Atmel ATmega32M1, ATmega64C1, ATmega16M1, ATmega32C1, ATmega64M1 User Manual

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 1MIPS throughput per MHz – On-chip 2-cycle Multiplier

• Data and Non-Volatile Program Memory

– 16K/32K/64K Bytes Flash of In-System Programmable Program Memory

• Endurance: 10,000 Write/Erase Cycles – Optional Boot Code Section with Independent Lock Bits – In-System Programming by On-chip Boot Program

• True Read-While-Write Operation – 512/1024/2048 Bytes of In-System Programmable EEPROM

• Endurance: 100,000 Write/Erase Cycles

• Programming Lock for Flash Program and EEPROM Data Security

• 1024/2048/4096 Bytes Internal SRAM

• On Chip Debug Interface (debugWIRE)

• CAN 2.0A/B with 6 Message Objects - ISO 16845 Certified

• LIN 2.1 and 1.3 Controller or 8-Bit UART

• One 12-bit High Speed PSC (Power Stage Controller) (only ATmega16/32/64M1)

• Non Overlapping Inverted PWM Output Pins With Flexible Dead-Time

• Variable PWM duty Cycle and Frequency

• Synchronous Update of all PWM Registers

• Auto Stop Function for Emergency Event

• Peripheral Features

– One 8-bit General purpose Timer/Counter with Separate Prescaler, Compare Mode

and Capture Mode

– One 16-bit General purpose Timer/Counter with Separate Prescaler, Compare

Mode and Capture Mode – One Master/Slave SPI Serial Interface – 10-bit ADC

• Up To 11 Single Ended Channels and 3 Fully Differential ADC Channel Pairs

• Programmable Gain (5x, 10x, 20x, 40x) on Differential Channels

• Internal Reference Voltage

• Direct Power Supply Voltage Measurement – 10-bit DAC for Variable Voltage Reference (Comparators, ADC) – Four Analog Comparators with Variable Threshold Detection – 100µA ±6% Current Source (LIN Node Identification) – Interrupt and Wake-up on Pin Change – Programmable Watchdog Timer with Separate On-Chip Oscillator – On-chipTemperature Sensor

• Special Microcontroller Features

– Low Power Idle, Noise Reduction, and Power Down Modes – Power On Reset and Programmable Brown Out Detection – In-System Programmable via SPI Port – High Precision Crystal Oscillator for CAN Operations (16MHz)

1. See certification on Atmel

web site and note on “Baud Rate” on page 177.

(1)

8-bit Microcontroller with 16K/32K/64K Bytes In-System Programmable Flash

Atmel ATmega16M1 ATmega32M1 ATmega64M1 ATmega32C1 ATmega64C1

Automotive

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– Internal Calibrated RC Oscillator (8MHz) – On-chip PLL for fast PWM (32MHz, 64MHz) and CPU (16MHz)

• Operating Voltage:

– 2.7V - 5.5V

• Extended Operating Temperature:

– –40°C to +125°C

• Core Speed Grade:

– 0 - 8MHz at 2.7 - 4.5V – 0 - 16MHz at 4.5 - 5.5V

ATmega32/64/M1/C1 Product Line-up

Part Number ATmega32C1 ATmega64C1 ATmega16M1 ATmega32M1 ATmega64M1

Flash Size 32 Kbyte 64 Kbyte 16 Kbyte 32 Kbyte 64 Kbyte

RAM Size 2048 bytes 4096 bytes 1024 bytes 2048 bytes 4096 bytes

EEPROM Size 1024 bytes 2048 bytes 512 bytes 1024 bytes 2048 bytes

8-bit Timer Yes

16-bit Timer Yes

PSC No Yes

PWM Outputs 4 4 10 10 10

Fault Inputs (PSC) 0 0 3 3 3

PLL 32/64MHz

10-bit ADC Channels

10-bit DAC Yes

Analog Comparators 4

Current Source Yes

CAN Ye s

LIN/UART Yes

On-Chip Temp. Sensor Yes

SPI Interface Yes

11 single

3 Differential

Atmel ATmega16/32/64/M1/C1

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1. Pin Configurations

1 2 3 4 5 6 7 8

24 23 22 21 20 19 18 17

(PCINT18/PSCIN2/OC1A/MISO_A) PD2

(PCINT19/TXD/TXLIN/OC0A/SS/MOSI_A) PD3

(PCINT9/PSCIN1/OC1B/SS_A) PC1

VCC

GND

(PCINT10/T0/TXCAN) PC2

(PCINT11/T1/RXCAN/ICP1B) PC3

(PCINT0/MISO/PSCOUT2A) PB0

PB4 (AMP0+/PCINT4) PB3 (AMP0-/PCINT3) PC6 (ADC10/ACMP1/PCINT14) AREF(ISRC) AGND AVCC PC5 (ADC9/ACMP3/AMP1+/PCINT13) PC4 (ADC8/ACMPN3/AMP1-/PCINT12)

32313029282726

9101112131415

(PCINT1/MOSI/PSCOUT2B) PB1

(PCINT25/OC0B/XTAL1) PE1

(PCINT26/ADC0/XTAL2) PE2

(ADC2/ACMP2/PCINT21) PD5

(ADC3/ACMPN2/INT0/PCINT22) PD6

(ACMP0/PCINT23) PD7

(ADC5/INT1/ACMPN0/PCINT2) PB2

PD1

(PCINT17/PSCIN0/CLKO)

PE0

(PCINT24/RESET/OCD)

PC0

(PCINT8/INT3/PSCOUT1A)

PD0

(PCINT16/PSCOUT0A)

PB7 (ADC4/PSCOUT0B/SCK/PCINT7)

PB6 (ADC7/PSCOUT1B/PCINT6)

PB5 (ADC6/INT2/ACMPN1/AMP2-/PCINT5)

PC7 (D2A/AMP2+/PCINT15)

ATmega32/64M1 TQFP32/QFN32

Figure 1-1. ATmega16/32/64M1 TQFP32/QFN32 (7*7 mm) Package.

Atmel ATmega16/32/64/M1/C1

Note: On the engineering samples (Parts marked AT90PWM324), the ACMPN3 alternate function is not

located on PC4. It is located on PE2.

