
Buffer (Page Loading)
To write an instruction word, set up the address in the Z-pointer and data in R1:R0, write
“00000001” to SPMCR and execute SPM within four clock cycles after writing SPMCR. The con-
tent of PCWORD in the Z-register is used to address the data in the temporary buffer. The
temporary buffer will auto-erase after a Page Write operation or by writing the RWWSRE bit in
SPMCR. It is also erased after a System Reset. Note that it is not possible to write more than
one time to each address without erasing the temporary buffer.
Note: If the EEPROM is written in the middle of an SPM Page Load operation, all data loaded will be
lost.
Performing a Page
Write
To execute Page Write, set up the address in the Z-pointer, write “X0000101” to SPMCR and
execute SPM within four clock cycles after writing SPMCR. The data in R1 and R0 is ignored.
The page address must be written to PCPAGE. Other bits in the Z-pointer must be written zero
during this operation.
• Page Write to the RWW section: The NRWW section can be read during the Page Write.
• Page Write to the NRWW section: The CPU is halted during the operation.
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Using the SPM
Interrupt
If the SPM interrupt is enabled, the SPM interrupt will generate a constant interrupt when the
SPMEN bit in SPMCR is cleared. This means that the interrupt can be used instead of polling
the SPMCR Register in software. When using the SPM interrupt, the Interrupt Vectors should be
moved to the BLS section to avoid that an interrupt is accessing the RWW section when it is
blocked for reading. How to move the interrupts is described in “Interrupts” on page 57.
Consideration while
Updating BLS
Special care must be taken if the user allows the Boot Loader section to be updated by leaving
Boot Lock bit11 unprogrammed. An accidental write to the Boot Loader itself can corrupt the
entire Boot Loader, and further software updates might be impossible. If it is not necessary to
change the Boot Loader software itself, it is recommended to program the Boot Lock bit11 to
protect the Boot Loader software from any internal software changes.
Prevent Reading the
RWW Section During
Self-programming
During Self-programming (either Page Erase or Page Write), the RWW section is always
blocked for reading. The user software itself must prevent that this section is addressed during
the self programming operation. The RWWSB in the SPMCR will be set as long as the RWW
section is busy. During Self-programming the Interrupt Vector table should be moved to the BLS
as described in “Interrupts” on page 57, or the interrupts must be disabled. Before addressing
the RWW section after the programming is completed, the user software must clear the
RWWSB by writing the RWWSRE. See “Simple Assembly Code Example for a Boot Loader” on
page 227 for an example.
Setting the Boot
Loader Lock Bits by
SPM
To set the Boot Loader Lock bits, write the desired data to R0, write “X0001001” to SPMCR and
execute SPM within four clock cycles after writing SPMCR. The only accessible Lock bits are the
Boot Lock bits that may prevent the Application and Boot Loader section from any software
update by the MCU.
See Table 89 and Table 90 for how the different settings of the Boot Loader bits affect the Flash
access.
If bits 5..2 in R0 are cleared (zero), the corresponding Boot Lock bit will be programmed if an
SPM instruction is executed within four cycles after BLBSET and SPMEN are set in SPMCR.
The Z-pointer is don’t care during this operation, but for future compatibility it is recommended to
load the Z-pointer with 0x0001 (same as used for reading the Lock bits). For future compatibility
it is also recommended to set bits 7, 6, 1, and 0 in R0 to “1” when writing the Lock bits. When
programming the Lock bits the entire Flash can be read during the operation.
EEPROM Write
Prevents Writing to
SPMCR
Note that an EEPROM write operation will block all software programming to Flash. Reading the
Fuses and Lock bits from software will also be prevented during the EEPROM write operation. It
is recommended that the user checks the status bit (EEWE) in the EECR Register and verifies
that the bit is cleared before writing to the SPMCR Register.
Reading the Fuse and
Lock Bits from
Software
It is possible to read both the Fuse and Lock bits from software. To read the Lock bits, load the
Z-pointer with 0x0001 and set the BLBSET and SPMEN bits in SPMCR. When an LPM instruc-
tion is executed within three CPU cycles after the BLBSET and SPMEN bits are set in SPMCR,
the value of the Lock bits will be loaded in the destination register. The BLBSET and SPMEN
bits will auto-clear upon completion of reading the Lock bits or if no LPM instruction is executed
within three CPU cycles or no SPM instruction is executed within four CPU cycles. When BLB-
SET and SPMEN are cleared, LPM will work as described in the Instruction set Manual.
Bit 76543210
R0 1 1 BLB12 BLB11 BLB02 BLB01 1 1
Bit 76543210
Rd – – BLB12 BLB11 BLB02 BLB01 LB2 LB1
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The algorithm for reading the Fuse Low byte is similar to the one described above for reading
the Lock bits. To read the Fuse Low byte, load the Z-pointer with 0x0000 and set the BLBSET
and SPMEN bits in SPMCR. When an LPM instruction is executed within three cycles after the
BLBSET and SPMEN bits are set in the SPMCR, the value of the Fuse Low byte (FLB) will be
loaded in the destination register as shown below. Refer to Table 100 on page 233 for a detailed
description and mapping of the Fuse Low byte.
Similarly, when reading the Fuse High byte, load 0x0003 in the Z-pointer. When an LPM instruc-
tion is executed within three cycles after the BLBSET and SPMEN bits are set in the SPMCR,
the value of the Fuse High byte (FHB) will be loaded in the destination register as shown below.
Refer to Table 98 on page 232 for detailed description and mapping of the Fuse High byte.
When reading the Extended Fuse byte, load 0x0002 in the Z-pointer. When an LPM instruction
is executed within three cycles after the BLBSET and SPMEN bits are set in the SPMCR, the
value of the Extended Fuse byte (EFB) will be loaded in the destination register as shown below.
Refer to Table 98 on page 232 for detailed description and mapping of the Extended Fuse byte.
Fuse and Lock bits that are programmed, will be read as zero. Fuse and Lock bits that are
unprogrammed, will be read as one.
Preventing Flash
Corruption
During periods of low VCC, the Flash program can be corrupted because the supply voltage is
too low for the CPU and the Flash to operate properly. These issues are the same as for board
level systems using the Flash, and the same design solutions should be applied.
A Flash program corruption can be caused by two situations when the voltage is too low. First, a
regular write sequence to the Flash requires a minimum voltage to operate correctly. Secondly,
the CPU itself can execute instructions incorrectly, if the supply voltage for executing instructions
is too low.
Flash corruption can easily be avoided by following these design recommendations (one is
sufficient):
1. If there is no need for a Boot Loader update in the system, program the Boot Loader Lock
bits to prevent any Boot Loader software updates.
2. Keep the AVR RESET active (low) during periods of insufficient power supply voltage.
This can be done by enabling the internal Brown-out Detector (BOD) if the operating volt-
age matches the detection level. If not, an external low VCC Reset Protection circuit can
be used. If a Reset occurs while a write operation is in progress, the write operation will
be completed provided that the power supply voltage is sufficient.
3. Keep the AVR core in Power-down sleep mode during periods of low VCC. This will pre-
vent the CPU from attempting to decode and execute instructions, effectively protecting
the SPMCR Register and thus the Flash from unintentional writes.
Bit 76543210
Rd FLB7 FLB6 FLB5 FLB4 FLB3 FLB2 FLB1 FLB0
Bit 76543210
Rd FHB7 FHB6 FHB5 FHB4 FHB3 FHB2 FHB1 FHB0
Bit 76543210
Rd – – – EFB4 EFB3 EFB2 EFB1 –
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Programming Time for
Flash When Using
SPM
The calibrated RC Oscillator is used to time Flash accesses. Table 92 shows the typical pro-
gramming time for Flash accesses from the CPU.
Simple Assembly
Code Example for a
Boot Loader
;-the routine writes one?page of data from RAM to Flash
; the first data locatio? in RAM is pointed to by the Y pointer
; the first data locatio? in Flash is pointed to by the Z-pointer
;-error handling is not ?ncluded
;-the routine must be pl?ced inside the boot space
; (at least the Do_spm s?b routine). Only code inside NRWW section can
; be read during self-pr?gramming (page erase and page write).
;-registers used: r0, r1? temp1 (r16), temp2 (r17), looplo (r24),
; loophi (r25), spmcrval?(r20)
; storing and restoring ?f registers is not included in the routine
; register usage can be ?ptimized at the expense of code size
;-It is assumed that eit?er the interrupt table is moved to the Boot
; loader section or that?the interrupts are disabled.
.equ PAGESIZEB = PAGESIZE*2 ;PAGESIZEB is page size in BYTES, not
; words
.org SMALLBOOTSTART
Write_page:
; page erase
ldi spmcrval, (1<<PGERS) | (1<<SPMEN)
call Do_spm
; re-enable the RWW section
ldi spmcrval, (1<<RWWSRE) | (1<<SPMEN)
call Do_spm
; transfer data from RAM to Flash page buffer
ldi looplo, low(PAGESIZEB) ;init loop variable
ldi loophi, high(PAGESIZEB) ;not required for PAGESIZEB<=256
Wrloop:
ld r0, Y+
ld r1, Y+
ldi spmcrval, (1<<SPMEN)
call Do_spm
adiw ZH:ZL, 2
sbiw loophi:looplo, 2 ;use subi for PAGESIZEB<=256
brne Wrloop
; execute page write
subi ZL, low(PAGESIZEB) ;restore pointer
sbci ZH, high(PAGESIZEB) ;not required for PAGESIZEB<=256
ldi spmcrval, (1<<PGWRT) | (1<<SPMEN)
call Do_spm
; re-enable the RWW section
ldi spmcrval, (1<<RWWSRE) | (1<<SPMEN)
call Do_spm
; read back and check, optional
ldi looplo, low(PAGESIZEB) ;init loop variable
ldi loophi, high(PAGESIZEB) ;not required for PAGESIZEB<=256
subi YL, low(PAGESIZEB) ;restore pointer
sbci YH, high(PAGESIZEB)
Rdloop:
lpm r0, Z+
Table 92. SPM Programming Time
Symbol Min Programming Time Max Programming Time
Flash Write (Page Erase, Page Write,
and Write Lock bits by SPM) 3.7ms 4.5ms
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ld r1, Y+
cpse r0, r1
jmp Error
sbiw loophi:looplo, 1 ;use subi for PAGESIZEB<=256
brne Rdloop
; return to RWW section
; verify that RWW section is safe to read
Return:
in temp1, SPMCR
sbrs temp1, RWWSB ; If RWWSB is set, the RWW section is not
; ready yet
ret
; re-enable the RWW section
ldi spmcrval, (1<<RWWSRE) | (1<<SPMEN)
call Do_spm
rjmp Return
Do_spm:
; check for previous SPM complete
Wait_spm:
in temp1, SPMCR
sbrc temp1, SPMEN
rjmp Wait_spm
; input: spmcrval determines SPM action
; disable interrupts if enabled, store status
in temp2, SREG
cli
; check that no EEPROM write access is present
Wait_ee:
sbic EECR, EEWE
rjmp Wait_ee
; SPM timed sequence
out SPMCR, spmcrval
spm
; restore SREG (to enable interrupts if originally enabled)
out SREG, temp2
ret
ATmega162 Boot
Loader Parameters
In Table 93 through Table 95, the parameters used in the description of the self programming
are given.
Table 93. Boot Size Configuration(1)
BOOTSZ1 BOOTSZ0
Boot
Size Pages
Application
Flash
Section
Boot
Loader
Flash
Section
End
Application
Section
Boot Reset
Address
(Start Boot
Loader
Section)
11
128
words 20x0000 -
0x1F7F
0x1F80 -
0x1FFF 0x1F7F 0x1F80
10
256
words 40x0000 -
0x1EFF
0x1F00 -
0x1FFF 0x1EFF 0x1F00
01
512
words 80x0000 -
0x1DFF
0x1E00 -
0x1FFF 0x1DFF 0x1E00
00
1024
words 16 0x0000 -
0x1BFF
0x1C00 -
0x1FFF 0x1BFF 0x1C00
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Note: 1. The different BOOTSZ Fuse configurations are shown in Figure 94
Note: 1. For details about these two section, see “NRWW – No Read-While-Write Section” on page
218 and “RWW – Read-While-Write Section” on page 218
Table 94. Read-While-Write Limit
Section Pages Address
Read-While-Write section (RWW) 112 0x0000 - 0x1BFF
No Read-While-Write section (NRWW) 16 0x1C00 - 0x1FFF
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Note: 1. Z15:Z14: always ignored
Z0: should be zero for all SPM commands, byte select for the LPM instruction.
See “Addressing the Flash During Self-programming” on page 223 for details about the use of
Z-pointer during Self-programming.
Table 95. Explanation of Different Variables Used in Figure 95 and the Mapping to the Z-
pointer(1)
Variable
Corresponding
Z-value Description
PCMSB 12 Most significant bit in the Program Counter.
(The Program Counter is 13 bits PC[12:0])
PAG E M S B
5 Most significant bit which is used to address
the words within one page (64 words in a page
requires 6 bits PC [5:0]).
ZPCMSB
Z13 Bit in Z-register that is mapped to PCMSB.
Because Z0 is not used, the ZPCMSB equals
PCMSB + 1.
ZPAGEMSB
Z6 Bit in Z-register that is mapped to PCMSB.
Because Z0 is not used, the ZPAGEMSB
equals PAGEMSB + 1.
PCPAGE PC[12:6] Z13:Z7 Program Counter page address: Page select,
for Page Erase and Page Write
PCWORD
PC[5:0] Z6:Z1 Program Counter word address: Word select,
for filling temporary buffer (must be zero during
Page Write operation)
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Memory
Programming
Program And Data
Memory Lock Bits
The ATmega162 provides six Lock bits which can be left unprogrammed (“1”) or can be pro-
grammed (“0”) to obtain the additional features listed in Table 97. The Lock bits can only be
erased to “1” with the Chip Erase command.
Note: 1. “1” means unprogrammed, “0” means programmed
Table 96. Lock Bit Byte(1)
Lock Bit Byte Bit no Description Default Value
7 – 1 (unprogrammed)
6 – 1 (unprogrammed)
BLB12 5 Boot Lock bit 1 (unprogrammed)
BLB11 4 Boot Lock bit 1 (unprogrammed)
BLB02 3 Boot Lock bit 1 (unprogrammed)
BLB01 2 Boot Lock bit 1 (unprogrammed)
LB2 1 Lock bit 1 (unprogrammed)
LB1 0 Lock bit 1 (unprogrammed)
Table 97. Lock Bit Protection Modes(1)(2)
Memory Lock Bits Protection Type
LB Mode LB2 LB1
1 1 1 No memory lock features enabled.
210
Further programming of the Flash and EEPROM is
disabled in Parallel and SPI/JTAG Serial Programming
mode. The Fuse bits are locked in both Serial and Parallel
Programming mode(1).
300
Further programming and verification of the Flash and
EEPROM is disabled in Parallel and SPI/JTAG Serial
Programming mode. Also the Boot Lock bits and the Fuse
bits are locked in both Serial and Parallel Programming
mode(1).
BLB0 Mode BLB02 BLB01
111
No restrictions for SPM or LPM accessing the Application
section.
2 1 0 SPM is not allowed to write to the Application section.
300
SPM is not allowed to write to the Application section, and
LPM executing from the Boot Loader section is not
allowed to read from the Application section. If Interrupt
Vectors are placed in the Boot Loader section, interrupts
are disabled while executing from the Application section.
401
LPM executing from the Boot Loader section is not
allowed to read from the Application section. If Interrupt
Vectors are placed in the Boot Loader section, interrupts
are disabled while executing from the Application section.
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Notes: 1. Program the Fuse bits and Boot Lock bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed
Fuse Bits The ATmega162 has three Fuse bytes. Table 99 and Table 100 describe briefly the functionality
of all the fuses and how they are mapped into the Fuse bytes. Note that the fuses are read as
logical zero, “0”, if they are programmed.
Notes: 1. See “ATmega161 Compatibility Mode” on page 4 for details.
2. See Table 19 on page 50 for BODLEVEL Fuse decoding.
BLB1 Mode BLB12 BLB11
111
No restrictions for SPM or LPM accessing the Boot Loader
section.
2 1 0 SPM is not allowed to write to the Boot Loader section.
300
SPM is not allowed to write to the Boot Loader section,
and LPM executing from the Application section is not
allowed to read from the Boot Loader section. If Interrupt
Vectors are placed in the Application section, interrupts
are disabled while executing from the Boot Loader section.
401
LPM executing from the Application section is not allowed
to read from the Boot Loader section. If Interrupt Vectors
are placed in the Application section, interrupts are
disabled while executing from the Boot Loader section.
Table 97. Lock Bit Protection Modes(1)(2) (Continued)
Memory Lock Bits Protection Type
Table 98. Extended Fuse Byte(1)(2)
Fuse Low Byte Bit no Description Default Value
–7– 1
–6– 1
–5– 1
M161C 4 ATmega161 compatibility
mode 1 (unprogrammed)
BODLEVEL2(2) 3Brown-out Detector
trigger level 1 (unprogrammed)
BODLEVEL1(2) 2Brown-out Detector
trigger level 1 (unprogrammed)
BODLEVEL0(2) 1Brown-out Detector
trigger level 1 (unprogrammed)
–0– 1
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Notes: 1. The SPIEN Fuse is not accessible in SPI Serial Programming mode.
2. The default value of BOOTSZ1:0 results in maximum Boot Size. See Table 93 on page 228 for
details.
3. Never ship a product with the OCDEN Fuse programmed regardless of the setting of Lock bits
and the JTAGEN Fuse. A programmed OCDEN Fuse enables some parts of the clock system
to be running in all sleep modes. This may increase the power consumption.
4. If the JTAG interface is left unconnected, the JTAGEN fuse should if possible be disabled. This
to avoid static current at the TDO pin in the JTAG interface.
Notes: 1. The default value of SUT1:0 results in maximum start-up time for the default clock source. See
Table 12 on page 39 for details.
2. The default setting of CKSEL3:0 results in Internal RC Oscillator @ 8 MHz. See Table 5 on
page 36 for details.
3. The CKOUT Fuse allow the system clock to be output on PortB 0. See “Clock output buffer” on
page 40 for details.
4. See “System Clock Prescaler” on page 41 for details.
The status of the Fuse bits is not affected by Chip Erase. Note that the Fuse bits are locked if
Lock bit1 (LB1) is programmed. Program the Fuse bits before programming the Lock bits.