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Figure 1-2. ATmega32/64C1 TQFP32/QFN32 (7*7 mm) Package

ATmega32/64C1 TQFP32/QFN32

(PCINT16)

(PCINT24/RESET/OCD)

(PCINT17/CLKO)

(PCINT8/INT3)

PD1

PE0

PC0

PD0

PB7 (ADC4/SCK/PCINT7)

PB6 (ADC7PCINT6)

PB5 (ADC6/INT2/ACMPN1/AMP2-/PCINT5)

PC7 (D2A/AMP2+/PCINT15)

(PCINT18/OC1A/MISO_A) PD2

(PCINT19/TXD/TXLIN/OC0A/SS/MOSI_A) PD3

(PCINT9/OC1B/SS_A) PC1

VCC

GND

(PCINT10/T0/TXCAN) PC2

(PCINT11/T1/RXCAN/ICP1B) PC3

(PCINT0/MISO) PB0

32313029282726

1 2 3 4 5 6 7 8

9101112131415

(PCINT1/MOSI) PB1

(PCINT25/OC0B/XTAL1) PE1

PB4 (AMP0+/PCINT4)

PB3 (AMP0-/PCINT3)

PC6 (ADC10/ACMP1/PCINT14) AREF(ISRC)

AGND

AVCC

PC5 (ADC9/ACMP3/AMP1+/PCINT13)

PC4 (ADC8/ACMPN3/AMP1-/PCINT12)

(ACMP0/PCINT23) PD7

(PCINT26/ADC0/XTAL2) PE2

(ADC2/ACMP2/PCINT21) PD5

(ADC5/INT1/ACMPN0/PCINT2) PB2

(ADC3/ACMPN2/INT0/PCINT22) PD6

(PCINT20/ADC1/RXD/RXLIN/ICP1A/SCK_A) PD4

Note: On the first engineering samples (Parts marked AT90PWM324), the ACMPN3 alternate function is

not located on PC4. It is located on PE2.

Atmel ATmega16/32/64/M1/C1

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1.1 Pin Descriptions

Table 1-1. Pin out description

QFN32 Pin

Atmel ATmega16/32/64/M1/C1

Number Mnemonic Type Name, Function and Alternate Function

5GNDPowerGround: 0V reference

20 AGND Power Analog Ground: 0V reference for analog part

4 VCC Power Power Supply

Analog Power Supply: This is the power supply voltage for

19 AVCC Power

21 AREF Power

8 PB0 I/O

analog part For a normal use this pin must be connected.

Analog Reference : reference for analog converter . This is the reference voltage of the A/D converter. As output, can be used by external analog

ISRC (Current Source Output)

MISO (SPI Master In Slave Out) PSCOUT2A (PSC Module 2 Output A) PCINT0 (Pin Change Interrupt 0)

9 PB1 I/O

16 PB2 I/O

23 PB3 I/O

24 PB4 I/O

26 PB5 I/O

27 PB6 I/O

28 PB7 I/O

MOSI (SPI Master Out Slave In) PSCOUT2B (PSC Module 2 Output B) PCINT1 (Pin Change Interrupt 1)

ADC5 (Analog Input Channel 5 ) INT1 (External Interrupt 1 Input) ACMPN0 (Analog Comparator 0 Negative Input) PCINT2 (Pin Change Interrupt 2)

AMP0- (Analog Differential Amplifier 0 Negative Input) PCINT3 (Pin Change Interrupt 3)

AMP0+ (Analog Differential Amplifier 0 Positive Input) PCINT4 (Pin Change Interrupt 4)

ADC6 (Analog Input Channel 6) INT2 (External Interrupt 2 Input) ACMPN1 (Analog Comparator 1 Negative Input) AMP2- (Analog Differential Amplifier 2 Negative Input) PCINT5 (Pin Change Interrupt 5)

ADC7 (Analog Input Channel 7) PSCOUT1B (PSC Module 1 Output A) PCINT6 (Pin Change Interrupt 6)

ADC4 (Analog Input Channel 4) PSCOUT0B (PSC Module 0 Output B) SCK (SPI Clock) PCINT7 (Pin Change Interrupt 7)

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Note: 1. On the first engineering samples (Parts marked AT90PWM324), the ACMPN3 alternate

function is not located on PC4. It is located on PE2.

Table 1-1. Pin out description (Continued)

QFN32 Pin

Number Mnemonic Type Name, Function and Alternate Function

PSCOUT1A (PSC Module 1 Output A)

30 PC0 I/O

3 PC1 I/O

6 PC2 I/O

7 PC3 I/O

17 PC4 I/O

INT3 (External Interrupt 3 Input) PCINT8 (Pin Change Interrupt 8)

PSCIN1 (PSC Digital Input 1) OC1B (Timer 1 Output Compare B) SS_A (Alternate SPI Slave Select) PCINT9 (Pin Change Interrupt 9)

T0 (Timer 0 clock input) TXCAN (CAN Transmit Output) PCINT10 (Pin Change Interrupt 10)

T1 (Timer 1 clock input) RXCAN (CAN Receive Input) ICP1B (Timer 1 input capture alternate B input) PCINT11 (Pin Change Interrupt 11)

ADC8 (Analog Input Channel 8) AMP1- (Analog Differential Amplifier 1 Negative Input) ACMPN3 (Analog Comparator 3 Negative Input) PCINT12 (Pin Change Interrupt 12)

ADC9 (Analog Input Channel 9)

18 PC5 I/O

22 PC6 I/O

25 PC7 I/O

29 PD0 I/O

32 PD1 I/O

1 PD2 I/O

Note: 1. On the first engineering samples (Parts marked AT90PWM324), the ACMPN3 alternate

function is not located on PC4. It is located on PE2.

AMP1+ (Analog Differential Amplifier 1 Positive Input) ACMP3 (Analog Comparator 3 Positive Input) PCINT13 (Pin Change Interrupt 13)

ADC10 (Analog Input Channel 10) ACMP1 (Analog Comparator 1 Positive Input) PCINT14 (Pin Change Interrupt 14)

D2A (DAC output) AMP2+ (Analog Differential Amplifier 2 Positive Input) PCINT15 (Pin Change Interrupt 15)

PSCOUT0A (PSC Module 0 Output A) PCINT16 (Pin Change Interrupt 16)

PSCIN0 (PSC Digital Input 0) CLKO (System Clock Output) PCINT17 (Pin Change Interrupt 17)

OC1A (Timer 1 Output Compare A) PSCIN2 (PSC Digital Input 2) MISO_A (Programming & alternate SPI Master In Slave Out) PCINT18 (Pin Change Interrupt 18)

Atmel ATmega16/32/64/M1/C1

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Atmel ATmega16/32/64/M1/C1

Table 1-1. Pin out description (Continued)

QFN32 Pin

Number Mnemonic Type Name, Function and Alternate Function

TXD (UART Tx data) TXLIN (LIN Transmit Output)

2 PD3 I/O

12 PD4 I/O

13 PD5 I/O

OC0A (Timer 0 Output Compare A) SS (SPI Slave Select) MOSI_A (Programming & alternate Master Out SPI Slave In) PCINT19 (Pin Change Interrupt 19)

ADC1 (Analog Input Channel 1) RXD (UART Rx data) RXLIN (LIN Receive Input) ICP1A (Timer 1 input capture alternate A input) SCK_A (Programming & alternate SPI Clock) PCINT20 (Pin Change Interrupt 20)

ADC2 (Analog Input Channel 2) ACMP2 (Analog Comparator 2 Positive Input) PCINT21 (Pin Change Interrupt 21)

ADC3 (Analog Input Channel 3)

14 PD6 I/O

15 PD7 I/O

31 PE0 I/O or I

10 PE1 I/O

11 PE2 I/O

Note: 1. On the first engineering samples (Parts marked AT90PWM324), the ACMPN3 alternate

function is not located on PC4. It is located on PE2.