Table 99. Fuse High Byte
Fuse Low Byte Bit no Description Default Value
OCDEN(3) 7 Enable OCD 1 (unprogrammed, OCD
disabled)
JTAGEN(4) 6 Enable JTAG 0 (programmed, JTAG
enabled)
SPIEN(1) 5Enable Serial Program and Data
Downloading
0 (programmed, SPI prog.
enabled)
WDTON 4 Watchdog Timer always on 1 (unprogrammed)
EESAVE 3 EEPROM memory is preserved
through the Chip Erase
1 (unprogrammed,
EEPROM not preserved)
BOOTSZ1 2 Select Boot Size (see Table 93 for
details) 0 (programmed)(2)
BOOTSZ0 1 Select Boot Size (see Table 93 for
details) 0 (programmed)(2)
BOOTRST 0 Select Reset Vector 1 (unprogrammed)
Table 100. Fuse Low Byte
Fuse Low Byte Bit no Description Default value
CKDIV8(4) 7 Divide clock by 8 0 (programmed)
CKOUT(3) 6 Clock Output 1 (unprogrammed)
SUT1 5 Select start-up time 1 (unprogrammed)(1)
SUT0 4 Select start-up time 0 (programmed)(1)
CKSEL3 3 Select Clock source 0 (programmed)(2)
CKSEL2 2 Select Clock source 0 (programmed)(2)
CKSEL1 1 Select Clock source 1 (unprogrammed)(2)
CKSEL0 0 Select Clock source 0 (programmed)(2)
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Latching of Fuses The Fuse values are latched when the device enters Programming mode and changes of the
Fuse values will have no effect until the part leaves Programming mode. This does not apply to
the EESAVE Fuse which will take effect once it is programmed. The Fuses are also latched on
Power-up in Normal mode.
Signature Bytes All Atmel microcontrollers have a 3-byte signature code which identifies the device. This code
can be read in both Serial and Parallel mode, also when the device is locked. The three bytes
reside in a separate address space.
For the ATmega162 the signature bytes are:
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x94 (indicates 16KB Flash memory).
3. 0x002: 0x04 (indicates ATmega162 device when 0x001 is 0x94).
Calibration Byte The ATmega162 has a one-byte calibration value for the internal RC Oscillator. This byte
resides in the high byte of address 0x000 in the signature address space. During Reset, this
byte is automatically written into the OSCCAL Register to ensure correct frequency of the cali-
brated RC Oscillator.
Parallel
Programming
Parameters, Pin
Mapping, and
Commands
This section describes how to parallel program and verify Flash Program memory, EEPROM
Data memory, Memory Lock bits, and Fuse bits in the ATmega162. Pulses are assumed to be at
least 250 ns unless otherwise noted.
Signal Names In this section, some pins of the ATmega162 are referenced by signal names describing their
functionality during parallel programming, see Figure 96 and Table 101. Pins not described in
the following table are referenced by pin names.
The XA1/XA0 pins determine the action executed when the XTAL1 pin is given a positive pulse.
The bit coding is shown in Table 103.
When pulsing WR or OE, the command loaded determines the action executed. The different
Commands are shown in Table 104.
Figure 96. Parallel Programming
VCC
+5V
GND
XTAL1
PD1
PD2
PD3
PD4
PD5
PD6
PB7 - PB0 DATA
RESET
PD7
+12 V
BS1
XA0
XA1
OE
RDY/BSY
PAGEL
PA0
WR
BS2
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Table 101. Pin Name Mapping
Signal Name in
Programming Mode Pin Name I/O Function
RDY/BSY PD1 O 0: Device is busy programming, 1: Device is ready
for new command
OE PD2 I Output Enable (Active low)
WR PD3 I Write Pulse (Active low)
BS1 PD4 I Byte Select 1 (“0” selects low byte, “1” selects high
byte)
XA0 PD5 I XTAL Action Bit 0
XA1 PD6 I XTAL Action Bit 1
PAGEL PD7 I Program Memory and EEPROM data Page Load
BS2 PA0 I Byte Select 2 (“0” selects low byte, “1” selects 2’nd
high byte)
DATA PB7 - 0 I/O Bi-directional Data bus (Output when OE is low)
Table 102. Pin Values used to Enter Programming Mode
Pin Symbol Value
PAGEL Prog_enable[3] 0
XA1 Prog_enable[2] 0
XA0 Prog_enable[1] 0
BS1 Prog_enable[0] 0
Table 103. XA1 and XA0 Coding
XA1 XA0 Action when XTAL1 is Pulsed
0 0 Load Flash or EEPROM address (High or low address byte determined by BS1)
0 1 Load Data (High or Low data byte for Flash determined by BS1).
1 0 Load Command
1 1 No Action, Idle
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Parallel
Programming
Enter Programming
Mode
The following algorithm puts the device in Parallel Programming mode:
1. Apply 4.5 - 5.5V between VCC and GND, and wait at least 100 µs.
2. Set RESET to “0” and toggle XTAL1 at least six times.
3. Set the Prog_enable pins listed in Table 102 on page 235 to “0000” and wait at least 100
ns.
4. Apply 11.5 - 12.5V to RESET. Any activity on Prog_enable pins within 100 ns after +12V
has been applied to RESET
, will cause the device to fail entering Programming mode.
Considerations for
Efficient Programming
The loaded command and address are retained in the device during programming. For efficient
programming, the following should be considered.
• The command needs only be loaded once when writing or reading multiple memory
locations.
• Skip writing the data value 0xFF, that is the contents of the entire EEPROM (unless the
EESAVE Fuse is programmed) and Flash after a Chip Erase.
• Address high byte needs only be loaded before programming or reading a new 256-word
window in Flash or 256 byte EEPROM. This consideration also applies to Signature bytes
reading.
Table 104. Command Byte Bit Coding
Command Byte Command Executed
1000 0000 Chip Erase
0100 0000 Write Fuse Bits
0010 0000 Write Lock Bits
0001 0000 Write Flash
0001 0001 Write EEPROM
0000 1000 Read Signature Bytes and Calibration byte
0000 0100 Read Fuse and Lock Bits
0000 0010 Read Flash
0000 0011 Read EEPROM
Table 105. No. of Words in a Page and no. of Pages in the Flash
Flash Size Page Size PCWORD No. of Pages PCPAGE PCMSB
8K words (16K bytes) 64 words PC[5:0] 128 PC[12:6] 12
Table 106. No. of Words in a Page and no. of Pages in the EEPROM
EEPROM Size Page Size PCWORD No. of pages PCPAGE EEAMSB
512 bytes 4 bytes EEA[1:0] 128 EEA[8:2] 8
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Chip Erase The Chip Erase will erase the Flash and EEPROM(1) memories plus Lock bits. The Lock bits are
not reset until the program memory has been completely erased. The Fuse bits are not
changed. A Chip Erase must be performed before the Flash or EEPROM are reprogrammed.
Note: 1. The EEPRPOM memory is preserved during chip erase if the EESAVE Fuse is programmed.
Load Command “Chip Erase”
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “1000 0000”. This is the command for Chip Erase.
4. Give XTAL1 a positive pulse. This loads the command.
5. Give WR a negative pulse. This starts the Chip Erase. RDY/BSY goes low.
6. Wait until RDY/BSY goes high before loading a new command.
Programming the
Flash
The Flash is organized in pages, see Table 105 on page 236. When programming the Flash, the
program data is latched into a page buffer. This allows one page of program data to be pro-
grammed simultaneously. The following procedure describes how to program the entire Flash
memory:
A. Load Command “Write Flash”
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “0001 0000”. This is the command for Write Flash.
4. Give XTAL1 a positive pulse. This loads the command.
B. Load Address Low byte
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS1 to “0”. This selects low address.
3. Set DATA = Address low byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address low byte.
C. Load Data Low Byte
1. Set XA1, XA0 to “01”. This enables data loading.
2. Set DATA = Data low byte (0x00 - 0xFF).
3. Give XTAL1 a positive pulse. This loads the data byte.
D. Load Data High Byte
1. Set BS1 to “1”. This selects high data byte.
2. Set XA1, XA0 to “01”. This enables data loading.
3. Set DATA = Data high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the data byte.
E. Latch Data
1. Set BS1 to “1”. This selects high data byte.
2. Give PAGEL a positive pulse. This latches the data bytes (See Figure 98 for signal
waveforms).
F. Repeat B through E until the entire buffer is filled or until all data within the page is loaded.
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While the lower bits in the address are mapped to words within the page, the higher bits address
the pages within the FLASH. This is illustrated in Figure 97 on page 238. Note that if less than
eight bits are required to address words in the page (pagesize < 256), the most significant bit(s)
in the address low byte are used to address the page when performing a Page Write.
G. Load Address High byte
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS1 to “1”. This selects high address.
3. Set DATA = Address high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address high byte.
H. Program Page
1. Give WR a negative pulse. This starts programming of the entire page of data. RDY/BSY
goes low.
2. Wait until RDY/BSY goes high. (See Figure 98 for signal waveforms)
I. Repeat B through H until the entire Flash is programmed or until all data has been
programmed.
J. End Page Programming
1. 1. Set XA1, XA0 to “10”. This enables command loading.
2. Set DATA to “0000 0000”. This is the command for No Operation.
3. Give XTAL1 a positive pulse. This loads the command, and the internal write signals are
reset.
Figure 97. Addressing the Flash which is Organized in Pages(1)
Note: 1. PCPAGE and PCWORD are listed in Table 105 on page 236.
PROGRAM MEMORY
WORD ADDRESS
WITHIN A PAGE
PAGE ADDRESS
WITHIN THE FLASH
INSTRUCTION WORD
PAGE PCWORD[PAGEMSB:0]:
00
01
02
PAGEEND
PAGE
PCWORDPCPAGE
PCMSB PAGEMSB
PROGRAM
COUNTER
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Figure 98. Programming the Flash Waveforms
Note: “XX” is don’t care. The letters refer to the programming description above.
Programming the
EEPROM
The EEPROM is organized in pages, see Table 106 on page 236. When programming the
EEPROM, the program data is latched into a page buffer. This allows one page of data to be
programmed simultaneously. The programming algorithm for the EEPROM data memory is as
follows (refer to “Programming the Flash” on page 237 for details on Command, Address and
Data loading):
1. A: Load Command “0001 0001”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. C: Load Data (0x00 - 0xFF).
5. E: Latch data (give PAGEL a positive pulse).
K: Repeat 3 through 5 until the entire buffer is filled.
L: Program EEPROM page
1. Set BS to “0”.
2. Give WR a negative pulse. This starts programming of the EEPROM page. RDY/BSY
goes low.
3. Wait until to RDY/BSY goes high before programming the next page
(See Figure 99 for signal waveforms).
RDY/BSY
WR
OE
RESET +12V
PAGEL
BS2
0x10 ADDR. LOW ADDR. HIGH
DATA DATA LOW DATA HIGH ADDR. LOW DATA LOW DATA HIGH
XA1
XA0
BS1
XTAL1
XX XX XX
ABCDEBCDEGH
F
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Figure 99. Programming the EEPROM Waveforms
Reading the Flash The algorithm for reading the Flash memory is as follows (refer to “Programming the Flash” on
page 237 for details on Command and Address loading):
1. A: Load Command “0000 0010”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. Set OE to “0”, and BS1 to “0”. The Flash word low byte can now be read at DATA.
5. Set BS to “1”. The Flash word high byte can now be read at DATA.
6. Set OE to “1”.
Reading the EEPROM The algorithm for reading the EEPROM memory is as follows (refer to “Programming the Flash”
on page 237 for details on Command and Address loading):
1. A: Load Command “0000 0011”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. Set OE to “0”, and BS1 to “0”. The EEPROM Data byte can now be read at DATA.
5. Set OE to “1”.
Programming the
Fuse Low Bits
The algorithm for programming the Fuse Low bits is as follows (refer to “Programming the Flash”
on page 237 for details on Command and Data loading):
1. A: Load Command “0100 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. Set BS1 to “0” and BS2 to “0”. This selects low data byte.
4. Give WR a negative pulse and wait for RDY/BSY to go high.
RDY/BSY
WR
OE
RESET +12V
PAGEL
BS2
0x11 ADDR. HIGH
DATA ADDR. LOW DATA ADDR. LOW DATA XX
XA1
XA0
BS1
XTAL1
XX
AGBCEB C EL
K
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Programming the
Fuse High Bits
The algorithm for programming the Fuse high bits is as follows (refer to “Programming the Flash”
on page 237 for details on Command and Data loading):
1. A: Load Command “0100 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. Set BS1 to “1” and BS2 to “0”. This selects high data byte.
4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. Set BS1 to “0”. This selects low data byte.
Programming the
Extended Fuse Bits
The algorithm for programming the Extended Fuse bits is as follows (refer to “Programming the
Flash” on page 237 for details on Command and Data loading):
1. 1. A: Load Command “0100 0000”.
2. 2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. 3. Set BS1 to “0” and BS2 to “1”. This selects extended data byte.
4. 4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. 5. Set BS2 to “0”. This selects low data byte.
Figure 100. Programming the FUSES Waveforms
RDY/BSY
WR
OE
RESET +12V
PAGEL
0x40
DATA DATA XX
XA1
XA0
BS1
XTAL1
AC
0x40 DATA XX
AC
Write Fuse Low byte Write Fuse high byte
0x40 DATA XX
AC
Write Extended Fuse byte
BS2
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Programming the Lock
Bits
The algorithm for programming the Lock bits is as follows (refer to “Programming the Flash” on
page 237 for details on Command and Data loading):
1. A: Load Command “0010 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs the Lock bit. If LB mode 3 is programmed
(LB1 and LB2 is programmed), it is not possible to program the Boot Lock Bits by any
external Programming mode.
3. Give WR a negative pulse and wait for RDY/BSY to go high.
The Lock bits can only be cleared by executing Chip Erase.
Reading the Fuse and
Lock Bits
The algorithm for reading the Fuse and Lock bits is as follows (refer to “Programming the Flash”
on page 237 for details on Command loading):
1. A: Load Command “0000 0100”.
2. Set OE to “0”, BS2 to “0” and BS1 to “0”. The status of the Fuse Low bits can now be
read at DATA (“0” means programmed).
3. Set OE to “0”, BS2 to “1” and BS1 to “1”. The status of the Fuse High bits can now be
read at DATA (“0” means programmed).
4. Set OE to “0”, BS2 to “1” and BS1 to “0”. The status of the Extended Fuse bits can now
be read at DATA (“0” means programmed).
5. Set OE to “0”, BS2 to “0” and BS1 to “1”. The status of the Lock bits can now be read at
DATA (“0” means programmed).
6. Set OE to “1”.
Figure 101. Mapping Between BS1, BS2 and the Fuse and Lock Bits During Read
Reading the Signature
Bytes
The algorithm for reading the signature bytes is as follows (refer to “Programming the Flash” on
page 237 for details on Command and Address loading):
1. A: Load Command “0000 1000”.
2. B: Load Address Low Byte (0x00 - 0x02).
3. Set OE to “0”, and BS to “0”. The selected Signature byte can now be read at DATA.
4. Set OE to “1”.
Lock Bits 0
1
BS2
Fuse High Byte
0
1
BS1
DATA
Fuse Low Byte 0
1
BS2
Extended Fuse Byte
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Reading the
Calibration Byte
The algorithm for reading the calibration byte is as follows (refer to “Programming the Flash” on
page 237 for details on Command and Address loading):
1. A: Load Command “0000 1000”.
2. B: Load Address Low Byte, 0x00.
3. Set OE to “0”, and BS1 to “1”. The Calibration byte can now be read at DATA.
4. Set OE to “1”.
Parallel Programming
Characteristics
Figure 102. Parallel Programming Timing, Including some General Timing Requirements
Figure 103. Parallel Programming Timing, Loading Sequence with Timing Requirements(1)
Note: 1. The timing requirements shown in Figure 102 (i.e., tDVXH, tXHXL, and tXLDX) also apply to load-
ing operation.
Data & Contol
(DATA, XA0/1, BS1, BS2)
XTAL1
t
XHXL
t
WLWH
t
DVXH
t
XLDX
t
PLWL
t
WLRH
WR
RDY/BSY
PAGEL
t
PHPL
t
PLBX
t
BVPH
t
XLWL
t
WLBX
t
BVWL
WLRL
XTAL1
PAGEL
t
PLXH
XLXH
tt
XLPH
ADDR0 (low byte) DATA (low byte) DATA (high byte) ADDR1 (low byte)
DATA
BS1
XA0
XA1
LOAD ADDRESS
(LOW BYTE)
LOAD DATA
(LOW BYTE)
LOAD DATA
(HIGH BYTE)
LOAD DATA
LOAD ADDRESS
(LOW BYTE)
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Figure 104. Parallel Programming Timing, Reading Sequence (within the Same Page) with
Timing Requirements(1)
Note: 1. The timing requirements shown in Figure 102 (i.e., tDVXH, tXHXL, and tXLDX) also apply to read-
ing operation.
Table 107. Parallel Programming Characteristics, VCC = 5 V ± 10%
Symbol Parameter Min Typ Max Units
VPP Programming Enable Voltage 11.5 12.5 V
IPP Programming Enable Current 250 μA
tDVXH Data and Control Valid before XTAL1 High 67 ns
tXLXH XTAL1 Low to XTAL1 High 200 ns
tXHXL XTAL1 Pulse Width High 150 ns
tXLDX Data and Control Hold after XTAL1 Low 67 ns
tXLWL XTAL1 Low to WR Low 0 ns
tXLPH XTAL1 Low to PAGEL high 0 ns
tPLXH PAGEL low to XTAL1 high 150 ns
tBVPH BS1 Valid before PAGEL High 67 ns
tPHPL PAGEL Pulse Width High 150 ns
tPLBX BS1 Hold after PAGEL Low 67 ns
tWLBX BS2/1 Hold after WR Low 67 ns
tPLWL PAGEL Low to WR Low 67 ns
tBVWL BS1 Valid to WR Low 67 ns
tWLWH WR Pulse Width Low 150 ns
tWLRL WR Low to RDY/BSY Low 0 1 μs
tWLRH WR Low to RDY/BSY High(1) 3.7 4.5 ms
tWLRH_CE WR Low to RDY/BSY High for Chip Erase(2) 7.5 9 ms
tXLOL XTAL1 Low to OE Low 0 ns
XTAL1
OE
ADDR0 (low byte) DATA (low byte) DATA (high byte) ADDR1 (low byte)
DATA
BS1
XA0
XA1
LOAD ADDRESS
(LOW BYTE)
READ DATA
(LOW BYTE)
READ DATA
(HIGH BYTE)
LOAD ADDRESS
(LOW BYTE)
t
BVDV
t
OLDV
t
XLOL
t
OHDZ
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Notes: 1. tWLRH is valid for the Write Flash, Write EEPROM, Write Fuse Bits and Write Lock Bits
commands.
2. tWLRH_CE is valid for the Chip Erase command.