ACMPN2 (Analog Comparator 2 Negative Input) INT0 (External Interrupt 0 Input) PCINT22 (Pin Change Interrupt 22)

ACMP0 (Analog Comparator 0 Positive Input) PCINT23 (Pin Change Interrupt 23)

RESET (Reset Input) OCD (On Chip Debug I/O) PCINT24 (Pin Change Interrupt 24)

XTAL1 (XTAL Input) OC0B (Timer 0 Output Compare B) PCINT25 (Pin Change Interrupt 25)

XTAL2 (XTAL Output) ADC0 (Analog Input Channel 0) PCINT26 (Pin Change Interrupt 26)

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2. Overview

Flash Program

Memory

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

4 Analog

Comparators

DAC

ADC

MPSC

Timer 1

Timer 0

HW LIN/UART

CAN

Current Source

2.1 Block Diagram

The ATmega16/32/64/M1/C1 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 ATmega16/32/64/M1/C1 achieves throughputs approaching 1 MIPS per MHz allowing the system designer to optimize power consumption versus processing speed.

Figure 2-1. Block Diagram

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 conventional CISC microcontrollers.

Atmel ATmega16/32/64/M1/C1

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Atmel ATmega16/32/64/M1/C1

The ATmega16/32/64/M1/C1 provides the following features: 16K/32K/64K bytes of In-System Programmable Flash with Read-While-Write capabilities, 512/1024/2048 bytes EEPROM, 1024/2048/4096 bytes SRAM, 27 general purpose I/O lines, 32 general purpose working registers, one Motor Power Stage Controller, two flexible Timer/Counters with compare modes and PWM, one UART with HW LIN, an 11-channel 10-bit ADC with two differential input stages with programmable gain, a 10-bit DAC, a programmable Watchdog Timer with Internal Individual Oscillator, an SPI serial port, an On-chip Debug system and four software selectable power saving modes.

The Idle mode stops the CPU while allowing the SRAM, Timer/Counters, SPI ports, CAN, LIN/UART 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. The ADC Noise Reduction mode stops the CPU and all I/O modules except ADC, to minimize switching noise during ADC conversions. 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.

The device is manufactured using Atmel’s high-density nonvolatile memory technology. The On-chip ISP Flash allows the program memory to be reprogrammed in-system through an SPI serial interface, by a conventional nonvolatile memory programmer, or by an On-chip Boot program 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 ATmega16/32/64/M1/C1 is a powerful microcontroller that provides a highly flexible and cost effective solution to many embedded control applications.

The ATmega16/32/64/M1/C1 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.

2.2 Automotive Quality Grade

The ATmega16/32/64/M1/C1 have been developed and manufactured according to the most stringent requirements of the international standard ISO-TS-16949. This data sheet contains limit values extracted from the results of extensive characterization (Temperature and Voltage). The quality and reliability of the ATmega16/32/64/M1/C1 have been verified during regular product qualification as per AEC-Q100 grade 1.

As indicated in the ordering information paragraph, the products are available in only one temperature grade.

Table 2-1. Temperature Grade Identification for Automotive Products

Temperature Temperature Identifier Comments

-40 ; +125 Z Full AutomotiveTemperature Range

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2.3 Pin Descriptions

2.3.1 VCC

Digital supply voltage.

2.3.2 GND

Ground.

2.3.3 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 ATmega16/32/64/M1/C1 as listed on page 69.

2.3.4 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.

Port C also serves the functions of special features of the ATmega16/32/64/M1/C1 as listed on

page 72.

2.3.5 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 ATmega16/32/64/M1/C1 as listed on page 75.

2.3.6 Port E (PE2..0) RESET/

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.

If the RSTDISBL Fuse is programmed, PE0 is used as an I/O pin. Note that the electrical characteristics of PE0 differ from those of the other pins of Port E.

If the RSTDISBL Fuse is unprogrammed, PE0 is used as a 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 7-1 on page 47. Shorter pulses are not guaranteed to generate a Reset.

XTAL1/ XTAL2

Atmel ATmega16/32/64/M1/C1

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Depending on the clock selection fuse settings, PE1 can be used as input to the inverting Oscillator amplifier and input to the internal clock operating circuit.

Depending on the clock selection fuse settings, PE2 can be used as output from the inverting Oscillator amplifier.

The various special features of Port E are elaborated in “Alternate Functions of Port E” on page

78 and “Clock Systems and their Distribution” on page 29.

2.3.7 AVCC

AVCC is the supply voltage pin for the A/D Converter, D/A Converter, Current source. It should be externally connected to V be connected to V

Techniques” on page 238).

2.3.8 AREF

This is the analog reference pin for the A/D Converter.

2.4 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 documentation for more details.

Atmel ATmega16/32/64/M1/C1

, even if the ADC, DAC are not used. If the ADC is used, it should

through a low-pass filter (see Section 18.6.2 “Analog Noise Canceling

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3. AVR CPU Core

Flash

Program

Memory

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

3.1 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.

3.2 Architectural Overview

Figure 3-1. 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 instruction 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.

Atmel ATmega16/32/64/M1/C1

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Atmel ATmega16/32/64/M1/C1

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 typical 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 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 operation, 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 format. 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 (Store Program Memory) 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 position. The lower the Interrupt Vector address, the higher is the priority.

The I/O memory space contains 64 addresses for CPU peripheral functions as Control Registers, 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. In addition, the ATmega16/32/64/M1/C1 has Extended I/O space from 0x60 - 0xFF in SRAM where only the ST/STS/STD and LD/LDS/LDD instructions can be used.

3.3 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.

7647H–AVR–03/12

3.4 Status Register

The Status Register contains information about the result of the most recently executed arithmetic 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

• Bit 7 – I: Global Interrupt Enable

The Global Interrupt Enable bit must be set to enabled the interrupts. The individual interrupt 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 destination 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.

Atmel ATmega16/32/64/M1/C1

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• 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.

3.5 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 3-2 shows the structure of the 32 general purpose working registers in the CPU.

Figure 3-2. AVR CPU General Purpose Working Registers

General R14 0x0E Purpose R15 0x0F Working R16 0x10 Registers R17 0x11

Atmel ATmega16/32/64/M1/C1

70Addr.