Serial
Downloading
SPI Serial
Programming Pin
Mapping
Both the Flash and EEPROM memory arrays can be programmed using the serial SPI bus while
RESET is pulled to GND. The serial interface consists of pins SCK, MOSI (input) and MISO (out-
put). After RESET is set low, the Programming Enable instruction needs to be executed first
before program/erase operations can be executed. NOTE, in Table 108 on page 245, the pin
mapping for SPI programming is listed. Not all parts use the SPI pins dedicated for the internal
SPI interface.
Figure 105. SPI Serial Programming and Verify(1)
Note: 1. If the device is clocked by the Internal Oscillator, it is no need to connect a clock source to the
XTAL1 pin.
When programming the EEPROM, an auto-erase cycle is built into the self-timed programming
operation (in the Serial mode ONLY) and there is no need to first execute the Chip Erase
instruction. The Chip Erase operation turns the content of every memory location in both the
Program and EEPROM arrays into 0xFF.
tBVDV BS1 Valid to DATA valid 0 250 ns
tOLDV OE Low to DATA Valid 250 ns
tOHDZ OE High to DATA Tri-stated 250 ns
Table 107. Parallel Programming Characteristics, VCC = 5 V ± 10% (Continued)
Symbol Parameter Min Typ Max Units
Table 108. Pin Mapping SPI Serial Programming
Symbol Pins I/O Description
MOSI PB5 I Serial Data in
MISO PB6 O Serial Data out
SCK PB7 I Serial Clock
VCC
GND
XTAL1
SCK
MISO
MOSI
RESET
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Depending on CKSEL Fuses, a valid clock must be present. The minimum low and high periods
for the serial clock (SCK) input are defined as follows:
Low:> 2 CPU clock cycles for fck < 12 MHz, 3 CPU clock cycles for fck >= 12 MHz
High:> 2 CPU clock cycles for fck < 12 MHz, 3 CPU clock cycles for fck >= 12 MHz
SPI Serial
Programming
Algorithm
When writing serial data to the ATmega162, data is clocked on the rising edge of SCK.
When reading data from the ATmega162, data is clocked on the falling edge of SCK. See Figure
106.
To program and verify the ATmega162 in the SPI Serial Programming mode, the following
sequence is recommended (See four byte instruction formats in Table 110):
1. Power-up sequence:
Apply power between VCC and GND while RESET and SCK are set to “0”. In some sys-
tems, the programmer can not guarantee that SCK is held low during Power-up. In this
case, RESET must be given a positive pulse of at least two CPU clock cycles duration
after SCK has been set to “0”.
2. Wait for at least 20 ms and enable SPI Serial Programming by sending the Programming
Enable serial instruction to pin MOSI.
3. The SPI Serial Programming instructions will not work if the communication is out of syn-
chronization. When in sync. the second byte (0x53), will echo back when issuing the third
byte of the Programming Enable instruction. Whether the echo is correct or not, all four
bytes of the instruction must be transmitted. If the 0x53 did not echo back, give RESET a
positive pulse and issue a new Programming Enable command.
4. The Flash is programmed one page at a time. The page size is found in Table 105 on
page 236. The memory page is loaded one byte at a time by supplying the 6 LSB of the
address and data together with the Load Program Memory Page instruction. To ensure
correct loading of the page, the data low byte must be loaded before data high byte is
applied for a given address. The Program Memory Page is stored by loading the Write
Program Memory Page instruction with the 8 MSB of the address. If polling is not used,
the user must wait at least tWD_FLASH before issuing the next page. (See Table 109.)
Accessing the SPI serial programming interface before the Flash write operation com-
pletes can result in incorrect programming.
5. The EEPROM array can either be programmed one page at a time or it can be pro-
grammed byte by byte.
For Page Programming, the following algorithm is used:
The EEPROM memory page is loaded one byte at a time by supplying the 2 LSB of the
address and data together with the Load EEPROM Memory Page instruction. The EEPROM
Memory Page is stored by loading the Write EEPROM Memory Page instruction with the 8
MSB of the address. If polling is not used, the user must wait at least tWD_EEPROM before issu-
ing the next page. (See Table 99.) Accessing the SPI Serial Programming interface before
the EEPROM write operation completes can result in incorrect programming.
Alternatively, the EEPROM can be programmed bytewise:
The EEPROM array is programmed one byte at a time by supplying the address and data
together with the Write EEPROM instruction. An EEPROM memory location is first automat-
ically erased before new data is written. If polling is not used, the user must wait at least
tWD_EEPROM before issuing the next byte. (See Table 109.) In a chip erased device, no 0xFFs
in the data file(s) need to be programmed.
6. Any memory location can be verified by using the Read instruction which returns the con-
tent at the selected address at serial output MISO.
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7. At the end of the programming session, RESET can be set high to commence normal
operation.
8. Power-off sequence (if needed):
Set RESET to “1”.
Tur n V CC power off.
Figure 106. SPI Serial Programming Waveforms
Table 109. Minimum Wait Delay before Writing the Next Flash or EEPROM Location
Symbol Minimum Wait Delay
tWD_FLASH 4.5 ms
tWD_EEPROM 9.0 ms
tWD_ERASE 9.0 ms
tWD_FUSE 4.5 ms
MSB
MSB
LSB
LSB
SERIAL CLOCK INPUT
(SCK)
SERIAL DATA INPUT
(MOSI)
(MISO)
SAMPLE
SERIAL DATA OUTPUT
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Table 110. SPI Serial Programming Instruction Set(1)
Instruction Instruction Format Operation
Byte 1 Byte 2 Byte 3 Byte4
Programming Enable 1010 1100 0101 0011 xxxx xxxx xxxx xxxx Enable SPI Serial Programming
after RESET goes low.
Chip Erase 1010 1100 100x xxxx xxxx xxxx xxxx xxxx Chip Erase EEPROM and Flash.
Read Program Memory
0010 H000 00aa aaaa bbbb bbbb oooo oooo Read H (high or low) data o from
Program memory at word address
a:b.
Load Program Memory
Page
0100 H000 00xx xxxx xxbb bbbb iiii iiii Write H (high or low) data i to
Program Memory page at word
address b. Data low byte must be
loaded before Data high byte is
applied within the same address.
Write Program Memory
Page
0100 1100 00aa aaaa bbxx xxxx xxxx xxxx Write Program Memory Page at
address a:b.
Read EEPROM Memory 1010 0000 00xx xxaa bbbb bbbb oooo oooo Read data o from EEPROM
memory at address a:b.
Write EEPROM Memory
(byte access)
1100 0000 00xx xxaa bbbb bbbb iiii iiii Write data i to EEPROM memory
at address a:b.
Load EEPROM Memory
Page (page access)
1100 0001 0000 0000 0000 00bb iiii iiii Load data i to EEPROM memory
page buffer. After data is loaded,
program EEPROM page.
Write EEPROM Memory
Page (page access)
1100 0010 00xx xxaa bbbb bb00 xxxx xxxx Write EEPROM page at address
a:b.
Read Lock Bits
0101 1000 0000 0000 xxxx xxxx xxoo oooo Read Lock bits. “0” = programmed,
“1” = unprogrammed. See Table
96 on page 231 for details.
Write Lock Bits
1010 1100 111x xxxx xxxx xxxx 11ii iiii Write Lock bits. Set bits = “0” to
program Lock bits. See Table 96
on page 231 for details.
Read Signature Byte 0011 0000 00xx xxxx xxxx xxbb oooo oooo Read Signature Byte o at address
b.
Write Fuse Bits
1010 1100 1010 0000 xxxx xxxx iiii iiii Set bits = “0” to program, “1” to
unprogram. See Table 100 on
page 233 for details.
Write Fuse High Bits
1010 1100 1010 1000 xxxx xxxx iiii iiii Set bits = “0” to program, “1” to
unprogram. See Table 99 on
page 233 for details.
Write Extended Fuse Bits
1010 1100 1010 0100 xxxx xxxx xxxx xxii Set bits = “0” to program, “1” to
unprogram. See Table 98 on
page 232 for details.
Read Fuse Bits
0101 0000 0000 0000 xxxx xxxx oooo oooo Read Fuse bits. “0” = programmed,
“1” = unprogrammed. See Table
100 on page 233 for details.
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Note: 1. a = address high bits, b = address low bits, H = 0 – Low byte, 1 – High Byte, o = data out, i = data in, x = don’t care
SPI Serial
Programming
Characteristics
For characteristics of the SPI module, see “SPI Timing Characteristics” on page 268.
Read Fuse High Bits
0101 1000 0000 1000 xxxx xxxx oooo oooo Read Fuse high bits. “0” = pro-
grammed, “1” = unprogrammed.
See Table 99 on page 233 for
details.
Read Extended Fuse Bits
0101 0000 0000 1000 xxxx xxxx oooo oooo Read Extended Fuse bits. “0” =
pro-grammed, “1” =
unprogrammed. See Table 98 on
page 232 for details.
Read Calibration Byte 0011 1000 00xx xxxx 0000 0000 oooo oooo Read Calibration Byte
Poll RDY/BSY
1111 0000 0000 0000 xxxx xxxx xxxx xxxoIf o = “1”, a programming operation
is still busy. Wait until this bit
returns to “0” before applying
another command.
Table 110. SPI Serial Programming Instruction Set(1) (Continued)
Instruction Instruction Format Operation
Byte 1 Byte 2 Byte 3 Byte4
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Programming via
the JTAG Interface
Programming through the JTAG interface requires control of the four JTAG specific pins: TCK,
TMS, TDI, and TDO. Control of the Reset and clock pins is not required.
To be able to use the JTAG interface, the JTAGEN Fuse must be programmed. The device is
default shipped with the Fuse programmed. In addition, the JTD bit in MCUCSR must be
cleared. Alternatively, if the JTD bit is set, the External Reset can be forced low. Then, the JTD
bit will be cleared after two chip clocks, and the JTAG pins are available for programming. This
provides a means of using the JTAG pins as normal port pins in running mode while still allowing
In-System Programming via the JTAG interface. Note that this technique can not be used when
using the JTAG pins for Boundary-scan or On-chip Debug. In these cases the JTAG pins must
be dedicated for this purpose.
As a definition in this datasheet, the LSB is shifted in and out first of all Shift Registers.
Programming Specific
JTAG Instructions
The Instruction Register is 4-bit wide, supporting up to 16 instructions. The JTAG instructions
useful for Programming are listed below.
The OPCODE for each instruction is shown behind the instruction name in hex format. The text
describes which Data Register is selected as path between TDI and TDO for each instruction.
The Run-Test/Idle state of the TAP controller is used to generate internal clocks. It can also be
used as an idle state between JTAG sequences. The state machine sequence for changing the
instruction word is shown in Figure 107.
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Figure 107. State machine sequence for changing the instruction word
Test-Logic-Reset
Run-Test/Idle
Shift-DR
Exit1-DR
Pause-DR
Exit2-DR
Update-DR
Select-IR Scan
Capture-IR
Shift-IR
Exit1-IR
Pause-IR
Exit2-IR
Update-IR
Select-DR Scan
Capture-DR
0
1
011 1
00
00
11
10
1
1
0
1
0
0
10
1
1
0
1
0
0
00
11
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AVR_RESET (0xC) The AVR specific public JTAG instruction for setting the AVR device in the Reset mode or taking
the device out from the Reset mode. The TAP controller is not reset by this instruction. The one
bit Reset Register is selected as data register. Note that the reset will be active as long as there
is a logic “one” in the Reset Chain. The output from this chain is not latched.
The active states are:
• Shift-DR: The Reset Register is shifted by the TCK input.
PROG_ENABLE (0x4) The AVR specific public JTAG instruction for enabling programming via the JTAG port. The 16-
bit Programming Enable Register is selected as data register. The active states are the
following:
• Shift-DR: The programming enable signature is shifted into the Data Register.
• Update-DR: The programming enable signature is compared to the correct value, and
Programming mode is entered if the signature is valid.
PROG_COMMANDS
(0x5)
The AVR specific public JTAG instruction for entering programming commands via the JTAG
port. The 15-bit Programming Command Register is selected as data register. The active states
are the following:
• Capture-DR: The result of the previous command is loaded into the Data Register.
• Shift-DR: The Data Register is shifted by the TCK input, shifting out the result of the
previous command and shifting in the new command.
• Update-DR: The programming command is applied to the Flash inputs.
• Run-Test/Idle: One clock cycle is generated, executing the applied command (not always
required, see Table 111 below).
PROG_PAGELOAD
(0x6)
The AVR specific public JTAG instruction to directly load the Flash data page via the JTAG port.
The 1024 bit Virtual Flash Page Load Register is selected as register. This is a virtual scan chain
with length equal to the number of bits in one Flash page. Internally the Shift Register is 8-bit.
Unlike most JTAG instructions, the Update-DR state is not used to transfer data from the Shift
Register. The data are automatically transferred to the Flash page buffer byte-by-byte in the
Shift-DR state by an internal state machine. This is the only active state:
• Shift-DR: Flash page data are shifted in from TDI by the TCK input, and automatically
loaded into the Flash page one byte at a time.
Note: The JTAG instruction PROG_PAGELOAD can only be used if the AVR device is the first device in
JTAG scan chain. If the AVR cannot be the first device in the scan chain, the byte-wise program-
ming algorithm must be used.
PROG_PAGEREAD
(0x7)
The AVR specific public JTAG instruction to read one full Flash data page via the JTAG port.
The 1032 bit Virtual Flash Page Read Register is selected as data register. This is a virtual scan
chain with length equal to the number of bits in one Flash page plus eight. Internally the Shift
Register is 8-bit. Unlike most JTAG instructions, the Capture-DR state is not used to transfer
data to the Shift Register. The data are automatically transferred from the Flash page buffer
byte-by-byte in the Shift-DR state by an internal state machine. This is the only active state:
• Shift-DR: Flash data are automatically read one byte at a time and shifted out on TDO by the
TCK input. The TDI input is ignored.
Note: The JTAG instruction PROG_PAGEREAD can only be used if the AVR device is the first device in
JTAG scan chain. If the AVR cannot be the first device in the scan chain, the byte-wise program-
ming algorithm must be used.
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Data Registers The Data Registers are selected by the JTAG Instruction Registers described in section “Pro-
gramming Specific JTAG Instructions” on page 250. The Data Registers relevant for
programming operations are:
• Reset Register
• Programming Enable Register.
• Programming Command Register.
• Virtual Flash Page Load Register.
• Virtual Flash Page Read Register.
Reset Register The Reset Register is a test data register used to reset the part during programming. It is
required to reset the part before entering Programming mode.
A high value in the Reset Register corresponds to pulling the external reset low. The part is reset
as long as there is a high value present in the Reset Register. Depending on the fuse settings for
the clock options, the part will remain reset for a Reset Time-out period (refer to “Clock Sources”
on page 36) after releasing the Reset Register. The output from this data register is not latched,
so the reset will take place immediately, as shown in Figure 86 on page 206.
Programming Enable
Register
The Programming Enable Register is a 16-bit register. The contents of this register is compared
to the programming enable signature, binary code 1010_0011_0111_0000. When the contents
of the register is equal to the programming enable signature, programming via the JTAG port is
enabled. The register is reset to 0 on Power-on Reset, and should always be reset when leaving
Programming mode.
Figure 108. Programming Enable Register
TDI
TDO
D
A
T
A
=DQ
ClockDR & PROG_ENABLE
Programming Enable
0xA370
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Programming
Command Register
The Programming Command Register is a 15-bit register. This register is used to serially shift in
programming commands, and to serially shift out the result of the previous command, if any. The
JTAG Programming Instruction Set is shown in Table 111. The state sequence when shifting in
the programming commands is illustrated in Figure 110.
Figure 109. Programming Command Register
TDI
TDO
S
T
R
O
B
E
S
A
D
D
R
E
S
S
/
D
A
T
A
Flash
EEPROM
Fuses
Lock Bits
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Table 111. JTAG Programming Instruction Set
Instruction TDI sequence TDO sequence Notes
1a. Chip eRase 0100011_10000000
0110001_10000000
0110011_10000000
0110011_10000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
1b. Poll for Chip Erase complete 0110011_10000000 xxxxxox_xxxxxxxx (2)
2a. Enter Flash Write 0100011_00010000 xxxxxxx_xxxxxxxx
2b. Load Address High Byte 0000111_aaaaaaaa xxxxxxx_xxxxxxxx (9)
2c. Load Address Low Byte 0000011_bbbbbbbb xxxxxxx_xxxxxxxx
2d. Load Data Low Byte 0010011_iiiiiiii xxxxxxx_xxxxxxxx
2e. Load Data High Byte 0010111_iiiiiiii xxxxxxx_xxxxxxxx
2f. Latch Data 0110111_00000000
1110111_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
2g. Write Flash Page 0110111_00000000
0110101_00000000
0110111_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
2h. Poll for Page Write complete 0110111_00000000 xxxxxox_xxxxxxxx (2)
3a. Enter Flash Read 0100011_00000010 xxxxxxx_xxxxxxxx
3b. Load Address High Byte 0000111_aaaaaaaa xxxxxxx_xxxxxxxx (9)
3c. Load Address Low Byte 0000011_bbbbbbbb xxxxxxx_xxxxxxxx
3d. Read Data Low and High Byte 0110010_00000000
0110110_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
xxxxxxx_oooooooo
low byte
high byte
4a. Enter EEPROM Write 0100011_00010001 xxxxxxx_xxxxxxxx
4b. Load Address High Byte 0000111_aaaaaaaa xxxxxxx_xxxxxxxx (9)
4c. Load Address Low Byte 0000011_bbbbbbbb xxxxxxx_xxxxxxxx
4d. Load Data Byte 0010011_iiiiiiii xxxxxxx_xxxxxxxx
4e. Latch Data 0110111_00000000
1110111_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
4f. Write EEPROM Page 0110011_00000000
0110001_00000000
0110011_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
4g. Poll for Page Write complete 0110011_00000000 xxxxxox_xxxxxxxx (2)
5a. Enter EEPROM Read 0100011_00000011 xxxxxxx_xxxxxxxx
5b. Load Address High Byte 0000111_aaaaaaaa xxxxxxx_xxxxxxxx (9)
5c. Load Address Low Byte 0000011_bbbbbbbb xxxxxxx_xxxxxxxx
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5d. Read Data Byte 0110011_bbbbbbbb
0110010_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
6a. Enter Fuse Write 0100011_01000000 xxxxxxx_xxxxxxxx
6b. Load Data Low Byte(6) 0010011_iiiiiiii xxxxxxx_xxxxxxxx (3)
6c. Write Fuse Extended Byte 0111011_00000000
0111001_00000000
0111011_00000000
0111011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
6d. Poll for Fuse Write complete 0110111_00000000 xxxxxox_xxxxxxxx (2)
6e. Load Data Low Byte(7) 0010011_iiiiiiii xxxxxxx_xxxxxxxx (3)
6f. Write Fuse High byte 0110111_00000000
0110101_00000000
0110111_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
6g. Poll for Fuse Write complete 0110111_00000000 xxxxxox_xxxxxxxx (2)
6h. Load Data Low Byte(8) 0010011_iiiiiiii xxxxxxx_xxxxxxxx (3)
6i. Write Fuse Low Byte 0110011_00000000
0110001_00000000
0110011_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
6j. Poll for Fuse Write complete 0110011_00000000 xxxxxox_xxxxxxxx (2)
7a. Enter Lock Bit Write 0100011_00100000 xxxxxxx_xxxxxxxx
7b. Load Data Byte(9) 0010011_11iiiiii xxxxxxx_xxxxxxxx (4)
7c. Write Lock Bits 0110011_00000000
0110001_00000000
0110011_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
(1)
7d. Poll for Lock Bit Write complete 0110011_00000000 xxxxxox_xxxxxxxx (2)
8a. Enter Fuse/Lock Bit Read 0100011_00000100 xxxxxxx_xxxxxxxx
8b. Read Fuse Extended Byte(6) 0111010_00000000
0111111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
8c. Read Fuse High Byte(7) 0111110_00000000
0111111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
8d. Read Fuse Low Byte(8) 0110010_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
8e. Read Lock Bits(9) 0110110_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxoooooo
(5)
Table 111. JTAG Programming Instruction Set (Continued)
Instruction TDI sequence TDO sequence Notes
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Notes: 1. This command sequence is not required if the seven MSB are correctly set by the previous command sequence (which is
normally the case).
2. Repeat until o = “1”.
3. Set bits to “0” to program the corresponding Fuse, “1” to unprogram the Fuse.
4. Set bits to “0” to program the corresponding lock bit, “1” to leave the Lock bit unchanged.
5. “0” = programmed, “1” = unprogrammed.
6. The bit mapping for Fuses Extended byte is listed in Table 98 on page 232.
7. The bit mapping for Fuses High byte is listed in Table 99 on page 233.
8. The bit mapping for Fuses Low byte is listed in Table 100 on page 233.
9. The bit mapping for Lock Bits byte is listed in Table 96 on page 231.
10. Address bits exceeding PCMSB and EEAMSB (Table 105 and Table 106) are don’t care
Note: a = address high bits
b = address low bits
H = 0 – Low byte, 1 – High Byte
o = data out
i = data in
x = don’t care
8f. Read Fuses and Lock Bits 0111010_00000000
0111110_00000000
0110010_00000000
0110110_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
xxxxxxx_oooooooo
xxxxxxx_oooooooo
xxxxxxx_oooooooo
(5)
Fuse ext. byte
Fuse high byte
Fuse low byte
Lock bits
9a. Enter Signature Byte Read 0100011_00001000 xxxxxxx_xxxxxxxx
9b. Load Address Byte 0000011_bbbbbbbb xxxxxxx_xxxxxxxx
9c. Read Signature Byte 0110010_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
10a. Enter Calibration Byte Read 0100011_00001000 xxxxxxx_xxxxxxxx
10b. Load Address Byte 0000011_bbbbbbbb xxxxxxx_xxxxxxxx
10c. Read Calibration Byte 0110110_00000000
0110111_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_oooooooo
11a. Load No Operation Command 0100011_00000000
0110011_00000000
xxxxxxx_xxxxxxxx
xxxxxxx_xxxxxxxx
Table 111. JTAG Programming Instruction Set (Continued)
Instruction TDI sequence TDO sequence Notes
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Figure 110. State Machine Sequence for Changing/Reading the Data Word
Virtual Flash Page
Load Register
The Virtual Flash Page Load Register is a virtual scan chain with length equal to the number of
bits in one Flash page. Internally the Shift Register is 8-bit, and the data are automatically trans-
ferred to the Flash page buffer byte-by-byte. Shift in all instruction words in the page, starting
with the LSB of the first instruction in the page and ending with the MSB of the last instruction in
the page. This provides an efficient way to load the entire Flash page buffer before executing
Page Write.
Test-Logic-Reset
Run-Test/Idle
Shift-DR
Exit1-DR
Pause-DR
Exit2-DR
Update-DR
Select-IR Scan
Capture-IR
Shift-IR
Exit1-IR
Pause-IR
Exit2-IR
Update-IR
Select-DR Scan
Capture-DR
0
1
011 1
00
00
11
10
1
1
0
1
0
0
10
1
1
0
1
0
0
00
11
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Figure 111. Virtual Flash Page Load Register
Virtual Flash Page
Read Register
The Virtual Flash Page Read Register is a virtual scan chain with length equal to the number of
bits in one Flash page plus eight. Internally the Shift Register is 8-bit, and the data are automati-
cally transferred from the Flash data page byte-by-byte. The first eight cycles are used to
transfer the first byte to the internal Shift Register, and the bits that are shifted out during these
right cycles should be ignored. Following this initialization, data are shifted out starting with the
LSB of the first instruction in the page and ending with the MSB of the last instruction in the
page. This provides an efficient way to read one full Flash page to verify programming.
TDI
TDO
D
A
T
A
Flash
EEPROM
Fuses
Lock Bits
STROBES
ADDRESS
State
Machine
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Figure 112. Virtual Flash Page Read Register
Programming
Algorithm
All references below of type “1a”, “1b”, and so on, refer to Table 111.
Entering Programming
Mode
1. Enter JTAG instruction AVR_RESET and shift one in the Reset Register.
2. Enter instruction PROG_ENABLE and shift 1010_0011_0111_0000 in the Programming
Enable Register.
Leaving Programming
Mode
1. Enter JTAG instruction PROG_COMMANDS.
2. Disable all programming instructions by using no operation instruction 11a.
3. Enter instruction PROG_ENABLE and shift 0000_0000_0000_0000 in the Programming
Enable Register.
4. Enter JTAG instruction AVR_RESET and shift 0 in the Reset Register.
Performing Chip Erase 1. Enter JTAG instruction PROG_COMMANDS.
2. Start Chip Erase using programming instruction 1a.
3. Poll for Chip Erase complete using programming instruction 1b, or wait for tWLRH_CE (refer
to Table 107 on page 244).
Programming the
Flash
Before programming the Flash a Chip Erase must be performed. See “Performing Chip Erase”
on page 260.
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Flash write using programming instruction 2a.
3. Load address high byte using programming instruction 2b.
4. Load address low byte using programming instruction 2c.
5. Load data using programming instructions 2d, 2e and 2f.
6. Repeat steps 4 and 5 for all instruction words in the page.
TDI
TDO
D
A
T
A
Flash
EEPROM
Fuses
Lock Bits
STROBES
ADDRESS
State
Machine
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7. Write the page using programming instruction 2g.
8. Poll for Flash write complete using programming instruction 2h, or wait for tWLRH_FLASH
(refer to Table 107 on page 244).
9. Repeat steps 3 to 7 until all data have been programmed.
A more efficient data transfer can be achieved using the PROG_PAGELOAD instruction:
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Flash write using programming instruction 2a.
3. Load the page address using programming instructions 2b and 2c. PCWORD (refer to
Table 105 on page 236) is used to address within one page and must be written as 0.
4. Enter JTAG instruction PROG_PAGELOAD.
5. Load the entire page by shifting in all instruction words in the page, starting with the LSB
of the first instruction in the page and ending with the MSB of the last instruction in the
page.
6. Enter JTAG instruction PROG_COMMANDS.
7. Write the page using programming instruction 2g.
8. Poll for Flash write complete using programming instruction 2h, or wait for tWLRH_FLASH
(refer to Table 107 on page 244).
9. Repeat steps 3 to 8 until all data have been programmed.
Reading the Flash 1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Flash read using programming instruction 3a.
3. Load address using programming instructions 3b and 3c.
4. Read data using programming instruction 3d.
5. Repeat steps 3 and 4 until all data have been read.
A more efficient data transfer can be achieved using the PROG_PAGEREAD instruction:
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Flash read using programming instruction 3a.
3. Load the page address using programming instructions 3b and 3c. PCWORD (refer to
Table 105 on page 236) is used to address within one page and must be written as 0.
4. Enter JTAG instruction PROG_PAGEREAD.
5. Read the entire page by shifting out all instruction words in the page, starting with the
LSB of the first instruction in the page and ending with the MSB of the last instruction in
the page. Remember that the first 8 bits shifted out should be ignored.
6. Enter JTAG instruction PROG_COMMANDS.
7. Repeat steps 3 to 6 until all data have been read.
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Programming the
EEPROM
Before programming the EEPROM a Chip Erase must be performed. See “Performing Chip
Erase” on page 260.
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable EEPROM write using programming instruction 4a.
3. Load address high byte using programming instruction 4b.
4. Load address low byte using programming instruction 4c.
5. Load data using programming instructions 4d and 4e.
6. Repeat steps 4 and 5 for all data bytes in the page.
7. Write the data using programming instruction 4f.
8. Poll for EEPROM write complete using programming instruction 4g, or wait for tWLRH
(refer to Table 107 on page 244).
9. Repeat steps 3 to 8 until all data have been programmed.
Note: The PROG_PAGELOAD instruction can not be used when programming the EEPROM
Reading the EEPROM 1. Enter JTAG instruction PROG_COMMANDS.
2. Enable EEPROM read using programming instruction 5a.
3. Load address using programming instructions 5b and 5c.
4. Read data using programming instruction 5d.
5. Repeat steps 3 and 4 until all data have been read.
Note: The PROG_PAGEREAD instruction can not be used when reading the EEPROM
Programming the
Fuses
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Fuse write using programming instruction 6a.
3. Load data low byte using programming instructions 6b. A bit value of “0” will program the
corresponding Fuse, a “1” will unprogram the Fuse.
4. Write Fuse extended byte using programming instruction 6c.
5. Poll for Fuse write complete using programming instruction 6d, or wait for tWLRH (refer to
Table 107 on page 244).
6. Load data low byte using programming instructions 6e. A bit value of “0” will program the
corresponding Fuse, a “1” will unprogram the Fuse.
7. Write Fuse High byte using programming instruction 6f.
8. Poll for Fuse write complete using programming instruction 6g, or wait for tWLRH (refer to
Table 107 on page 244).
9. Load data low byte using programming instructions 6h. A “0” will program the Fuse, a “1”
will unprogram the Fuse.
10. Write Fuse Low byte using programming instruction 6i.
11. Poll for Fuse write complete using programming instruction 6j, or wait for tWLRH (refer to
Table 107 on page 244).
Programming the Lock
Bits
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Lock bit write using programming instruction 7a.
3. Load data using programming instructions 7b. A bit value of “0” will program the corre-
sponding Lock bit, a “1” will leave the Lock bit unchanged.
4. Write Lock bits using programming instruction 7c.
5. Poll for Lock bit write complete using programming instruction 7d, or wait for tWLRH (refer
to Table 107 on page 244).
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Reading the Fuses
and Lock Bits
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Fuse/Lock bit read using programming instruction 8a.
3. To read all Fuses and Lock bits, use programming instruction 8f.
To only read Fuse Extended byte, use programming instruction 8b.
To only read Fuse High byte, use programming instruction 8c.
To only read Fuse Low byte, use programming instruction 8d.
To only read Lock bits, use programming instruction 8e.
Reading the Signature
Bytes
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Signature byte read using programming instruction 9a.
3. Load address 0x00 using programming instruction 9b.
4. Read first signature byte using programming instruction 9c.
5. Repeat steps 3 and 4 with address 0x01 and address 0x02 to read the second and third
signature bytes, respectively.
Reading the
Calibration Byte
1. Enter JTAG instruction PROG_COMMANDS.
2. Enable Calibration byte read using programming instruction 10a.
3. Load address 0x00 using programming instruction 10b.
4. Read the calibration byte using programming instruction 10c.
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Electrical Characteristics
DC Characteristics
Absolute Maximum Ratings*
Operating Temperature.................................. -55°C to +125°C*NOTICE: Stresses beyond those listed under “Absolute
Maximum Ratings” may cause permanent dam-
age to the device. This is a stress rating only and
functional operation of the device at these or
other conditions beyond those indicated in the
operational sections of this specification is not
implied. Exposure to absolute maximum rating
conditions for extended periods may affect device
reliability.
Storage Temperature ..................................... -65°C to +150°C
Voltage on any Pin except RESET
with respect to Ground ................................-0.5V to VCC+0.5V
Voltage on RESET with respect to Ground......-0.5V to +13.0V
Maximum Operating Voltage ............................................ 6.0V
DC Current per I/O Pin ............................................... 40.0 mA
DC Current VCC and GND Pins.......................200.0 mA PDIP,
400 mA TQFP/MLF
TA = -40°C to 85°C, VCC = 1.8V to 5.5V (unless otherwise noted)
Symbol Parameter Condition Min. Typ. Max. Units
VIL
Input Low Voltage, Except XTAL1
and RESETpin
VCC = 1.8 - 2.4V
VCC = 2.4 - 5.5V
-0.5
-0.5
0.2 VCC(1)
0.3 VCC(1) V
VIH
Input High Voltage, Except XTAL1
and RESET pin
VCC = 1.8 - 2.4V
VCC = 2.4 - 5.5V
0.7 VCC(2)
0.6 VCC(2)
VCC + 0.5
VCC + 0.5 V
VIL1 Input Low Voltage, XTAL1 pin VCC = 1.8 - 5.5V -0.5 0.1 VCC(1) V
VIH1 Input High Voltage, XTAL1 pin VCC = 1.8 - 2.4V
VCC = 2.4 - 5.5V
0.8 VCC(2)
0.7 VCC(2)
VCC + 0.5
VCC + 0.5 V
VIL2 Input Low Voltage, RESET pin VCC = 1.8 - 5.5V -0.5 0.2 VCC V
VIH2 Input High Voltage, RESET pin VCC = 1.8 - 5.5V 0.9 VCC(2) VCC + 0.5 V
VOL
Output Low Voltage(3), Ports A, B, C,
D, and E
IOL = 20 mA, VCC = 5V
IOL = 10 mA, VCC = 3V
0.7
0.5
V
V
VOH
Output High Voltage(4), Ports A, B, C,
D, and E
IOL = -20 mA, VCC = 5V
IOL = -10 mA, VCC = 3V
4.2
2.3
V
V
IIL Input Leakage Current I/O Pin Vcc = 5.5V, p in l ow
(absolute value) 1µA
IIH Input Leakage Current I/O Pin Vcc = 5.5V, pin high
(absolute value) 1µA
RRST Reset Pull-up Resistor 30 60 kΩ
Rpu I/O Pin Pull-up Resistor 20 50 kΩ
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Notes: 1. “Max” means the highest value where the pin is guaranteed to be read as low
2. “Min” means the lowest value where the pin is guaranteed to be read as high
3. Although each I/O port can sink more than the test conditions (20 mA at Vcc = 5V, 10 mA at Vcc = 3V) under steady state
conditions (non-transient), the following must be observed:
PDIP Package:
1] The sum of all IOL, for all ports, should not exceed 200 mA.
2] The sum of all IOL, for port B0 - B7, D0 - D7, and XTAL2, should not exceed 100 mA.
3] The sum of all IOL, for ports A0 - A7, E0 - E2, C0 - C7, should not exceed 100 mA.
TQFP and QFN/MLF Package:
1] The sum of all IOL, for all ports, should not exceed 400 mA.
2] The sum of all IOL, for ports B0 - B7, D0 - D7, and XTAL2, should not exceed 200 mA.
3] The sum of all IOL, for ports C0 - C7 and E1 - E2, should not exceed 200 mA.
4] The sum of all IOL, for ports A0 - A7 and E0, should not exceed 200 mA.
If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current greater
than the listed test condition.
4. Although each I/O port can source more than the test conditions (20 mA at Vcc = 5V, 10 mA at Vcc = 3V) under steady state
conditions (non-transient), the following must be observed:
PDIP Package:
1] The sum of all IOH, for all ports, should not exceed 200 mA.
2] The sum of all IOH, for port B0 - B7, D0 - D7, and XTAL2, should not exceed 100 mA.
3] The sum of all IOH, for ports A0 - A7, E0 - E2, C0 - C7, should not exceed 100 mA.
TQFP and MLF Package:
1] The sum of all IOH, for all ports, should not exceed 400 mA.
2] The sum of all IOH, for ports B0 - B7, D0 - D7, and XTAL2, should not exceed 200 mA.
3] The sum of all IOH, for ports C0 - C7 and E1 - E2, should not exceed 200 mA.
4] The sum of all IOH, for ports A0 - A7 and E0, should not exceed 200 mA.
ICC
Power Supply Current
Active 1 MHz, VCC = 2V
(ATmega162V) 0.8 mA
Active 4 MHz, VCC = 3V
(ATmega162/V) 5mA
Active 8 MHz, VCC = 5V
(ATmega162) 16 mA
Idle 1 MHz, VCC = 2V
(ATmega162V) 0.3 mA
Idle 4 MHz, VCC = 3V
(ATmega162/V) 2mA
Idle 8 MHz, VCC = 5V
(ATmega162) 8mA
Power-down mode
WDT Enabled,
VCC = 3.0V < 10 14 µA
WDT Disabled,
VCC = 3.0V < 1.5 2 µA
VACIO
Analog Comparator Input Offset
Voltage
VCC = 5V
Vin = VCC/2 < 10 40 mV
IACLK
Analog Comparator Input Leakage
Current
VCC = 5V
Vin = VCC/2 -50 50 nA
tACPD
Analog Comparator Propagation
Delay
VCC = 2.7V
VCC = 4.0V
750
500 ns
TA = -40°C to 85°C, VCC = 1.8V to 5.5V (unless otherwise noted) (Continued)
Symbol Parameter Condition Min. Typ. Max. Units
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If IOH exceeds the test condition, VOH may exceed the related specification. Pins are not guaranteed to source current
greater than the listed test condition.
Figure 113. Absolute Maximum Frequency as a function of VCC, ATmega162V
Figure 114. Absolute Maximum Frequency as a function of VCC, ATmega162
Frequency
8 MHz
16 MHz
1 MHz
VCC
1.8V 2.4V 5.5V
2.7V 4.5V
Safe Operating
Area
Frequency
8 MHz
16 MHz
1 MHz
VCC
1.8V 2.4V 5.5V
2.7V 4.5V
Safe Operating
Area
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External Clock
Drive Waveforms
Figure 115. External Clock Drive Waveforms
External Clock
Drive
VIL1
VIH1
Table 112. External Clock Drive
Symbol Parameter
VCC = 1.8 - 5.5V VCC =2.7 - 5.5V VCC = 4.5 - 5.5V
UnitsMin. Max. Min. Max. Min. Max.