R0 0x00 R1 0x01 R2 0x02 … R13 0x0D

… 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

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 3-2, 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 implemented 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.

3.5.1 The X-register, Y-register, and Z-register

The registers R26..R31 have some added functions to their general purpose usage. These registers 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 3-3.

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3.6 Stack Pointer

Figure 3-3. The X-, Y-, and Z-registers

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)

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).

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 locations 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 0x100. 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 implementations of the AVR architecture is so small that only SPL is needed. In this case, the SPH Register will not be present.

Bit 1514131211109 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 Top address of the SRAM (0x04FF/0x08FF/0x10FF)

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3.7 Instruction Execution Timing

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

ALU Operation Execute

Result Write Back

T1 T2 T3 T4

clk

CPU

This section describes the general access timing concepts for instruction execution. The AVR CPU is driven by the CPU clock clk chip. No internal clock division is used.

Figure 3-4 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 3-4. The Parallel Instruction Fetches and Instruction Executions

Atmel ATmega16/32/64/M1/C1

, directly generated from the selected clock source for the

CPU

Figure 3-5 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 destination register.

Figure 3-5. Single Cycle ALU Operation

3.8 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 296 for details.

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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 ANACOMP0 – the Analog Comparator 0 Interrupt. The Interrupt Vectors can be moved to the start of the Boot Flash section by setting the IVSEL bit in the MCU Control Register (MCUCR). 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 programming the BOOTRST Fuse, see “Boot Loader Support – Read-While-Write

Self-Programming ATmega16/32/64/M1/C1” on page 279.

3.8.1 Interrupt Behavior

When an interrupt occurs, the Global Interrupt Enable I-bit is cleared and all interrupts are disabled. 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 Vector 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.

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Atmel ATmega16/32/64/M1/C1

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) */

When using the SEI instruction to enable interrupts, the instruction following SEI will be executed before any pending interrupts, as shown in this example.

Assembly Code Example

C Code Example

3.8.2 Interrupt Response Time

The interrupt execution response for all the enabled AVR interrupts is four clock cycles minimum. 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.

sei ; set Global Interrupt Enable sleep; enter sleep, waiting for interrupt

; note: will enter sleep before any pending ; interrupt(s)

_SEI(); /* set Global Interrupt Enable */ _SLEEP(); /* enter sleep, waiting for interrupt */ /* note: will enter sleep before any pending interrupt(s) */

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4. Memories

This section describes the different memories in the ATmega16/32/64/M1/C1. The AVR architecture has two main memory spaces, the Data Memory and the Program Memory space. In addition, the ATmega16/32/64/M1/C1 features an EEPROM Memory for data storage. All three memory spaces are linear and regular.

4.1 In-System Reprogrammable Flash Program Memory

The ATmega16/32/64/M1/C1 contains 16K/32K/64K 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, 16K x 16 , 32K 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 ATmega16/32/64/M1/C1 Program Counter (PC) is 14/15 bits wide, thus addressing the 8K/16K/32K 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 ATmega16/32/64/M1/C1” on page 279. “Memory Programming” on page 296 contains a detailed description on Flash programming in SPI or Parallel

programming mode. Constant tables can be allocated within the entire program memory address space (see the LPM

– Load Program Memory. Timing diagrams for instruction fetch and execution are presented in “Instruction Execution Tim-

ing” on page 17.

Figure 4-1. Program Memory Map

Program Memory

Application Flash Section

Boot Flash Section

0x0000

0x1FFF/0x3FFF/0x7

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4.2 SRAM Data Memory

Figure 4-2 shows how the ATmega16/32/64/M1/C1 SRAM Memory is organized.

The ATmega16/32/64/M1/C1 is a complex microcontroller with more peripheral units than can be supported within the 64 locations 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 lower 2304 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 1024/2048/4096 locations address the internal data SRAM.

The five different addressing modes for the data memory cover: Direct, Indirect with Displacement, 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.

Atmel ATmega16/32/64/M1/C1

The 32 general purpose working registers, 64 I/O Registers, 160 Extended I/O Registers, and the 1024/2048/4096 bytes of internal data SRAM in the ATmega16/32/64/M1/C1 are all accessible through all these addressing modes. The Register File is described in “General Purpose

Figure 4-2. Data Memory Map for 1024/2048/4096 Internal SRAM

4.2.1 SRAM Data Access Times

This section describes the general access timing concepts for internal memory access. The internal data SRAM access is performed in two clk

page 22.

Data Memory

32 Registers 64 I/O Registers 160 Ext I/O Reg.

Internal SRAM (1024x8) (2048x8) (4096x8)

0x0000 - 0x001F 0x0020 - 0x005F 0x0060 - 0x00FF

0x0100

0x04FF/0x08FF/0x10FF

cycles as described in Figure 4-3 on

CPU

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Figure 4-3. On-chip Data SRAM Access Cycles

clk

Data

Address

Address valid

T1 T2 T3

Compute Address

Read

Write

CPU

Memory Access Instruction

Next Instruction

4.3 EEPROM Data Memory

The ATmega16/32/64/M1/C1 contains 512/1024/2048 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.

For a detailed description of SPI and Parallel data downloading to the EEPROM, see “Serial

Downloading” on page 313 , and “Parallel Programming Parameters, Pin Mapping, and Commands” on page 301 respectively.

4.3.1 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 4-2. A self-timing 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, V period of time to run at a voltage lower than specified as minimum for the clock frequency used.

See “Preventing EEPROM Corruption” on page 27.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.

is likely to rise or fall slowly on power-up/down. This causes the device for some

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Atmel ATmega16/32/64/M1/C1

4.3.2 The EEPROM Address Registers – EEARH and EEARL

Bit 15141312 11 10 9 8

– – – – – EEAR10 EEAR9 EEAR8 EEARH

EEAR7 EEAR6 EEAR5 EEAR4 EEAR3 EEAR2 EEAR1 EEAR0 EEARL

76543 2 10

Read/Write R R 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

Initial Value 0 0 0 0 0 X X X

XXXX X X XX

• Bits 15.11 – Reserved Bits

These bits are reserved bits in the ATmega16/32/64/M1/C1 and will always read as zero.

• Bits 9..0 – EEAR10..0: EEPROM Address

The EEPROM Address Registers – EEARH and EEARL specify the EEPROM address in the 512/1024/2048 bytes EEPROM space. The EEPROM data bytes are addressed linearly between 0 and 511/1023/2047. The initial value of EEAR is undefined. A proper value must be written before the EEPROM may be accessed.

4.3.3 The EEPROM Data Register – EEDR

Bit 76543210

EEDR7 EEDR6 EEDR5 EEDR4 EEDR3 EEDR2 EEDR1 EEDR0 EEDR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value00000000

• 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.