1/tCLCL
Oscillator
Frequency 0108016MHz
tCLCL Clock Period 1000 125 62.5 ns
tCHCX High Time 400 50 25 ns
tCLCX Low Time 400 50 25 ns
tCLCH Rise Time 2.0 1.6 0.5 μs
tCHCL Fall Time 2.0 1.6 0.5 μs
ΔtCLCL
Change in
period from one
clock cycle to
the next
22 2%
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SPI Timing
Characteristics
See Figure 116 and Figure 117 for details.
Note: 1. In SPI Programming mode, the minimum SCK high/low period is:
– 2 tCLCL for fCK < 12 MHz
– 3 tCLCL for fCK > 12 MHz.
Figure 116. SPI Interface Timing Requirements (Master Mode)
Table 113. SPI Timing Parameters
Description Mode Min Typ Max
1 SCK period Master See Table 68
ns
2 SCK high/low Master 50% duty cycle
3 Rise/Fall time Master 3.6
4 Setup Master 10
5 Hold Master 10
6 Out to SCK Master 0.5 • tsck
7 SCK to out Master 10
8 SCK to out high Master 10
9 SS low to out Slave 15
10 SCK period Slave 4 • tck
11 SCK high/low(1) Slave 2 • tck
12 Rise/Fall time Slave 1.6 µs
13 Setup Slave 10
ns
14 Hold Slave tck
15 SCK to out Slave 15
16 SCK to SS high Slave 20
17 SS high to tri-state Slave 10
18 SS low to SCK Slave 2 • tck
MOSI
(Data Output)
SCK
(CPOL = 1)
MISO
(Data Input)
SCK
(CPOL = 0)
SS
MSB LSB
LSBMSB
...
...
61
22
345
8
7
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Figure 117. SPI Interface Timing Requirements (Slave Mode)
MISO
(Data Output)
SCK
(CPOL = 1)
MOSI
(Data Input)
SCK
(CPOL = 0)
SS
MSB LSB
LSBMSB
...
...
10
11 11
1213 14
17
15
9
X
16
18
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External Data Memory Timing
Notes: 1. This assumes 50% clock duty cycle. The half period is actually the high time of the external clock, XTAL1.
2. This assumes 50% clock duty cycle. The half period is actually the low time of the external clock, XTAL1.
Table 114. External Data Memory Characteristics, 4.5 - 5.5 Volts, no Wait-state
Symbol Parameter
8 MHz Oscillator Variable Oscillator
UnitMin Max Min Max
01/t
CLCL Oscillator Frequency 0.0 16 MHz
1t
LHLL ALE Pulse Width 115 1.0tCLCL-10 ns
2t
AVLL Address Valid A to ALE Low 57.5 0.5tCLCL-5(1) ns
3a tLLAX_ST
Address Hold After ALE Low,
write access 55 ns
3b tLLAX_LD
Address Hold after ALE Low,
read access 55 ns
4t
AVLLC Address Valid C to ALE Low 57.5 0.5tCLCL-5(1) ns
5t
AVRL Address Valid to RD Low 115 1.0tCLCL-10 ns
6t
AVWL Address Valid to WR Low 115 1.0tCLCL-10 ns
7t
LLWL ALE Low to WR Low 47.5 67.5 0.5tCLCL-15(2) 0.5tCLCL+5(2) ns
8t
LLRL ALE Low to RD Low 47.5 67.5 0.5tCLCL-15(2) 0.5tCLCL+5(2) ns
9t
DVRH Data Setup to RD High 40 40 ns
10 tRLDV Read Low to Data Valid 75 1.0tCLCL-50 ns
11 tRHDX Data Hold After RD High 0 0 ns
12 tRLRH RD Pulse Width 115 1.0tCLCL-10 ns
13 tDVWL Data Setup to WR Low 42.5 0.5tCLCL-20(1) ns
14 tWHDX Data Hold After WR High 115 1.0tCLCL-10 ns
15 tDVWH Data Valid to WR High 125 1.0tCLCL ns
16 tWLWH WR Pulse Width 115 1.0tCLCL-10 ns
Table 115. External Data Memory Characteristics, 4.5 - 5.5 Volts, 1 Cycle Wait-state
Symbol Parameter
8 MHz Oscillator Variable Oscillator
UnitMin Max Min Max
01/t
CLCL Oscillator Frequency 0.0 16 MHz
10 tRLDV Read Low to Data Valid 200 2.0tCLCL-50 ns
12 tRLRH RD Pulse Width 240 2.0tCLCL-10 ns
15 tDVWH Data Valid to WR High 240 2.0tCLCL ns
16 tWLWH WR Pulse Width 240 2.0tCLCL-10 ns
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Table 116. External Data Memory Characteristics, 4.5 - 5.5 Volts, SRWn1 = 1, SRWn0 = 0
Symbol Parameter
4 MHz Oscillator Variable Oscillator
UnitMin Max Min Max
01/t
CLCL Oscillator Frequency 0.0 16 MHz
10 tRLDV Read Low to Data Valid 325 3.0tCLCL-50 ns
12 tRLRH RD Pulse Width 365 3.0tCLCL-10 ns
15 tDVWH Data Valid to WR High 375 3.0tCLCL ns
16 tWLWH WR Pulse Width 365 3.0tCLCL-10 ns
Table 117. External Data Memory Characteristics, 4.5 - 5.5 Volts, SRWn1 = 1, SRWn0 = 1
Symbol Parameter
4 MHz Oscillator Variable Oscillator
UnitMin Max Min Max
01/t
CLCL Oscillator Frequency 0.0 16 MHz
10 tRLDV Read Low to Data Valid 325 3.0tCLCL-50 ns
12 tRLRH RD Pulse Width 365 3.0tCLCL-10 ns
14 tWHDX Data Hold After WR High 240 2.0tCLCL-10 ns
15 tDVWH Data Valid to WR High 375 3.0tCLCL ns
16 tWLWH WR Pulse Width 365 3.0tCLCL-10 ns
Table 118. External Data Memory Characteristics, 2.7 - 5.5 Volts, no Wait-state
Symbol Parameter
4 MHz Oscillator Variable Oscillator
UnitMin Max Min Max
01/t
CLCL Oscillator Frequency 0.0 8 MHz
1t
LHLL ALE Pulse Width 235 tCLCL-15 ns
2t
AVLL Address Valid A to ALE Low 115 0.5tCLCL-10(1) ns
3a tLLAX_ST
Address Hold After ALE Low,
write access 55
ns
3b tLLAX_LD
Address Hold after ALE Low,
read access 55
ns
4t
AVLLC Address Valid C to ALE Low 115 0.5tCLCL-10(1) ns
5t
AVRL Address Valid to RD Low 235 1.0tCLCL-15 ns
6t
AVWL Address Valid to WR Low 235 1.0tCLCL-15 ns
7t
LLWL ALE Low to WR Low 115 130 0.5tCLCL-10(2) 0.5tCLCL+5(2) ns
8t
LLRL ALE Low to RD Low 115 130 0.5tCLCL-10(2) 0.5tCLCL+5(2) ns
9t
DVRH Data Setup to RD High 45 45 ns
10 tRLDV Read Low to Data Valid 190 1.0tCLCL-60 ns
11 tRHDX Data Hold After RD High 0 0 ns
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ATmega162/V
Notes: 1. This assumes 50% clock duty cycle. The half period is actually the high time of the external clock, XTAL1.
2. This assumes 50% clock duty cycle. The half period is actually the low time of the external clock, XTAL1.
12 tRLRH RD Pulse Width 235 1.0tCLCL-15 ns
13 tDVWL Data Setup to WR Low 105 0.5tCLCL-20(1) ns
14 tWHDX Data Hold After WR High 235 1.0tCLCL-15 ns
15 tDVWH Data Valid to WR High 250 1.0tCLCL ns
16 tWLWH WR Pulse Width 235 1.0tCLCL-15 ns
Table 118. External Data Memory Characteristics, 2.7 - 5.5 Volts, no Wait-state (Continued)
Symbol Parameter
4 MHz Oscillator Variable Oscillator
UnitMin Max Min Max
Table 119. External Data Memory Characteristics, 2.7 - 5.5 Volts, SRWn1 = 0, SRWn0 = 1
Symbol Parameter
4 MHz Oscillator Variable Oscillator
UnitMin Max Min Max
01/t
CLCL Oscillator Frequency 0.0 8 MHz
10 tRLDV Read Low to Data Valid 440 2.0tCLCL-60 ns
12 tRLRH RD Pulse Width 485 2.0tCLCL-15 ns
15 tDVWH Data Valid to WR High 500 2.0tCLCL ns
16 tWLWH WR Pulse Width 485 2.0tCLCL-15 ns
Table 120. External Data Memory Characteristics, 2.7 - 5.5 Volts, SRWn1 = 1, SRWn0 = 0
Symbol Parameter
4 MHz Oscillator Variable Oscillator
UnitMin Max Min Max
01/t
CLCL Oscillator Frequency 0.0 8 MHz
10 tRLDV Read Low to Data Valid 690 3.0tCLCL-60 ns
12 tRLRH RD Pulse Width 735 3.0tCLCL-15 ns
15 tDVWH Data Valid to WR High 750 3.0tCLCL ns
16 tWLWH WR Pulse Width 735 3.0tCLCL-15 ns
Table 121. External Data Memory Characteristics, 2.7 - 5.5 Volts, SRWn1 = 1, SRWn0 = 1
Symbol Parameter
4 MHz Oscillator Variable Oscillator
UnitMin Max Min Max
01/t
CLCL Oscillator Frequency 0.0 8 MHz
10 tRLDV Read Low to Data Valid 690 3.0tCLCL-60 ns
12 tRLRH RD Pulse Width 735 3.0tCLCL-15 ns
14 tWHDX Data Hold After WR High 485 2.0tCLCL-15 ns
15 tDVWH Data Valid to WR High 750 3.0tCLCL ns
16 tWLWH WR Pulse Width 735 3.0tCLCL-15 ns
273
2513K–AVR–07/09
ATmega162/V
Figure 118. External Memory Timing (SRWn1 = 0, SRWn0 = 0
Figure 119. External Memory Timing (SRWn1 = 0, SRWn0 = 1)
ALE
T1 T2 T3
Write
Read
WR
T4
A15:8
AddressPrev. addr.
DA7:0
Address DataPrev. data XX
RD
DA7:0 (XMBK = 0)
DataAddress
System Clock (CLK
CPU
)
1
4
2
7
6
3a
3b
5
8 12
16
13
10
11
14
15
9
ALE
T1 T2 T3
Write
Read
WR
T5
A15:8 AddressPrev. addr.
DA7:0 Address Data
Prev. data XX
RD
DA7:0 (XMBK = 0) DataAddress
System Clock (CLKCPU)
1
4
2
7
6
3a
3b
5
8 12
16
13
10
11
14
15
9
T4
274
2513K–AVR–07/09
ATmega162/V
Figure 120. External Memory Timing (SRWn1 = 1, SRWn0 = 0)
Figure 121. External Memory Timing (SRWn1 = 1, SRWn0 = 1)(1)
Note: 1. The ALE pulse in the last period (T4 - T7) is only present if the next instruction accesses the
RAM (internal or external).
ALE
T1 T2 T3
Write
Read
WR
T6
A15:8 Address
Prev. addr.
DA7:0 Address DataPrev. data XX
RD
DA7:0 (XMBK = 0) Data
Address
System Clock (CLK
CPU
)
1
4
2
7
6
3a
3b
5
812
16
13
10
11
14
15
9
T4 T5
ALE
T1 T2 T3
Write
Read
WR
T7
A15:8 Address
Prev. addr.
DA7:0 Address DataPrev. data XX
RD
DA7:0 (XMBK = 0) Data
Address
System Clock (CLK
CPU
)
1
4
2
7
6
3a
3b
5
8 12
16
13
10
11
14
15
9
T4 T5 T6
275
2513K–AVR–07/09
ATmega162/V
ATmega162
Typical
Characteristics
The following charts show typical behavior. These figures are not tested during manufacturing.
All current consumption measurements are performed with all I/O pins configured as inputs and
with internal pull-ups enabled. A sine wave generator with rail-to-rail output is used as clock
source. The CKSEL Fuses are programmed to select external clock.
The power consumption in Power-down mode is independent of clock selection.
The current consumption is a function of several factors such as: Operating voltage, operating
frequency, loading of I/O pins, switching rate of I/O pins, code executed and ambient tempera-
ture. The dominating factors are operating voltage and frequency.
The current drawn from capacitive loaded pins may be estimated (for one pin) as CL*VCC*f where
CL = load capacitance, VCC = operating voltage and f = average switching frequency of I/O pin.
The parts are characterized at frequencies higher than test limits. Parts are not guaranteed to
function properly at frequencies higher than the ordering code indicates.
The difference between current consumption in Power-down mode with Watchdog Timer
enabled and Power-down mode with Watchdog Timer disabled represents the differential cur-
rent drawn by the Watchdog Timer.
Active Supply Current Figure 122. Active Supply Current vs. Frequency (0.1 - 1.0 MHz)
ACTIVE SUPPLY CURRENT vs. FREQUENCY
0.1 - 1.0 MHz
0
0.5
1
1.5
2
2.5
3
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Frequency (MHz)
ICC (mA)
5.5V
4.5V
4.0V
3.3V
2.7V
1.8V
5.0V
276
2513K–AVR–07/09
ATmega162/V
Figure 123. Active Supply Current vs. Frequency (1 - 20 MHz)
Figure 124. Active Supply Current vs. VCC (Internal RC Oscillator, 8 MHz)
ACTIVE SUPPLY CURRENT vs. FREQUENCY
1- 20 MHz
0
5
10
15
20
25
30
35
40
45
02468101214161820
Frequency (MHz)
ICC (mA)
5.5V
4.5V
4.0V
3.3V
2.7V
1.8V
5.0V
ACTIVE SUPPLY CURRENT vs. V
CC
INTERNAL RC OSCILLATOR, 8 MHz
0
2
4
6
8
10
12
14
16
18
20
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(mA)
85°C
25°C
-40°C
277
2513K–AVR–07/09
ATmega162/V
Figure 125. Active Supply Current vs. VCC (32 kHz External Oscillator)
Idle Supply Current Figure 126. Idle Supply Current vs. Frequency (0.1 - 1.0 MHz)
ACTIVE SUPPLY CURRENT vs. V
CC
32kHz EXTERNAL OSCILLATOR
0
50
100
150
200
250
300
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
25°C
85°C
IDLE SUPPLY CURRENT vs. FREQUENCY
0.1 - 1.0 MHz
0
0.2
0.4
0.6
0.8
1
1.2
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Frequency (MHz)
ICC (mA)
5.5V
4.5V
4.0V
3.3V
2.7V
1.8V
5.0V
278
2513K–AVR–07/09
ATmega162/V
Figure 127. Idle Supply Current vs. Frequency (1 - 20 MHz)
Figure 128. Idle Supply Current vs. VCC (Internal RC Oscillator, 8 MHz)
IDLE SUPPLY CURRENT vs. FREQUENCY
1 - 20 MHz
0
5
10
15
20
25
0 2 4 6 8 10 12 14 16 18 20
Frequency (MHz)
I
CC
(mA)
5.5V
4.5V
4.0V
3.3V
2.7V
1.8V
5.0V
IDLE SUPPLY CURRENT vs. V
CC
INTERNAL RC OSCILLATOR, 8 MHz
0
1
2
3
4
5
6
7
8
9
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
ICC (mA)
85°C
25°C
-40°C
279
2513K–AVR–07/09
ATmega162/V
Figure 129. Idle Supply Current vs. VCC (32 kHz External Oscillator)
Power-down Supply
Current
Figure 130. Power-down Supply Current vs. VCC (Watchdog Timer Disabled)
IDLE SUPPLY CURRENT vs. V
CC
32kHz EXTERNAL OSCILLATOR
0
10
20
30
40
50
60
70
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
85°C
25°C
POWER-DOWN SUPPLY CURRENT vs. VCC
WATCHDOG TIMER DISABLED
0
0.5
1
1.5
2
2.5
3
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
85°C
25°C
-40°C
280
2513K–AVR–07/09
ATmega162/V
Figure 131. Power-down Supply Current vs. VCC (Watchdog Timer Enabled)
Power-save Supply
Current
Figure 132. Power-save Supply Current vs. VCC (Watchdog Timer Disabled)
POWER-DOWN SUPPLY CURRENT vs. V
CC
WATCHDOG TIMER ENABLED
0
5
10
15
20
25
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
85°C
25°C
-40°C
POWER-SAVE SUPPLY CURRENT vs. V
CC
WATCHDOG TIMER DISABLED
0
5
10
15
20
25
30
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
85°C
25°C
281
2513K–AVR–07/09
ATmega162/V
Standby Supply
Current
Figure 133. Standby Supply Current vs. VCC (455 kHz Resonator, Watchdog Timer Disabled)
Figure 134. Standby Supply Current vs. VCC (1 MHz Resonator, Watchdog Timer Disabled)
STANDBY SUPPLY CURRENT vs. V
CC
455 kHz RESONATOR, WATCHDOG TIMER DISABLED
0
10
20
30
40
50
60
70
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
STANDBY SUPPLY CURRENT vs. V
CC
1 MHz RESONATOR, WATCHDOG TIMER DISABLED
0
10
20
30
40
50
60
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
282
2513K–AVR–07/09
ATmega162/V
Figure 135. Standby Supply Current vs. VCC (2 MHz Resonator, Watchdog Timer Disabled)
Figure 136. Standby Supply Current vs. VCC (2 MHz Xtal, Watchdog Timer Disabled)
STANDBY SUPPLY CURRENT vs. VCC
2 MHz XTAL, WATCHDOG TIMER DISABLED
0
10
20
30
40
50
60
70
80
90
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