4.3.4 The EEPROM Control Register – EECR

Bit 76543210

– – EEPM1 EEPM0 EERIE EEMWE EEWE EERE EECR

Read/Write R R R/W R/W R/W R/W R/W R/W Initial Value 0 0 X X 0 0 X 0

• Bits 7..6 – Reserved Bits

These bits are reserved bits in the ATmega16/32/64/M1/C1 and will always read as zero.

• Bits 5..4 – EEPM1 and EEPM0: EEPROM Programming Mode Bits

The EEPROM Programming mode bit setting defines which programming action that will be triggered when writing EEWE. It is possible to program data in one atomic operation (erase the old value and program the new value) or to split the Erase and Write operations in two different operations. The Programming times for the different modes are shown in Table 4-1 on page 24.

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While EEWE is set, any write to EEPMn will be ignored. During reset, the EEPMn bits will be reset to 0b00 unless the EEPROM is busy programming.

Table 4-1. EEPROM Mode Bits

EEPM1 EEPM0 Programming Time Operation

0 0 3.4 ms Erase and Write in one operation (Atomic Operation)

0 1 1.8 ms Erase Only

1 0 1.8 ms Write Only

1 1 – Reserved for future use

• 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 interrupt when EEWE is cleared. The interrupt will not be generated during EEPROM write or SPM.

• 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, otherwise 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 (Store Program Memory Enable) in SPMCSR (Store Program Memory Control and Status Register) 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 ATmega16/32/64/M1/C1” on page 279 for

details about Boot programming. 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 software 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.

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Atmel ATmega16/32/64/M1/C1

• 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 4-2 lists the typical programming time for EEPROM access from the CPU.

Table 4-2. EEPROM Programming Time.

Symbol Number of Calibrated RC Oscillator Cycles Typ Programming Time

EEPROM write (from CPU)

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.

26368 3.3 ms

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Assembly Code Example

EEPROM_write:

; Wait for completion of previous write

sbic EECR,EEWE rjmp EEPROM_write

; Set up address (r18:r17) in address register

out EEARH, r18 out EEARL, r17

; Write data (r16) to data register

out EEDR,r16

; Write logical one to EEMWE

sbi EECR,EEMWE

; Start eeprom write by setting EEWE

sbi EECR,EEWE ret

C Code Example

void EEPROM_write (unsigned int uiAddress, unsigned char ucData) {

/* Wait for completion of previous write */ while(EECR & (1<<EEWE))

; /* Set up address and data registers */ EEAR = uiAddress; EEDR = ucData; /* Write logical one to EEMWE */ EECR |= (1<<EEMWE);

/* Start eeprom write by setting EEWE */

EECR |= (1<<EEWE);

}

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Atmel ATmega16/32/64/M1/C1

The next code examples show assembly and C functions for reading the EEPROM. The examples assume that interrupts are controlled so that no interrupts will occur during execution of these functions.

Assembly Code Example

EEPROM_read:

; Wait for completion of previous write

sbic EECR,EEWE rjmp EEPROM_read

; Set up address (r18:r17) in address register

out EEARH, r18 out EEARL, r17

; Start eeprom read by writing EERE

sbi EECR,EERE

; Read data from data register

in r16,EEDR ret

C Code Example

unsigned char EEPROM_read(unsigned int uiAddress) {

/* Wait for completion of previous write */

while(EECR & (1<<EEWE))

; /* Set up address register */ EEAR = uiAddress; /* Start eeprom read by writing EERE */ EECR |= (1<<EERE);

/* Return data from data register */

return EEDR;

}

4.3.5 Preventing EEPROM Corruption

During periods of low V 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. Secondly, 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:

the EEPROM data can be corrupted because the supply voltage is

CC,

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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 V

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.

4.4 I/O Memory

The I/O space definition of the ATmega16/32/64/M1/C1 is shown in “Register Summary” on

page 347.

All ATmega16/32/64/M1/C1 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 ATmega16/32/64/M1/C1 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.

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, unlike most other AVR’s, the CBI and SBI instructions will only operate on the specified bit, and can therefore be used on registers containing such status flags. The CBI and SBI instructions work with registers 0x00 to 0x1F only.

The I/O and peripherals control registers are explained in later sections.

4.5 General Purpose I/O Registers

The ATmega16/32/64/M1/C1 contains four General Purpose I/O Registers. These registers can be used for storing any information, and they are particularly useful for storing global variables and status flags.

The General Purpose I/O Registers, within the address range 0x00 - 0x1F, are directly bit-accessible using the SBI, CBI, SBIS, and SBIC instructions.

4.5.1 General Purpose I/O Register 0 – GPIOR0

Bit 76543210

GPIOR07 GPIOR06 GPIOR05 GPIOR04 GPIOR03 GPIOR02 GPIOR01 GPIOR00 GPIOR0

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value00000000

4.5.2 General Purpose I/O Register 1 – GPIOR1

Bit 76543210

GPIOR17 GPIOR16 GPIOR15 GPIOR14 GPIOR13 GPIOR12 GPIOR11 GPIOR10 GPIOR1

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value00000000

4.5.3 General Purpose I/O Register 2 – GPIOR2

Bit 76543210

GPIOR27 GPIOR26 GPIOR25 GPIOR24 GPIOR23 GPIOR22 GPIOR21 GPIOR20 GPIOR2

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value00000000

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5. System Clock

General I/O

Modules

ADC CPU Core RAM

clk

I/O

AVR Clock

Control Unit

clk

CPU

Flash and EEPROM

clk

FLASH

clk

ADC

Source Clock

Watchdog Timer

Watchdog

Oscillator

Reset Logic

Clock Multiplexer

Watchdog Clock

Calibrated RC

Oscillator

(Crystal

Oscillator)

External Clock

Fast Peripherals

PLL

CLK

PLL

Multiplexer

PLL Input

5.1 Clock Systems and their Distribution

Figure 5-1 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 unused modules can be halted by using different sleep modes, as described in “Power Management and

Sleep Modes” on page 40. The clock systems are detailed below.

Figure 5-1. Clock Distribution

Atmel ATmega16/32/64/M1/C1

5.1.1 CPU Clock – clk

5.1.2 I/O Clock – clk

CPU

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

The I/O clock is used by the majority of the I/O modules, like Timer/Counters, SPI, UART. The I/O clock is also used by the External Interrupt module, but note that some external interrupts are detected by asynchronous logic, allowing such interrupts to be detected even if the I/O clock is halted.

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5.1.3 Flash Clock – clk

The Flash clock controls operation of the Flash interface. The Flash clock is usually active simultaneously with the CPU clock.

FLASH

5.1.4 PLL Clock – clk

5.1.5 ADC Clock – clk

5.2 Clock Sources

PLL

The PLL clock allows the fast peripherals to be clocked directly from a 64/32MHz clock. A 16MHz clock is also derived for the CPU.