STANDBY SUPPLY CURRENT vs. VCC
2 MHz XTAL, WATCHDOG TIMER DISABLED
0
10
20
30
40
50
60
70
80
90
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
283
2513K–AVR–07/09
ATmega162/V
Figure 137. Standby Supply Current vs. VCC (4 MHz Resonator, Watchdog Timer Disabled)
Figure 138. Standby Supply Current vs. VCC (4 MHz Xtal, Watchdog Timer Disabled)
STANDBY SUPPLY CURRENT vs. V
CC
4 MHz RESONATOR, WATCHDOG TIMER DISABLED
0
20
40
60
80
100
120
140
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
STANDBY SUPPLY CURRENT vs. V
CC
4 MHz XTAL, WATCHDOG TIMER DISABLED
0
20
40
60
80
100
120
140
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
284
2513K–AVR–07/09
ATmega162/V
Figure 139. Standby Supply Current vs. VCC (6 MHz Resonator, Watchdog Timer Disabled)
Figure 140. Standby Supply Current vs. VCC (6 MHz Xtal, Watchdog Timer Disabled)
STANDBY SUPPLY CURRENT vs. V
CC
6 MHz RESONATOR, WATCHDOG TIMER DISABLED
0
20
40
60
80
100
120
140
160
180
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
STANDBY SUPPLY CURRENT vs. V
CC
6 MHz XTAL, WATCHDOG TIMER DISABLED
0
20
40
60
80
100
120
140
160
180
200
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
285
2513K–AVR–07/09
ATmega162/V
Pin Pull-up Figure 141. I/O Pin Pull-up Resistor Current vs. Input Voltage (VCC = 5V)
Figure 142. I/O Pin Pull-up Resistor Current vs. Input Voltage (VCC = 2.7V)
I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
Vcc = 5V
0
20
40
60
80
100
120
140
160
012345
V
IO
(V)
I
IO
(uA)
85°C
25°C
-40°C
6
I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
Vcc = 2.7V
0
10
20
30
40
50
60
70
80
0 0.5 1 1.5 2 2.5 3
V
IO
(V)
I
IO
(uA)
85°C 25°C
-40°C
286
2513K–AVR–07/09
ATmega162/V
Figure 143. I/O Pin Pull-up Resistor Current vs. Input Voltage (VCC = 1.8V)
Figure 144. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 5V)
I/O PIN PULL-UP RESISTOR CURRENT vs. INPUT VOLTAGE
Vcc = 1.8V
0
10
20
30
40
50
60
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
V
OP
(V)
I
OP
(uA)
85°C 25°C
-40°C
RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE
Vcc = 5V
0
20
40
60
80
100
120
012345
V
RESET
(V)
I
RESET
(uA)
-40°C
25°C
85°C
6
287
2513K–AVR–07/09
ATmega162/V
Figure 145. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 2.7V)
Figure 146. Reset Pull-up Resistor Current vs. Reset Pin Voltage (VCC = 1.8V)
RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE
Vcc = 2.7V
0
10
20
30
40
50
60
0 0.5 1 1.5 2 2.5 3
V
RESET
(V)
I
RESET
(uA)
-40°C
25°C
85°C
RESET PULL-UP RESISTOR CURRENT vs. RESET PIN VOLTAGE
Vcc = 1.8V
0
5
10
15
20
25
30
35
40
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
V
RESET
(V)
I
RESET
(uA)
-40°C
25°C
85°C
288
2513K–AVR–07/09
ATmega162/V
Pin Driver Strength Figure 147. I/O Pin Source Current vs. Output Voltage (VCC = 5V)
Figure 148. I/O Pin Source Current vs. Output Voltage (VCC = 2.7V)
I/O PIN SOURCE CURRENT vs. OUTPUT VOLTAGE
Vcc = 5V
0
10
20
30
40
50
60
70
80
90
012345
V
OH
(V)
I
OH
(mA)
85°C
25°C
-40°C
6
I/O PIN SOURCE CURRENT vs. OUTPUT VOLTAGE
Vcc = 2.7V
0
5
10
15
20
25
30
0 0.5 1 1.5 2 2.5 3
V
OH
(V)
I
OH
(mA)
85°C
25°C
-40°C
289
2513K–AVR–07/09
ATmega162/V
Figure 149. I/O Pin Source Current vs. Output Voltage (VCC = 1.8V)
Figure 150. I/O Pin Sink Current vs. Output Voltage (VCC = 5V)
I/O PIN SOURCE CURRENT vs. OUTPUT VOLTAGE
Vcc = 1.8V
0
1
2
3
4
5
6
7
8
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
V
OH
(V)
I
OH
(mA)
85°C
25°C
-40°C
I/O PIN SINK CURRENT vs. OUTPUT VOLTAGE
Vcc = 5V
0
10
20
30
40
50
60
70
80
90
0 0.5 1 1.5 2 2.5
V
OL
(V)
I
OL
(mA)
85°C
25°C
-40°C
290
2513K–AVR–07/09
ATmega162/V
Figure 151. I/O Pin Sink Current vs. Output Voltage (VCC = 2.7V)
Figure 152. I/O Pin Sink Current vs. Output Voltage (VCC = 1.8V)
I/O PIN SINK CURRENT vs. OUTPUT VOLTAGE
Vcc = 2.7V
0
5
10
15
20
25
30
35
0 0.5 1 1.5 2 2.5
V
OL
(V)
I
OL
(mA)
85°C
25°C
-40°C
I/O PIN SINK CURRENT vs. OUTPUT VOLTAGE
Vcc = 1.8V
0
2
4
6
8
10
12
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
V
OL
(V)
I
OL
(mA)
85°C
25°C
-40°C
291
2513K–AVR–07/09
ATmega162/V
Pin Thresholds and
Hysteresis
Figure 153. I/O Pin Input Threshold Voltage vs. VCC (VIH, I/O Pin Read as “1”)
Figure 154. I/O Pin Input Threshold Voltage vs. VCC (VIL, I/O Pin Read as “0”)
I/O PIN INPUT THRESHOLD VOLTAGE vs. V
CC
VIH, I/O PIN READ AS '1'
0
0.5
1
1.5
2
2.5
3
1.522.533.544.555.5
V
CC
(V)
Threshold (V)
85°C
25°C
-40°C
I/O PIN INPUT THRESHOLD VOLTAGE vs. V
CC
VIL, I/O PIN READ AS '0'
0
0.5
1
1.5
2
2.5
3
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
Threshold (V)
85°C
25°C
-40°C
292
2513K–AVR–07/09
ATmega162/V
Figure 155. I/O Pin Input Hysteresis vs. VCC
Figure 156. Reset Input Threshold Voltage vs. VCC (VIH, Reset Pin Read as “1”)
I/O PIN INPUT HYSTERESIS vs. V
CC
0
0.1
0.2
0.3
0.4
0.5
0.6
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
Threshold (V)
85°C
25°C
-40°C
RESET INPUT THRESHOLD VOLTAGE vs. V
CC
VIH, RESET PIN READ AS '1'
0
0.5
1
1.5
2
2.5
3
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
Threshold (V)
85°C
25°C
-40°C
293
2513K–AVR–07/09
ATmega162/V
Figure 157. Reset Input Threshold Voltage vs. VCC (VIL, Reset Pin Read as “0”)
Figure 158. Reset Input Pin Hysteresis vs. VCC
RESET INPUT THRESHOLD VOLTAGE vs. V
CC
VIL, RESET PIN READ AS '0'
0
0.5
1
1.5
2
2.5
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
Threshold (V)
85°C
25°C
-40°C
RESET INPUT PIN HYSTERESIS vs. VCC
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC (V)
Threshold (V)
85°C
25°C
-40°C
294
2513K–AVR–07/09
ATmega162/V
BOD Thresholds and
Analog Comparator
Offset
Figure 159. BOD Thresholds vs. Temperature (BOD Level is 4.3V)
Figure 160. BOD Thresholds vs. Temperature (BOD Level is 2.7V)
BOD THRESHOLDS vs. TEMPERATURE
BODLEVEL IS 4.3V
4
4.1
4.2
4.3
4.4
4.5
4.6
-50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100
Temperature (˚C)
Threshold (V)
Rising V
CC
Falling V
CC
BOD THRESHOLDS vs. TEMPERATURE
BODLEVEL IS 2.7V
2.4
2.5
2.6
2.7
2.8
2.9
3
-50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100
Temperature (˚C)
Threshold (V)
Rising V
CC
Falling V
CC
295
2513K–AVR–07/09
ATmega162/V
Figure 161. BOD Thresholds vs. Temperature (BOD Level is 2.3V)
Figure 162. BOD Thresholds vs. Temperature (BOD Level is 1.8V)
BOD THRESHOLDS vs. TEMPERATURE
BODLEVEL IS 2.3V
2
2.1
2.2
2.3
2.4
2.5
2.6
-50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100
Temperature (˚C)
Threshold (V)
Rising V
CC
Falling V
CC
BOD THRESHOLDS vs. TEMPERATURE
BODLEVEL IS 1.8V
1.5
1.6
1.7
1.8
1.9
2
2.1
-50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100
Temperature (˚C)
Threshold (V)
Rising V
CC
Falling V
CC
296
2513K–AVR–07/09
ATmega162/V
Figure 163. Bandgap Voltage vs. VCC
Figure 164. Analog Comparator Offset Voltage vs. Common Mode Voltage (VCC = 5V)
BANDGAP VOLTAGE vs. VCC
1.08
1.09
1.1
1.11
1.12
1.13
1.14
1.5 2 2.5 3 3.5 4 4.5 5 5.5
Vcc (V)
Bandgap Voltage (V)
85°C
25°C
-40°C
ANALOG COMPARATOR OFFSET VOLTAGE vs. COMMON MODE VOLTAGE
V
CC
= 5V
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0.01
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Common Mode Voltage (V)
Comparator Offset Voltage (V)
85°C
25°C
-40°C
297
2513K–AVR–07/09
ATmega162/V
Figure 165. Analog Comparator Offset Voltage vs. Common Mode Voltage (VCC =2.7V)
Internal Oscillator
Speed
Figure 166. Watchdog Oscillator Frequency vs. VCC
ANALOG COMPARATOR OFFSET VOLTAGE vs. COMMON MODE VOLTAGE
V
CC
= 2.7V
-0.001
0
0.001
0.002
0.003
0.004
0.005
0.006
0 0.5 1 1.5 2 2.5 3
Common Mode Voltage (V)
Comparator Offset Voltage (V)
85°C
25°C
-40°C
WATCHDOG OSCILLATOR FREQUENCY vs. V
CC
1000
1050
1100
1150
1200
1250
1300
1.5 2 2.5 3 3.5 4 4.5 5 5.5
VCC (V)
FRC (kHz)
85°C
25°C
-40°C
298
2513K–AVR–07/09
ATmega162/V
Figure 167. Calibrated 8 MHz RC Oscillator Frequency vs. Temperature
Figure 168. Calibrated 8 MHz RC Oscillator Frequency vs.VCC
CALIBRATED 8MHz RC OSCILLATOR FREQUENCY vs. TEMPERATURE
7.5
7.6
7.7
7.8
7.9
8
8.1
8.2
8.3
8.4
-60 -40 -20 0 20 40 60 80 100
T
a
(˚C)
F
RC
(MHz)
4.0V
1.8V
5.5V
2.7V
CALIBRATED 8MHz RC OSCILLATOR FREQUENCY vs. VCC
6
6.5
7
7.5
8
8.5
9
9.5
10
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
F
RC
(MHz)
85
°C
25
°C
-40
°C
299
2513K–AVR–07/09
ATmega162/V
Figure 169. Calibrated 8 MHz RC Oscillator Frequency vs. Osccal Value
Current Consumption
of Peripheral Units
Figure 170. Brownout Detector Current vs. VCC
CALIBRATED 8MHz RC OSCILLATOR FREQUENCY vs. OSCCAL VALUE
4
6
8
10
12
14
16
0 163248648096112
OSCCAL VALUE
F
RC
(MHz)
BROWNOUT DETECTOR CURRENT vs. V
CC
-5
0
5
10
15
20
25
30
35
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
25
°C
-40
°C
85
°C
300
2513K–AVR–07/09
ATmega162/V
Figure 171. 32 kHz TOSC Current vs. VCC (Watchdog Timer Disabled)
Figure 172. Watchdog TImer Current vs. VCC
32kHz TOSC CURRENT vs. V
CC
WATCHDOG TIMER DISABLED
0
5
10
15
20
25
30
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
85
°C
25
°C
WATCHDOG TIMER CURRENT vs. V
CC
0
2
4
6
8
10
12
14
16
18
20
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
85
°C
25
°C
-40
°C
301
2513K–AVR–07/09
ATmega162/V
Figure 173. Analog Comparator Current vs. VCC
Figure 174. Programming Current vs. VCC
ANALOG COMPARATOR CURRENT vs. V
CC
0
10
20
30
40
50
60
70
80
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(uA)
85
°C
25
°C
-40
°C
PROGRAMMING CURRENT vs. Vcc
0
5
10
15
20
25
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
I
CC
(mA)
85°C
25°C
-40°C
302
2513K–AVR–07/09
ATmega162/V
Current Consumption
in Reset and Reset
Pulsewidth
Figure 175. Reset Supply Current vs. Frequency (0.1 - 1.0 MHz, Excluding Current Through
The Reset Pull-up)
Figure 176. Reset Supply Current vs. Frequency (1 - 20 MHz, Excluding Current Through The
Reset Pull-up)
RESET SUPPLY CURRENT vs. FREQUENCY
0.1 - 1.0 MHz, EXCLUDING CURRENT THROUGH THE RESET PULLUP
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Frequency (MHz)
I
CC
(mA)
5.5V
4.5V
4.0V
3.3V
2.7V
1.8V
5.0V
RESET SUPPLY CURRENT vs. FREQUENCY
1 - 20 MHz, EXCLUDING CURRENT THROUGH THE RESET PULLUP
0
5
10
15
20
25
30
35
02468101214161820
Frequency (MHz)
I
CC
(mA)
5.5V
4.5V
4.0V
3.3V
2.7V
1.8V
5.0V
303
2513K–AVR–07/09
ATmega162/V
Figure 177. Reset Pulse Width vs. VCC
RESET PULSE WIDTH vs. V
CC
0
500
1000
1500
2000
2500
1.5 2 2.5 3 3.5 4 4.5 5 5.5
V
CC
(V)
Pulsewidth (ns)
85
°C
25
°C
-40
°C
304
2513K–AVR–07/09
ATmega162/V
Register Summary
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
(0xFF) Reserved – – – – – – – –
.. Reserved – – – – – – – –
(0x9E) Reserved – – – – – – – –
(0x9D) Reserved – – – – – – – –
(0x9C) Reserved – – – – – – – –
(0x9B) Reserved – – – – – – – –
(0x9A) Reserved – – – – – – – –
(0x99) Reserved – – – – – – – –
(0x98) Reserved – – – – – – – –
(0x97) Reserved – – – – – – – –
(0x96) Reserved – – – – – – – –
(0x95) Reserved – – – – – – – –
(0x94) Reserved – – – – – – – –
(0x93) Reserved – – – – – – – –
(0x92) Reserved – – – – – – – –
(0x91) Reserved – – – – – – – –
(0x90) Reserved – – – – – – – –
(0x8F) Reserved – – – – – – – –
(0x8E) Reserved – – – – – – – –
(0x8D) Reserved – – – – – – – –
(0x8C) Reserved – – – – – – – –
(0x8B) TCCR3A COM3A1 COM3A0 COM3B1 COM3B0 FOC3A FOC3B WGM31 WGM30 131
(0x8A) TCCR3B ICNC3 ICES3 – WGM33 WGM32 CS32 CS31 CS30 128
(0x89) TCNT3H Timer/Counter3 – Counter Register High Byte 133
(0x88) TCNT3L Timer/Counter3 – Counter Register Low Byte 133
(0x87) OCR3AH Timer/Counter3 – Output Compare Register A High Byte 133
(0x86) OCR3AL Timer/Counter3 – Output Compare Register A Low Byte 133
(0x85) OCR3BH Timer/Counter3 – Output Compare Register B High Byte 133
(0x84) OCR3BL Timer/Counter3 – Output Compare Register B Low Byte 133
(0x83) Reserved – – – – – – – –
(0x82) Reserved – – – – – – – –
(0x81) ICR3H Timer/Counter3 – Input Capture Register High Byte 134
(0x80) ICR3L Timer/Counter3 – Input Capture Register Low Byte 134
(0x7F) Reserved – – – – – – – –
(0x7E) Reserved – – – – – – – –
(0x7D) ETIMSK –– TICIE3 OCIE3A OCIE3B TOIE3 – – 135
(0x7C) ETIFR –– ICF3 OCF3A OCF3B TOV3 – – 135
(0x7B) Reserved – – – – – – – –
(0x7A) Reserved – – – – – – – –
(0x79) Reserved – – – – – – – –
(0x78) Reserved – – – – – – – –
(0x77) Reserved – – – – – – – –
(0x76) Reserved – – – – – – – –
(0x75) Reserved – – – – – – – –
(0x74) Reserved – – – – – – – –
(0x73) Reserved – – – – – – – –
(0x72) Reserved – – – – – – – –
(0x71) Reserved – – – – – – – –
(0x70) Reserved – – – – – – – –
(0x6F) Reserved – – – – – – – –
(0x6E) Reserved – – – – – – – –
(0x6D) Reserved – – – – – – – –
(0x6C) PCMSK1 PCINT15 PCINT14 PCINT13 PCINT12 PCINT11 PCINT10 PCINT9 PCINT8 88
(0x6B) PCMSK0 PCINT7 PCINT6 PCINT5 PCINT4 PCINT3 PCINT2 PCINT1 PCINT0 88
(0x6A) Reserved – – – – – – – –
(0x69) Reserved – – – – – – – –
(0x68) Reserved – – – – – – – –
(0x67) Reserved – – – – – – – –
(0x66) Reserved – – – – – – – –
(0x65) Reserved – – – – – – – –
(0x64) Reserved – – – – – – – –
(0x63) Reserved – – – – – – – –
(0x62) Reserved – – – – – – – –
(0x61) CLKPR CLKPCE ––– CLKPS3 CLKPS2 CLKPS1 CLKPS0 41
305
2513K–AVR–07/09
ATmega162/V
(0x60) Reserved – – – – – – – –
0x3F (0x5F) SREG I T H S V N Z C 10
0x3E (0x5E) SPH SP15 SP14 SP13 SP12 SP11 SP10 SP9 SP8 13
0x3D (0x5D) SPL SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 13
0x3C(2)(0x5C)(2) UBRR1H URSEL1 UBRR1[11:8] 190
UCSR1C URSEL1 UMSEL1 UPM11 UPM10 USBS1 UCSZ11 UCSZ10 UCPOL1 189
0x3B (0x5B) GICR INT1 INT0 INT2 PCIE1 PCIE0 – IVSEL IVCE 61, 86
0x3A (0x5A) GIFR INTF1 INTF0 INTF2 PCIF1 PCIF0 – – – 87
0x39 (0x59) TIMSK TOIE1 OCIE1A OCIE1B OCIE2 TICIE1 TOIE2 TOIE0 OCIE0 102, 134, 154
0x38 (0x58) TIFR TOV1 OCF1A OCF1B OCF2 ICF1 TOV2 TOV0 OCF0 103, 135, 155
0x37 (0x57) SPMCR SPMIE RWWSB – RWWSRE BLBSET PGWRT PGERS SPMEN 221
0x36 (0x56) EMCUCR SM0 SRL2 SRL1 SRL0 SRW01 SRW00 SRW11 ISC2 30,44,85
0x35 (0x55) MCUCR SRE SRW10 SE SM1 ISC11 ISC10 ISC01 ISC00 30,43,84
0x34 (0x54) MCUCSR JTD – SM2 JTRF WDRF BORF EXTRF PORF 43,51,207
0x33 (0x53) TCCR0 FOC0 WGM00 COM01 COM00 WGM01 CS02 CS01 CS00 100
0x32 (0x52) TCNT0 Timer/Counter0 (8 Bits) 102
0x31 (0x51) OCR0 Timer/Counter0 Output Compare Register 102
0x30 (0x50) SFIOR TSM XMBK XMM2 XMM1 XMM0 PUD PSR2 PSR310 32,70,105,156
0x2F (0x4F) TCCR1A COM1A1 COM1A0 COM1B1 COM1B0 FOC1A FOC1B WGM11 WGM10 128
0x2E (0x4E) TCCR1B ICNC1 ICES1 – WGM13 WGM12 CS12 CS11 CS10 131
0x2D (0x4D) TCNT1H Timer/Counter1 – Counter Register High Byte 133
0x2C (0x4C) TCNT1L Timer/Counter1 – Counter Register Low Byte 133
0x2B (0x4B) OCR1AH Timer/Counter1 – Output Compare Register A High Byte 133
0x2A (0x4A) OCR1AL Timer/Counter1 – Output Compare Register A Low Byte 133
0x29 (0x49) OCR1BH Timer/Counter1 – Output Compare Register B High Byte 133
0x28 (0x48) OCR1BL Timer/Counter1 – Output Compare Register B Low Byte 133
0x27 (0x47) TCCR2 FOC2 WGM20 COM21 COM20 WGM21 CS22 CS21 CS20 149
0x26 (0x46) ASSR –––– AS2 TCN2UB OCR2UB TCR2UB 152
0x25 (0x45) ICR1H Timer/Counter1 – Input Capture Register High Byte 134
0x24 (0x44) ICR1L Timer/Counter1 – Input Capture Register Low Byte 134
0x23 (0x43) TCNT2 Timer/Counter2 (8 Bits) 151
0x22 (0x42) OCR2 Timer/Counter2 Output Compare Register 151
0x21 (0x41) WDTCR – – – WDCE WDE WDP2 WDP1 WDP0 53
0x20(2) (0x40)(2) UBRR0H URSEL0 ––– UBRR0[11:8] 190
UCSR0C URSEL0 UMSEL0 UPM01 UPM00 USBS0 UCSZ01 UCSZ00 UCPOL0 189
0x1F (0x3F) EEARH – – – – – – –EEAR8 20
0x1E (0x3E) EEARL EEPROM Address Register Low Byte 20
0x1D (0x3D) EEDR EEPROM Data Register 21
0x1C (0x3C) EECR –––– EERIE EEMWE EEWE EERE 21
0x1B (0x3B) PORTA PORTA7 PORTA6 PORTA5 PORTA4 PORTA3 PORTA2 PORTA1 PORTA0 82
0x1A (0x3A) DDRA DDA7 DDA6 DDA5 DDA4 DDA3 DDA2 DDA1 DDA0 82
0x19 (0x39) PINA PINA7 PINA6 PINA5 PINA4 PINA3 PINA2 PINA1 PINA0 82
0x18 (0x38) PORTB PORTB7 PORTB6 PORTB5 PORTB4 PORTB3 PORTB2 PORTB1 PORTB0 82
0x17 (0x37) DDRB DDB7 DDB6 DDB5 DDB4 DDB3 DDB2 DDB1 DDB0 82
0x16 (0x36) PINB PINB7 PINB6 PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 82
0x15 (0x35) PORTC PORTC7 PORTC6 PORTC5 PORTC4 PORTC3 PORTC2 PORTC1 PORTC0 82
0x14 (0x34) DDRC DDC7 DDC6 DDC5 DDC4 DDC3 DDC2 DDC1 DDC0 82
0x13 (0x33) PINC PINC7 PINC6 PINC5 PINC4 PINC3 PINC2 PINC1 PINC0 83
0x12 (0x32) PORTD PORTD7 PORTD6 PORTD5 PORTD4 PORTD3 PORTD2 PORTD1 PORTD0 83
0x11 (0x31) DDRD DDD7 DDD6 DDD5 DDD4 DDD3 DDD2 DDD1 DDD0 83
0x10 (0x30) PIND PIND7 PIND6 PIND5 PIND4 PIND3 PIND2 PIND1 PIND0 83
0x0F (0x2F) SPDR SPI Data Register 164
0x0E (0x2E) SPSR SPIF WCOL – – – – –SPI2X 164
0x0D (0x2D) SPCR SPIE SPE DORD MSTR CPOL CPHA SPR1 SPR0 162
0x0C (0x2C) UDR0 USART0 I/O Data Register 186
0x0B (0x2B) UCSR0A RXC0 TXC0 UDRE0 FE0 DOR0 UPE0 U2X0 MPCM0 186
0x0A (0x2A) UCSR0B RXCIE0 TXCIE0 UDRIE0 RXEN0 TXEN0 UCSZ02 RXB80 TXB80 187
0x09 (0x29) UBRR0L USART0 Baud Rate Register Low Byte 190
0x08 (0x28) ACSR ACD ACBG ACO ACI ACIE ACIC ACIS1 ACIS0 195
0x07 (0x27) PORTE – – – – – PORTE2 PORTE1 PORTE0 83
0x06 (0x26) DDRE – – – – – DDE2 DDE1 DDE0 83
0x05 (0x25) PINE – – – – – PINE2 PINE1 PINE0 83
0x04(1) (0x24)(1) OSCCAL – CAL6 CAL5 CAL4 CAL3 CAL2 CAL1 CAL0 39
OCDR On-chip Debug Register 202
0x03 (0x23) UDR1 USART1 I/O Data Register 186
0x02 (0x22) UCSR1A RXC1 TXC1 UDRE1 FE1 DOR1 UPE1 U2X1 MPCM1 186
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
306
2513K–AVR–07/09
ATmega162/V
Notes: 1. When the OCDEN Fuse is unprogrammed, the OSCCAL Register is always accessed on this address. Refer to the debug-
ger specific documentation for details on how to use the OCDR Register.
2. Refer to the USART description for details on how to access UBRRH and UCSRC.
3. For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory addresses
should never be written.
4. Some of the Status Flags are cleared by writing a logical one to them. Note that the CBI and SBI instructions will operate on
all bits in the I/O Register, writing a one back into any flag read as set, thus clearing the flag. The CBI and SBI instructions
work with registers 0x00 to 0x1F only.
0x01 (0x21) UCSR1B RXCIE1 TXCIE1 UDRIE1 RXEN1 TXEN1 UCSZ12 RXB81 TXB81 187
0x00 (0x20) UBRR1L USART1 Baud Rate Register Low Byte 190
Address Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Page
307
2513K–AVR–07/09
ATmega162/V
Instruction Set Summary
Mnemonics Operands Description Operation Flags #Clocks
ARITHMETIC AND LOGIC INSTRUCTIONS
ADD Rd, Rr Add two Registers Rd ← Rd + Rr Z,C,N,V,H 1
ADC Rd, Rr Add with Carry two Registers Rd ← Rd + Rr + C Z,C,N,V,H 1
ADIW Rdl,K Add Immediate to Word Rdh:Rdl ← Rdh:Rdl + K Z,C,N,V,S 2
SUB Rd, Rr Subtract two Registers Rd ← Rd - Rr Z,C,N,V,H 1
SUBI Rd, K Subtract Constant from Register Rd ← Rd - K Z,C,N,V,H 1
SBC Rd, Rr Subtract with Carry two Registers Rd ← Rd - Rr - C Z,C,N,V,H 1
SBCI Rd, K Subtract with Carry Constant from Reg. Rd ← Rd - K - C Z,C,N,V,H 1
SBIW Rdl,K Subtract Immediate from Word Rdh:Rdl ← Rdh:Rdl - K Z,C,N,V,S 2
AND Rd, Rr Logical AND Registers Rd ← Rd • Rr Z,N,V 1
ANDI Rd, K Logical AND Register and Constant Rd ← Rd • K Z,N,V 1
OR Rd, Rr Logical OR Registers Rd ← Rd v Rr Z,N,V 1
ORI Rd, K Logical OR Register and Constant Rd ← Rd v K Z,N,V 1
EOR Rd, Rr Exclusive OR Registers Rd ← Rd ⊕ Rr Z,N,V 1
COM Rd One’s Complement Rd ← 0xFF − Rd Z,C,N,V 1
NEG Rd Two’s Complement Rd ← 0x00 − Rd Z,C,N,V,H 1
SBR Rd,K Set Bit(s) in Register Rd ← Rd v K Z,N,V 1
CBR Rd,K Clear Bit(s) in Register Rd ← Rd • (0xFF - K) Z,N,V 1
INC Rd Increment Rd ← Rd + 1 Z,N,V 1
DEC Rd Decrement Rd ← Rd − 1 Z,N,V 1
TST Rd Test for Zero or Minus Rd ← Rd • Rd Z,N,V 1
CLR Rd Clear Register Rd ← Rd ⊕ Rd Z,N,V 1
SER Rd Set Register Rd ← 0xFF None 1
MUL Rd, Rr Multiply Unsigned R1:R0 ← Rd x Rr Z,C 2
MULS Rd, Rr Multiply Signed R1:R0 ← Rd x Rr Z,C 2
MULSU Rd, Rr Multiply Signed with Unsigned R1:R0 ← Rd x Rr Z,C 2
FMUL Rd, Rr Fractional Multiply Unsigned R1:R0 ← (Rd x Rr) << 1 Z,C 2
FMULS Rd, Rr Fractional Multiply Signed R1:R0 ← (Rd x Rr) << 1 Z,C 2
FMULSU Rd, Rr Fractional Multiply Signed with Unsigned R1:R0 ← (Rd x Rr) << 1 Z,C 2
BRANCH INSTRUCTIONS
RJMP k Relative Jump PC ← PC + k + 1 None 2
IJMP Indirect Jump to (Z) PC ← Z None 2
JMP k Direct Jump PC ← kNone3
RCALL k Relative Subroutine Call PC ← PC + k + 1 None 3
ICALL Indirect Call to (Z) PC ← ZNone3
CALL k Direct Subroutine Call PC ← kNone4
RET Subroutine Return PC ← STACK None 4
RETI Interrupt Return PC ← STACK I 4
CPSE Rd,Rr Compare, Skip if Equal if (Rd = Rr) PC ← PC + 2 or 3 None 1/2/3
CP Rd,Rr Compare Rd − Rr Z, N,V,C,H 1
CPC Rd,Rr Compare with Carry Rd − Rr − C Z, N,V,C,H 1
CPI Rd,K Compare Register with Immediate Rd − K Z, N,V,C,H 1
SBRC Rr, b Skip if Bit in Register Cleared if (Rr(b)=0) PC ← PC + 2 or 3 None 1/2/3
SBRS Rr, b Skip if Bit in Register is Set if (Rr(b)=1) PC ← PC + 2 or 3 None 1/2/3
SBIC P, b Skip if Bit in I/O Register Cleared if (P(b)=0) PC ← PC + 2 or 3 None 1/2/3
SBIS P, b Skip if Bit in I/O Register is Set if (P(b)=1) PC ← PC + 2 or 3 None 1/2/3
BRBS s, k Branch if Status Flag Set if (SREG(s) = 1) then PC←PC+k + 1 None 1/2
BRBC s, k Branch if Status Flag Cleared if (SREG(s) = 0) then PC←PC+k + 1 None 1/2
BREQ k Branch if Equal if (Z = 1) then PC ← PC + k + 1 None 1/2
BRNE k Branch if Not Equal if (Z = 0) then PC ← PC + k + 1 None 1/2
BRCS k Branch if Carry Set if (C = 1) then PC ← PC + k + 1 None 1/2
BRCC k Branch if Carry Cleared if (C = 0) then PC ← PC + k + 1 None 1/2
BRSH k Branch if Same or Higher if (C = 0) then PC ← PC + k + 1 None 1/2
BRLO k Branch if Lower if (C = 1) then PC ← PC + k + 1 None 1/2
BRMI k Branch if Minus if (N = 1) then PC ← PC + k + 1 None 1/2
BRPL k Branch if Plus if (N = 0) then PC ← PC + k + 1 None 1/2
BRGE k Branch if Greater or Equal, Signed if (N ⊕ V= 0) then PC ← PC + k + 1 None 1/2
BRLT k Branch if Less Than Zero, Signed if (N ⊕ V= 1) then PC ← PC + k + 1 None 1/2
BRHS k Branch if Half Carry Flag Set if (H = 1) then PC ← PC + k + 1 None 1/2
BRHC k Branch if Half Carry Flag Cleared if (H = 0) then PC ← PC + k + 1 None 1/2
BRTS k Branch if T Flag Set if (T = 1) then PC ← PC + k + 1 None 1/2
BRTC k Branch if T Flag Cleared if (T = 0) then PC ← PC + k + 1 None 1/2
BRVS k Branch if Overflow Flag is Set if (V = 1) then PC ← PC + k + 1 None 1/2
BRVC k Branch if Overflow Flag is Cleared if (V = 0) then PC ← PC + k + 1 None 1/2
308
2513K–AVR–07/09
ATmega162/V
BRIE k Branch if Interrupt Enabled if ( I = 1) then PC ← PC + k + 1 None 1/2
BRID k Branch if Interrupt Disabled if ( I = 0) then PC ← PC + k + 1 None 1/2
DATA TRANSFER INSTRUCTIONS
MOV Rd, Rr Move Between Registers Rd ← Rr None 1
MOVW Rd, Rr Copy Register Word Rd+1:Rd ← Rr+1:Rr None 1
LDI Rd, K Load Immediate Rd ← KNone1
LD Rd, X Load Indirect Rd ← (X) None 2
LD Rd, X+ Load Indirect and Post-Inc. Rd ← (X), X ← X + 1 None 2
LD Rd, - X Load Indirect and Pre-Dec. X ← X - 1, Rd ← (X) None 2
LD Rd, Y Load Indirect Rd ← (Y) None 2
LD Rd, Y+ Load Indirect and Post-Inc. Rd ← (Y), Y ← Y + 1 None 2
LD Rd, - Y Load Indirect and Pre-Dec. Y ← Y - 1, Rd ← (Y) None 2
LDD Rd,Y+q Load Indirect with Displacement Rd ← (Y + q) None 2
LD Rd, Z Load Indirect Rd ← (Z) None 2
LD Rd, Z+ Load Indirect and Post-Inc. Rd ← (Z), Z ← Z+1 None 2
LD Rd, -Z Load Indirect and Pre-Dec. Z ← Z - 1, Rd ← (Z) None 2
LDD Rd, Z+q Load Indirect with Displacement Rd ← (Z + q) None 2
LDS Rd, k Load Direct from SRAM Rd ← (k) None 2
ST X, Rr Store Indirect (X) ← Rr None 2
ST X+, Rr Store Indirect and Post-Inc. (X) ← Rr, X ← X + 1 None 2
ST - X, Rr Store Indirect and Pre-Dec. X ← X - 1, (X) ← Rr None 2
ST Y, Rr Store Indirect (Y) ← Rr None 2
ST Y+, Rr Store Indirect and Post-Inc. (Y) ← Rr, Y ← Y + 1 None 2
ST - Y, Rr Store Indirect and Pre-Dec. Y ← Y - 1, (Y) ← Rr None 2
STD Y+q,Rr Store Indirect with Displacement (Y + q) ← Rr None 2
ST Z, Rr Store Indirect (Z) ← Rr None 2
ST Z+, Rr Store Indirect and Post-Inc. (Z) ← Rr, Z ← Z + 1 None 2
ST -Z, Rr Store Indirect and Pre-Dec. Z ← Z - 1, (Z) ← Rr None 2
STD Z+q,Rr Store Indirect with Displacement (Z + q) ← Rr None 2
STS k, Rr Store Direct to SRAM (k) ← Rr None 2
LPM Load Program Memory R0 ← (Z) None 3
LPM Rd, Z Load Program Memory Rd ← (Z) None 3
LPM Rd, Z+ Load Program Memory and Post-Inc Rd ← (Z), Z ← Z+1 None 3
SPM Store Program Memory (Z) ← R1:R0 None -
IN Rd, P In Port Rd ← PNone1
OUT P, Rr Out Port P ← Rr None 1
PUSH Rr Push Register on Stack STACK ← Rr None 2
POP Rd Pop Register from Stack Rd ← STACK None 2
BIT AND BIT-TEST INSTRUCTIONS
SBI P,b Set Bit in I/O Register I/O(P,b) ← 1None2
CBI P,b Clear Bit in I/O Register I/O(P,b) ← 0None2
LSL Rd Logical Shift Left Rd(n+1) ← Rd(n), Rd(0) ← 0 Z,C,N,V 1
LSR Rd Logical Shift Right Rd(n) ← Rd(n+1), Rd(7) ← 0 Z,C,N,V 1
ROL Rd Rotate Left Through Carry Rd(0)←C,Rd(n+1)← Rd(n),C←Rd(7) Z,C,N,V 1
ROR Rd Rotate Right Through Carry Rd(7)←C,Rd(n)← Rd(n+1),C←Rd(0) Z,C,N,V 1
ASR Rd Arithmetic Shift Right Rd(n) ← Rd(n+1), n=0..6 Z,C,N,V 1
SWAP Rd Swap Nibbles Rd(3..0)←Rd(7..4),Rd(7..4)←Rd(3..0) None 1
BSET s Flag Set SREG(s) ← 1 SREG(s) 1
BCLR s Flag Clear SREG(s) ← 0 SREG(s) 1
BST Rr, b Bit Store from Register to T T ← Rr(b) T 1
BLD Rd, b Bit load from T to Register Rd(b) ← TNone1
SEC Set Carry C ← 1C1
CLC Clear Carry C ← 0 C 1
SEN Set Negative Flag N ← 1N1
CLN Clear Negative Flag N ← 0 N 1
SEZ Set Zero Flag Z ← 1Z1
CLZ Clear Zero Flag Z ← 0 Z 1
SEI Global Interrupt Enable I ← 1I1
CLI Global Interrupt Disable I ← 0 I 1
SES Set Signed Test Flag S ← 1S1
CLS Clear Signed Test Flag S ← 0 S 1
SEV Set Twos Complement Overflow. V ← 1V1
CLV Clear Twos Complement Overflow V ← 0 V 1
SET Set T in SREG T ← 1T1
CLT Clear T in SREG T ← 0 T 1
SEH Set Half Carry Flag in SREG H ← 1H1
Mnemonics Operands Description Operation Flags #Clocks
309
2513K–AVR–07/09
ATmega162/V
CLH Clear Half Carry Flag in SREG H ← 0 H 1
MCU CONTROL INSTRUCTIONS
NOP No Operation None 1
SLEEP Sleep (see specific descr. for Sleep function) None 1
WDR Watchdog Reset (see specific descr. for WDR/Timer) None 1
BREAK Break For On-chip Debug Only None N/A
Mnemonics Operands Description Operation Flags #Clocks
310
2513K–AVR–07/09
ATmega162/V
Ordering Information
Notes: 1. This device can also be supplied in wafer form. Please contact your local Atmel sales office for detailed ordering information
and minimum quantities.