ADC

The ADC is provided with a dedicated clock domain. This allows halting the CPU and I/O clocks in order to reduce noise generated by digital circuitry. This gives more accurate ADC conversion results.

The device has the following clock source options, selectable by Flash Fuse bits as illustrated Table 5-1. The clock from the selected source is input to the AVR clock generator, and routed to the appropriate modules.

Table 5-1. Device Clocking Options Select

Device Clocking Option

External Crystal/Ceramic Resonator Ext Osc RC Osc 1111 - 1000

PLL output divided by 4 : 16MHz / PLL driven by External Crystal/Ceramic Resonator

(1)

System Clock PLL Input CKSEL3..0

Ext Osc Ext Osc 0100

PLL output divided by 4 : 16MHz / PLL driven by External Crystal/Ceramic Resonator

Reserved N/A N/A 0110

Reserved N/A N/A 0111

PLL output divided by 4 : 16MHz PLL / 4 RC Osc 0011

Calibrated Internal RC Oscillator RC Osc RC Osc 0010

PLL output divided by 4 : 16MHz / PLL driven by External clock

External Clock Ext Clk RC Osc 0000

Note: 1. For all fuses “1” means unprogrammed while “0” means programmed.

2. Ext Osc : External Osc

3. RC Osc : Internal RC Oscillator

4. Ext Clk : External Clock Input

PLL / 4 Ext Osc 0101

PLL / 4 Ext Clk 0001

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 starting normal operation. The Watchdog Oscillator is used for timing this real-time part of the start-up time. The number of WDT Oscillator cycles used for each time-out is shown in Table

5-2. The frequency of the Watchdog Oscillator is voltage dependent as shown in “Watchdog Oscillator Frequency versus V

” on page 342.

Atmel ATmega16/32/64/M1/C1

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Table 5-2. Number of Watchdog Oscillator Cycles

XTAL2

XTAL1

GND

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)

5.3 Default Clock Source

The device is shipped with CKSEL = “0010”, SUT = “10”, and CKDIV8 programmed. The default clock source setting is the Internal RC Oscillator with longest start-up 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.

5.4 Low Power Crystal Oscillator

XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be configured for use as an On-chip Oscillator, as shown in Figure 5-2. Either a quartz crystal or a ceramic resonator may be used.

This Crystal Oscillator is a low power oscillator, with reduced voltage swing on the XTAL2 output. It gives the lowest power consumption, but is not capable of driving other clock inputs.

Atmel ATmega16/32/64/M1/C1

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 5-3. For ceramic resonators, the capacitor values given by the manufacturer should be used. For more information on how to choose capacitors and other details on Oscillator operation, refer to the Multi-purpose Oscillator Application Note.

Figure 5-2. Crystal Oscillator Connections

7647H–AVR–03/12

The Oscillator can operate in three different modes, each optimized for a specific frequency range. The operating mode is selected by the fuses CKSEL3..1 as shown in Table 5-3.

Table 5-3. Crystal Oscillator Operating Modes

Recommended Range for Capacitors C1 and

CKSEL3..1 Frequency Range (MHz)

(1)

100

0.4 - 0.9 –

C2 for Use with Crystals (pF)

101 0.9 - 3.0 12 - 22

110 3.0 - 8.0 12 - 22

111 8.0 -16.0 12 - 22

Notes: 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

5-4.

Table 5-4. Start-up Times for the Oscillator Clock Selection

Start-up Time from

Power-down and

CKSEL0 SUT1..0

000 258 CK

001 258 CK

010 1K CK

011 1K CK

100 1K CK

Power-save

(1)

(2)

1 01 16K CK 14CK

1 10 16K CK 14CK + 4.1 ms

1 11 16K CK 14CK + 65 ms

Additional Delay

from Reset

(VCC = 5.0V) Recommended Usage

14CK + 4.1 ms

14CK + 65 ms

14CK

14CK + 4.1 ms

14CK + 65 ms

Ceramic resonator, fast rising power

Ceramic resonator, slowly rising power

Ceramic resonator, BOD enabled

Ceramic resonator, fast rising power

Ceramic resonator, slowly rising power

Crystal Oscillator, BOD enabled

Crystal Oscillator, fast rising power

Crystal Oscillator, slowly rising power

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 frequency of the device, and if frequency stability at start-up is not important for the application.

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5.5 Calibrated Internal RC Oscillator

By default, the Internal RC OScillator provides an approximate 8.0MHz clock. Though voltage and temperature dependent, this clock can be very accurately calibrated by the user. The device is shipped with the CKDIV8 Fuse programmed. See “System Clock Prescaler” on page 37 for more details.

This clock may be selected as the system clock by programming the CKSEL Fuses as shown in

Table 5-1 on page 30. If selected, it will operate with no external components. During reset,

hardware loads the pre-programmed calibration value into the OSCCAL Register and thereby automatically calibrates the RC Oscillator. The accuracy of this calibration is shown as Factory calibration in Table 26-1 on page 319.

By changing the OSCCAL register from SW, see “Oscillator Calibration Register – OSCCAL” on

page 34, it is possible to get a higher calibration accuracy than by using the factory calibration.

The accuracy of this calibration is shown as User calibration in “Clock Characteristics” on page

319.

When this Oscillator is used as the chip clock, the Watchdog Oscillator will still be used for the Watchdog Timer and for the Reset Time-out. For more information on the pre-programmed calibration value, see the section.

Atmel ATmega16/32/64/M1/C1

Table 5-5. Internal Calibrated RC Oscillator Operating Modes

Frequency Range (MHz) CKSEL3..0

7.3 - 8.1 0010

Notes: 1. The device is shipped with this option selected.

2. If 8MHz frequency exceeds the specification of the device (depends on V Fuse can be programmed in order to divide the internal frequency by 8.

(1)(2)

), the CKDIV8

When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in

Table 5-6 on page 33.

Table 5-6. Start-up times for the internal calibrated RC Oscillator clock selection

Start-up Time from

Power Conditions

BOD enabled 6 CK 14CK

Fast rising power 6 CK 14CK + 4.1 ms 01

Slowly rising power 6 CK 14CK + 65 ms

Note: 1. If the RSTDISBL fuse is programmed, this start-up time will be increased to

14CK + 4.1 ms to ensure programming mode can be entered.

The device is shipped with this option selected.