2. Pb-free packaging alternative, complies to the European Directive for Restriction of Hazardous Substances (RoHS direc-
tive).Also Halide free and fully Green.
3. See Figure 113 on page 266.
4. See Figure 114 on page 266.
Speed (MHz) Power Supply Ordering Code Package(1) Operation Range
8(3) 1.8 - 5.5V
ATmega162V-8AI
ATmega162V-8PI
ATmega162V-8MI
ATmega162V-8AU(2)
ATmega162V-8PU(2)
ATmega162V-8MU(2)
44A
40P6
44M1
44A
40P6
44M1
Industrial
(-40°C to 85°C)
16(4) 2.7 - 5.5V
ATmega162-16AI
ATmega162-16PI
ATmega162-16MI
ATmega162-16AU(2)
ATmega162-16PU(2)
ATmega162-16MU(2)
44A
40P6
44M1
44A
40P6
44M1
Industrial
(-40°C to 85°C)
Package Type
44A 44-lead, Thin (1.0 mm) Plastic Gull Wing Quad Flat Package (TQFP)
40P6 40-pin, 0.600” Wide, Plastic Dual Inline Package (PDIP)
44M1 44-pad, 7 x 7 x 1.0 mm body, lead pitch 0.50 mm, Micro Lead Frame Package (QFN/MLF)
311
2513K–AVR–07/09
ATmega162/V
Packaging Information
44A
2325 Orchard Parkway
San Jose, CA 95131
TITLE DRAWING NO.
R
REV.
44A, 44-lead, 10 x 10 mm Body Size, 1.0 mm Body Thickness,
0.8 mm Lead Pitch, Thin Profile Plastic Quad Flat Package (TQFP) B
44A
10/5/2001
PIN 1 IDENTIFIER
0˚~7˚
PIN 1
L
C
A1 A2 A
D1
D
eE1 E
B
COMMON DIMENSIONS
(Unit of Measure = mm)
SYMBOL MIN NOM MAX NOTE
Notes: 1. This package conforms to JEDEC reference MS-026, Variation ACB.
2. Dimensions D1 and E1 do not include mold protrusion. Allowable
protrusion is 0.25 mm per side. Dimensions D1 and E1 are maximum
plastic body size dimensions including mold mismatch.
3. Lead coplanarity is 0.10 mm maximum.
A – – 1.20
A1 0.05 – 0.15
A2 0.95 1.00 1.05
D 11.75 12.00 12.25
D1 9.90 10.00 10.10 Note 2
E 11.75 12.00 12.25
E1 9.90 10.00 10.10 Note 2
B 0.30 – 0.45
C 0.09 – 0.20
L 0.45 – 0.75
e 0.80 TYP
312
2513K–AVR–07/09
ATmega162/V
40P6
2325 Orchard Parkway
San Jose, CA 95131
TITLE DRAWING NO.
R
REV.
40P6, 40-lead (0.600"/15.24 mm Wide) Plastic Dual
Inline Package (PDIP) B
40P6
09/28/01
PIN
1
E1
A1
B
REF
E
B1
C
L
SEATING PLANE
A
0º ~ 15º
D
e
eB
COMMON DIMENSIONS
(Unit of Measure = mm)
SYMBOL MIN NOM MAX NOTE
A – – 4.826
A1 0.381 – –
D 52.070 – 52.578 Note 2
E 15.240 – 15.875
E1 13.462 – 13.970 Note 2
B 0.356 – 0.559
B1 1.041 – 1.651
L 3.048 – 3.556
C 0.203 – 0.381
eB 15.494 – 17.526
e 2.540 TYP
Notes: 1. This package conforms to JEDEC reference MS-011, Variation AC.
2. Dimensions D and E1 do not include mold Flash or Protrusion.
Mold Flash or Protrusion shall not exceed 0.25 mm (0.010").
313
2513K–AVR–07/09
ATmega162/V
44M1
TITLE DRAWING NO.GPC REV.
Package Drawing Contact:
packagedrawings@atmel.com 44M1ZWSH
44M1, 44-pad, 7 x 7 x 1.0 mm Body, Lead
Pitch 0.50 mm, 5.20 mm Exposed Pad, Thermally
Enhanced Plastic Very Thin Quad Flat No
Lead Package (VQFN)
9/26/08
COMMON DIMENSIONS
(Unit of Measure = mm)
SYMBOL MIN NOM MAX NOTE
A 0.80 0.90 1.00
A1 – 0.02 0.05
A3 0.20 REF
b 0.180.230.30
D
D2 5.00 5.20 5.40
6.90 7.00 7.10
6.90 7.00 7.10
E
E2 5.00 5.20 5.40
e 0.50 BSC
L 0.59 0.64 0.69
K 0.20 0.26 0.41
Note: JEDEC Standard MO-220, Fig. 1 (SAW Singulation) VKKD-3.
TOP VIEW
SIDE VIEW
BOTTOM VIEW
D
E
Marked Pin# 1 ID
E2
D2
be
Pin #1 Corner
L
A1
A3
A
SEATING PLANE
Pin #1
Tr i angle
Pin #1
Chamfer
(C 0.30)
Option A
Option B
Pin #1
Notch
(0.20 R)
Option C
K
K
1
2
3
314
2513K–AVR–07/09
ATmega162/V
Errata The revision letter in this section refers to the revision of the ATmega162 device.
ATmega162, all
rev.
There are no errata for this revision of ATmega162. However, a proposal for solving problems
regarding the JTAG instruction IDCODE is presented below.
•IDCODE masks data from TDI input
•Reading EEPROM by using ST or STS to set EERE bit triggers unexpected interrupt request
•Interrupts may be lost when writing the timer register in asynchronous timer
1. IDCODE masks data from TDI input
The public but optional JTAG instruction IDCODE is not implemented correctly according to
IEEE1149.1; a logic one is scanned into the shift register instead of the TDI input while shift-
ing the Device ID Register. Hence, captured data from the preceding devices in the
boundary scan chain are lost and replaced by all-ones, and data to succeeding devices are
replaced by all-ones during Update-DR.
If ATmega162 is the only device in the scan chain, the problem is not visible.
Problem Fix / Workaround
Select the Device ID Register of the ATmega162 (Either by issuing the IDCODE instruction
or by entering the Test-Logic-Reset state of the TAP controller) to read out the contents of
its Device ID Register and possibly data from succeeding devices of the scan chain. Note
that data to succeeding devices cannot be entered during this scan, but data to preceding
devices can. Issue the BYPASS instruction to the ATmega162 to select its Bypass Register
while reading the Device ID Registers of preceding devices of the boundary scan chain.
Never read data from succeeding devices in the boundary scan chain or upload data to the
succeeding devices while the Device ID Register is selected for the ATmega162. Note that
the IDCODE instruction is the default instruction selected by the Test-Logic-Reset state of
the TAP-controller.
Alternative Problem Fix / Workaround
If the Device IDs of all devices in the boundary scan chain must be captured simultaneously
(for instance if blind interrogation is used), the boundary scan chain can be connected in
such way that the ATmega162 is the first device in the chain. Update-DR will still not work
for the succeeding devices in the boundary scan chain as long as IDCODE is present in the
JTAG Instruction Register, but the Device ID registered cannot be uploaded in any case.
2. Reading EEPROM by using ST or STS to set EERE bit triggers unexpected interrupt
request.
Reading EEPROM by using the ST or STS command to set the EERE bit in the EECR reg-
ister triggers an unexpected EEPROM interrupt request.
Problem Fix / Workaround
Always use OUT or SBI to set EERE in EECR.
3. Interrupts may be lost when writing the timer register in asynchronous timer
The interrupt will be lost if a timer register that is synchronous timer clock is written when the
asynchronous Timer/Counter register (TCNTx) is 0x00.
Problem Fix / Workaround
Always check that the asynchronous Timer/Counter register neither have the value 0xFF nor
0x00 before writing to the asynchronous Timer Control Register (TCCRx), asynchronous
Timer Counter Register (TCNTx), or asynchronous Output Compare Register (OCRx).
315
2513K–AVR–07/09
ATmega162/V
Datasheet
Revision
History
Please note that the referring page numbers in this section are referred to this document. The
referring revision in this section are referring to the document revision.
Changes from Rev.
2513J-08/07 to
Rev. 2513K-07/09
1. Updated “Errata” on page 314.
2. Updated the last page with Atmel’s new adresses.
Changes from Rev.
2513I-04/07 to Rev.
2513J-08/07
1. Updated “Features” on page 1.
2. Added “Data Retention” on page 7.
3. Updated “Errata” on page 314.
4. Updated “Version” on page 205.
5. Updated “C Code Example(1)” on page 172.
6. Updated Figure 18 on page 35.
7. Updated “Clock Distribution” on page 35.
8. Updated “SPI Serial Programming Algorithm” on page 246.
9. Updated “Slave Mode” on page 162.
Changes from Rev.
2513H-04/06 to
Rev. 2513I-04/07
1. Updated “Using all 64KB Locations of External Memory” on page 34.
2. Updated “Bit 6 – ACBG: Analog Comparator Bandgap Select” on page 195.
3. Updated VOH conditions in“DC Characteristics” on page 264.
Changes from Rev.
2513G-03/05 to
Rev. 2513H-04/06
1. Added “Resources” on page 7.
2. Updated “Calibrated Internal RC Oscillator” on page 38.
3. Updated note for Table 19 on page 50.
4. Updated “Serial Peripheral Interface – SPI” on page 157.
Changes from Rev.
2513F-09/03 to
Rev. 2513G-03/05
1. MLF-package alternative changed to “Quad Flat No-Lead/Micro Lead Frame Package
QFN/MLF”.
2. Updated “Electrical Characteristics” on page 264
3. Updated “Ordering Information” on page 310
Changes from Rev.
2513D-04/03 to
Rev. 2513E-09/03
1. Removed “Preliminary” from the datasheet.
2. Added note on Figure 1 on page 2.
316
2513K–AVR–07/09
ATmega162/V
3. Renamed and updated “On-chip Debug System” to “JTAG Interface and On-chip
Debug System” on page 46.
4. Updated Table 18 on page 48 and Table 19 on page 50.
5. Updated “Test Access Port – TAP” on page 197 regarding JTAGEN.
6. Updated description for the JTD bit on page 207.
7. Added note on JTAGEN in Table 99 on page 233.
8. Updated Absolute Maximum Ratings* and DC Characteristics in “Electrical Character-
istics” on page 264.
9. Added a proposal for solving problems regarding the JTAG instruction IDCODE in
“Errata” on page 314.
Changes from Rev.
2513C-09/02 to
Rev. 2513D-04/03
1. Updated the “Ordering Information” on page 310 and “Packaging Information” on
page 311.
2. Updated “Features” on page 1.
3. Added characterization plots under “ATmega162 Typical Characteristics” on page
275.
4. Added Chip Erase as a first step under “Programming the Flash” on page 260 and
“Programming the EEPROM” on page 262.
5. Changed CAL7, the highest bit in the OSCCAL Register, to a reserved bit on page 39
and in “Register Summary” on page 304.
6. Changed CPCE to CLKPCE on page 41.
7. Corrected code examples on page 55.
8. Corrected OCn waveforms in Figure 52 on page 120.
9. Various minor Timer1 corrections.
10. Added note under “Filling the Temporary Buffer (Page Loading)” on page 224 about
writing to the EEPROM during an SPM Page Load.
11. Added section “EEPROM Write During Power-down Sleep Mode” on page 24.
12. Added information about PWM symmetry for Timer0 on page 98 and Timer2 on page
147.
13. Updated Table 18 on page 48, Table 20 on page 50, Table 36 on page 77, Table 83 on
page 205, Table 109 on page 247, Table 112 on page 267, and Table 113 on page 268.
14. Added Figures for “Absolute Maximum Frequency as a function of VCC, ATmega162”
on page 266.
317
2513K–AVR–07/09
ATmega162/V
15. Updated Figure 29 on page 64, Figure 32 on page 68, and Figure 88 on page 210.
16. Removed Table 114, “External RC Oscillator, Typical Frequencies(1),” on page 265.
17. Updated “Electrical Characteristics” on page 264.
Changes from Rev.
2513B-09/02 to
Rev. 2513C-09/02
1. Changed the Endurance on the Flash to 10,000 Write/Erase Cycles.
Changes from Rev.
2513A-05/02 to
Rev. 2513B-09/02
1. Added information for ATmega162U.
Information about ATmega162U included in “Features” on page 1, Table 19, “BODLEVEL
Fuse Coding,” on page 50, and “Ordering Information” on page 310.
318
2513K–AVR–07/09
ATmega162/V
i
2513K–AVR–07/09
ATmega162/V
Table of Contents
Features 1
Pin Configurations 2
Disclaimer 2
Overview 3
Block Diagram 3
ATmega161 and ATmega162 Compatibility 4
Pin Descriptions 5
Resources 7
Data Retention 7
About Code Examples 8
AVR CPU Core 9
Introduction 9
Architectural Overview 9
ALU – Arithmetic Logic Unit 10
Status Register 10
General Purpose Register File 12
Stack Pointer 13
Instruction Execution Timing 14
Reset and Interrupt Handling 14
AVR ATmega162 Memories 17
In-System Reprogrammable Flash Program Memory 17
SRAM Data Memory 18
EEPROM Data Memory 19
I/O Memory 25
External Memory Interface 26
XMEM Register Description 30
ii
2513K–AVR–07/09
ATmega162/V
System Clock and Clock Options 35
Clock Systems and their Distribution 35
Clock Sources 36
Default Clock Source 36
Crystal Oscillator 36
Low-frequency Crystal Oscillator 38
Calibrated Internal RC Oscillator 38
External Clock 40
Clock output buffer 40
Timer/Counter Oscillator 41
System Clock Prescaler 41
Power Management and Sleep Modes 43
Idle Mode 44
Power-down Mode 44
Power-save Mode 45
Standby Mode 45
Extended Standby Mode 45
Minimizing Power Consumption 46
System Control and Reset 47
Internal Voltage Reference 52
Watchdog Timer 52
Timed Sequences for Changing the Configuration of the Watchdog Timer 56
Interrupts 57
Interrupt Vectors in ATmega162 57
I/O-Ports 63
Introduction 63
Ports as General Digital I/O 63
Alternate Port Functions 68
Register Description for I/O-Ports 82
External Interrupts 84
8-bit Timer/Counter0 with PWM 89
Overview 89
Timer/Counter Clock Sources 90
Counter Unit 91
Output Compare Unit 91
Compare Match Output Unit 93
Modes of Operation 94
Timer/Counter Timing Diagrams 98
8-bit Timer/Counter Register Description 100
iii
2513K–AVR–07/09
ATmega162/V
Timer/Counter0, Timer/Counter1, and Timer/Counter3 Prescalers 104
16-bit Timer/Counter (Timer/Counter1 and Timer/Counter3) 106
Restriction in ATmega161 Compatibility Mode 106
Overview 106
Accessing 16-bit Registers 109
Timer/Counter Clock Sources 112
Counter Unit 112
Input Capture Unit 113
Output Compare Units 114
Compare Match Output Unit 117
Modes of Operation 118
Timer/Counter Timing Diagrams 126
16-bit Timer/Counter Register Description 128
8-bit Timer/Counter2 with PWM and Asynchronous operation 138
Overview 138
Timer/Counter Clock Sources 139
Counter Unit 140
Output Compare Unit 140
Compare Match Output Unit 142
Modes of Operation 143
Timer/Counter Timing Diagrams 147
8-bit Timer/Counter Register Description 149
Asynchronous operation of the Timer/Counter 152
Timer/Counter Prescaler 156
Serial Peripheral Interface – SPI 157
SS Pin Functionality 162
Data Modes 165
USART 166
Dual USART 166
Clock Generation 168
Frame Formats 171
USART Initialization 172
Data Transmission – The USART Transmitter 173
Data Reception – The USART Receiver 175
Asynchronous Data Reception 179
Multi-processor Communication Mode 182
Accessing UBRRH/
UCSRC Registers 184
USART Register Description 186
Examples of Baud Rate Setting 191
iv
2513K–AVR–07/09
ATmega162/V
Analog Comparator 195
JTAG Interface and On-chip Debug System 197
Features 197
Overview 197
Test Access Port – TAP 197
TAP Controller 200
Using the Boundary-scan Chain 200
Using the On-chip Debug system 201
On-chip debug specific JTAG instructions 202
On-chip Debug Related Register in I/O Memory 202
Using the JTAG Programming Capabilities 202
Bibliography 203
IEEE 1149.1 (JTAG) Boundary-scan 204
Features 204
System Overview 204
Data Registers 205
Boundary-scan Specific JTAG Instructions 206
Boundary-scan Chain 208
ATmega162 Boundary-scan Order 213
Boundary-scan Description Language Files 216
Boot Loader Support – Read-While-Write Self-programming 217
Features 217
Application and Boot Loader Flash Sections 217
Read-While-Write and No Read-While-Write Flash Sections 217
Boot Loader Lock Bits 219
Entering the Boot Loader Program 221
Addressing the Flash During Self-programming 223
Self-programming the Flash 224
Memory Programming 231
Program And Data Memory Lock Bits 231
Fuse Bits 232
Signature Bytes 234
Calibration Byte 234
Parallel Programming Parameters, Pin Mapping, and Commands 234
Parallel Programming 236
Serial Downloading 245
SPI Serial Programming Pin Mapping 245
Programming via the JTAG Interface 250
v
2513K–AVR–07/09
ATmega162/V
Electrical Characteristics 264
Absolute Maximum Ratings* 264
DC Characteristics 264
External Clock Drive Waveforms 267
External Clock Drive 267
SPI Timing Characteristics 268
External Data Memory Timing 270
ATmega162 Typical Characteristics 275
Register Summary 304
Instruction Set Summary 307
Ordering Information 310
Packaging Information 311
44A 311
40P6 312
44M1 313
Errata 314
ATmega162, all rev. 314
Datasheet Revision History 315
Changes from Rev. 2513I-04/07 to Rev. 2513J-08/07 315
Changes from Rev. 2513H-04/06 to Rev. 2513I-04/07 315
Changes from Rev. 2513G-03/05 to Rev. 2513H-04/06 315
Changes from Rev. 2513F-09/03 to Rev. 2513G-03/05 315
Changes from Rev. 2513D-04/03 to Rev. 2513E-09/03 315
Changes from Rev. 2513C-09/02 to Rev. 2513D-04/03 316
Changes from Rev. 2513B-09/02 to Rev. 2513C-09/02 317
Changes from Rev. 2513A-05/02 to Rev. 2513B-09/02 317
2513K–AVR–07/09
Headquarters International
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