Power-down and Power-save

Reserved 11

Additional Delay from

Reset (VCC = 5.0V) SUT1..0

(1)

(2)

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5.5.1 Oscillator Calibration Register – OSCCAL

Bit 76543210

CAL7 CAL6 CAL5 CAL4 CAL3 CAL2 CAL1 CAL0 OSCCAL

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value Device Specific Calibration Value

• Bits 7..0 – CAL7..0: Oscillator Calibration Value

The Oscillator Calibration Register is used to trim the Calibrated Internal RC Oscillator to remove process variations from the oscillator frequency. The factory-calibrated value is automatically written to this register during chip reset, giving an oscillator frequency of 8.0MHz at 25°C. The application software can write this register to change the oscillator frequency. The oscillator can be calibrated to any frequency in the range 7.3 - 8.1MHz within ±1% accuracy. Calibration outside that range is not guaranteed.

Note that this oscillator is used to time EEPROM and Flash write accesses, and these write times will be affected accordingly. If the EEPROM or Flash are written, do not calibrate to more than 8.8MHz. Otherwise, the EEPROM or Flash write may fail.

The CAL7 bit determines the range of operation for the oscillator. Setting this bit to 0 gives the lowest frequency range, setting this bit to 1 gives the highest frequency range. The two frequency ranges are overlapping, in other words a setting of OSCCAL = 0x7F gives a higher frequency than OSCCAL = 0x80.

The CAL6..0 bits are used to tune the frequency within the selected range. A setting of 0x00 gives the lowest frequency in that range, and a setting of 0x7F gives the highest frequency in the range. Incrementing CAL6..0 by 1 will give a frequency increment of less than 2% in the frequency range 7.3 - 8.1MHz.

5.6 PLL

5.6.1 Internal PLL

The internal PLL in ATmega16/32/64/M1/C1 generates a clock frequency that is 64x multiplied from its nominal 1MHz input. The source of the 1MHz PLL input clock can be:

• the output of the internal RC Oscillator divided by 8

• the output of the Crystal Oscillator divided by 8

• the external clock divided by 8

See the Figure 5-3 on page 35.

When the PLL is locked on the RC Oscillator, adjusting the RC Oscillator via OSCCAL Register, will also modify the PLL clock output. However, even if the possibly divided RC Oscillator is taken to a higher frequency than 8MHz, the PLL output clock frequency saturates at 70MHz (worst case) and remains oscillating at the maximum frequency. It should be noted that the PLL in this case is not locked any more with its 1MHz source clock.

Therefore it is recommended not to take the OSCCAL adjustments to a higher frequency than 8MHz in order to keep the PLL in the correct operating range.

The internal PLL is enabled only when the PLLE bit in the register PLLCSR is set. The bit PLOCK from the register PLLCSR is set when PLL is locked.

Both internal 8MHz RC Oscillator, Crystal Oscillator and PLL are switched off in Power-down and Standby sleep modes.03/12

Atmel ATmega16/32/64/M1/C1

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Atmel ATmega16/32/64/M1/C1

8 MHz

RC OSCILLATOR

OSCCAL

XTAL1 XTAL2

OSCILLATORS

DIVIDE

BY 8

DIVIDE

BY 2

PLL

64x

PLLE

Lock

Detector

PLOCK

SOURCE

PLLF

DIVIDE

BY 4

CLK

PLL

CKSEL3..0

Table 5-7. Start-up Times when the PLL is selected as system clock

CKSEL

3..0 SUT1..0

0011

RC Osc

0101

Ext Osc

0001

Ext Clk

1. This value do not provide a proper restart ; do not use PD in this clock scheme

2. This value do not provide a proper restart ; do not use PD in this clock scheme

3. This value do not provide a proper restart ; do not use PD in this clock scheme

Figure 5-3. PLL Clocking System

Start-up Time from Power-down

and Power-save

Additional Delay from Reset

(VCC = 5.0V)

00 1K CK 14CK

01 1K CK 14CK + 4 ms

10 1K CK 14CK + 64 ms

11 16K CK 14CK

00 1K CK 14CK

01 1K CK 14CK + 4 ms

10 16K CK 14CK + 4 ms

11 16K CK 14CK + 64 ms

00 6 CK

01 6 CK

10 6 CK

(1)

(2)

(3)

14CK

14CK + 4 ms

14CK + 64 ms

11 Reserved

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5.6.2 PLL Control and Status Register – PLLCSR

XTAL2

XTAL1

GND

External

Clock

Signal

Bit 76543210 $29 ($29) –––––PLLFPLLEPLOCKPLLCSR Read/Write R R R R R R/W R/W R Initial Value0000000/10

• Bit 7..3 – Res: Reserved Bits

These bits are reserved bits in the ATmega16/32/64/M1/C1 and always read as zero.

• Bit 2 – PLLF: PLL Factor

The PLLF bit is used to select the division factor of the PLL. If PLLF is set, the PLL output is 64MHz. If PLLF is clear, the PLL output is 32MHz.

• Bit 1 – PLLE: PLL Enable

When the PLLE is set, the PLL is started and if not yet started the internal RC Oscillator is started as PLL reference clock. If PLL is selected as a system clock source the value for this bit is always 1.

• Bit 0 – PLOCK: PLL Lock Detector

When the PLOCK bit is set, the PLL is locked to the reference clock, and it is safe to enable CLK

for Fast Peripherals. After the PLL is enabled, it takes about 100 µs for the PLL to lock.

PLL

5.7 128 kHz Internal Oscillator

5.8 External Clock

The 128 kHz internal Oscillator is a low power Oscillator providing a clock of 128 kHz. The frequency is nominal at 3V and 25°C. This clock is used by the Watchdog Oscillator.

To drive the device from an external clock source, XTAL1 should be driven as shown in Figure

5-4. To run the device on an external clock, the CKSEL Fuses must be programmed to “0000”.

Figure 5-4. External Clock Drive Configuration

Table 5-8. External Clock Frequency

CKSEL3..0 Frequency Range

0000 0 - 16MHz

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Atmel ATmega16/32/64/M1/C1

When this clock source is selected, start-up times are determined by the SUT Fuses as shown in

Table 5-9.

Table 5-9. Start-up Times for the External Clock Selection

SUT1..0

00 6 CK 14CK BOD enabled

01 6 CK 14CK + 4.1 ms Fast rising power

10 6 CK 14CK + 65 ms Slowly rising power

11 Reserved

When applying an external clock, it is required to avoid sudden changes in the applied clock frequency 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

37 for details.

5.9 Clock Output Buffer

When the CKOUT Fuse is programmed, the system Clock will be output on CLKO. 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 I/O pin will be overridden when the fuse is programmed. Any clock source, including internal RC Oscillator, can be selected when CLKO serves as clock output. If the System Clock Prescaler is used, it is the divided system clock that is output (CKOUT Fuse programmed).

Start-up Time from

Power-down and Power-save

Additional Delay from

Reset (VCC = 5.0V) Recommended Usage

5.10 System Clock Prescaler

The ATmega16/32/64/M1/C1 system clock can be divided by setting the Clock Prescale Register – CLKPR. This feature can be used to decrease 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. clk are divided by a factor as shown in Table 5-10.

When switching between prescaler settings, the System Clock Prescaler ensures that no glitches occurs in the clock system. It also ensures 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 the other 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.

I/O

, clk

ADC

, clk

, and clk

CPU

FLASH

7647H–AVR–03/12

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.

Interrupts must be disabled when changing prescaler setting to make sure the write procedure is not interrupted.

5.10.1 Clock Prescaler Register – CLKPR

Bit 76543210

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

• Bit 7 – CLKPCE: Clock Prescaler Change Enable

The CLKPCE bit must be written to logic one to enable change of the CLKPS bits. The CLKPCE bit is only updated when the other bits in CLKPR are simultaniosly written to zero. CLKPCE is cleared by hardware four cycles after it is written or when CLKPS bits are written. Rewriting the CLKPCE bit within this time-out period does neither extend the time-out period, nor clear the CLKPCE bit.

• 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 synchronous peripherals is reduced when a division factor is used. The division factors are given in

Table 5-10.

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 operating 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 selcted 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.

Atmel ATmega16/32/64/M1/C1

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Atmel ATmega16/32/64/M1/C1

Table 5-10. Clock Prescaler Select

CLKPS3 CLKPS2 CLKPS1 CLKPS0 Clock Division Factor

0000 1

0001 2

0010 4

0011 8

0100 16

0101 32

0110 64

0111 128

1000 256

1001 Reserved

1010 Reserved

1011 Reserved

1100 Reserved

1101 Reserved

1110 Reserved

1111 Reserved

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6. 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 consumption to the application’s requirements.

To enter any of the five sleep modes, the SE bit in SMCR must be written to logic one and a SLEEP instruction must be executed. The SM2, SM1, and SM0 bits in the SMCR Register select which sleep mode (Idle, ADC Noise Reduction, Power-down, Power-save, or Standby) will be activated by the SLEEP instruction. See Table 6-1 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 routine, 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 5-1 on page 29 presents the different clock systems in the ATmega16/32/64/M1/C1, and

their distribution. The figure is helpful in selecting an appropriate sleep mode.

6.1 Sleep Mode Control Register

6.1.1 Sleep Mode Control Register – SMCR

The Sleep Mode Control Register contains control bits for power management.

Bit 76543210

– – – – SM2 SM1 SM0 SE SMCR

Read/Write R R R R R/W R/W R/W R/W Initial Value 00000000

• Bits 3..1 – SM2..0: Sleep Mode Select Bits 2, 1, and 0

These bits select between the five available sleep modes as shown in Table 6-1.

Table 6-1. Sleep Mode Select

SM2 SM1 SM0 Sleep Mode

000Idle

0 0 1 ADC Noise Reduction

010Power-down

011Reserved

100Reserved

101Reserved

110Standby

111Reserved

Note: 1. Standby mode is only recommended for use with external crystals or resonators.

(1)

• Bit 1 – 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.

Atmel ATmega16/32/64/M1/C1

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6.2 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 SPI, UART, Analog Comparator, ADC, Timer/Counters, Watchdog, and the interrupt system to continue operating. This sleep mode basically halt clk and clk

, while allowing the other clocks to run.

FLASH

Idle mode enables the MCU to wake up from external triggered interrupts as well as internal ones like the Timer Overflow and UART 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. If the ADC is enabled, a conversion starts automatically when this mode is entered.

6.3 ADC Noise Reduction Mode

When the SM2..0 bits are written to 001, the SLEEP instruction makes the MCU enter ADC Noise Reduction mode, stopping the CPU but allowing the ADC, the External Interrupts, Timer/Counter (if their clock source is external - T0 or T1) and the Watchdog to continue operating (if enabled). This sleep mode basically halts clk the other clocks to run.

This improves the noise environment for the ADC, enabling higher resolution measurements. If the ADC is enabled, a conversion starts automatically when this mode is entered. Apart from the ADC Conversion Complete interrupt, only an External Reset, a Watchdog Reset, a Brown-out Reset, a Timer/Counter interrupt, an SPM/EEPROM ready interrupt, an External Level Interrupt on INT3:0 can wake up the MCU from ADC Noise Reduction mode.

Atmel ATmega16/32/64/M1/C1

CPU

I/O

, clk

CPU

, and clk

, while allowing

FLASH

6.4 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, a PSC Interrupt, an External Level Interrupt on INT3:0 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 82 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 30.

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6.5 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 Oscillator is kept running. From Standby mode, the device wakes up in six clock cycles.

Table 6-2. Active Clock Domains and Wake-up Sources in the Different Sleep Modes.

Oscillator

Active Clock Domains

s Wake-up Sources

Sleep Mode

Idle X X X X X X X X X X

ADC Noise Reduction

Power-do wn

Standby

Notes: 1. Only recommended with external crystal or resonator selected as clock source.

(1)

2. Only level interrupt.

6.6 Power Reduction Register

The Power Reduction Register, PRR, provides a method to stop the clock to individual peripherals to reduce power consumption. The current state of the peripheral is frozen and the I/O registers can not be read or written. Resources used by the peripheral when stopping the clock will remain occupied, hence the peripheral should in most cases be disabled before stopping the clock. Waking up a module, which is done by clearing the bit in PRR, puts the module in the same state as before shutdown.

A full predictible behaviour of a peripheral is not guaranteed during and after a cycle of stopping and starting of its clock. So its recommended to stop a peripheral before stopping its clock with PRR register.

CPU

clk

FLASH

clk

XX X X

ADC

clk

PLL

clk

Main Clock

Source Enabled

INT3..0

(2)

PSC

SPM/EEPROM

XXXX

ADC

Ready

WDT

OtherI/O

Module shutdown can be used in Idle mode and Active mode to significantly reduce the overall power consumption. In all other sleep modes, the clock is already stopped.

Atmel ATmega16/32/64/M1/C1

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6.6.1 Power Reduction Register - PRR

Bit 765432 1 0

- PRCAN PRPSC

Read/Write R R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0

• Bit 7 - Res: Reserved Bit

This bit is unused bit in the ATmega16/32/64/M1/C1, and will always read as zero.

• Bit 6 - PRCAN: Power Reduction CAN

Writing a logic one to this bit reduces the consumption of the CAN by stopping the clock to this module. When waking up the CAN again, the CAN should be re initialized to ensure proper operation.

• Bit 5 - PRPSC: Power Reduction PSC

Writing a logic one to this bit reduces the consumption of the PSC by stopping the clock to this module. When waking up the PSC again, the PSC should be re initialized to ensure proper operation.

• Bit 4 - PRTIM1: Power Reduction Timer/Counter1

Writing a logic one to this bit reduces the consumption of the Timer/Counter1 module. When the Timer/Counter1 is enabled, operation will continue like before the setting of this bit.

• Bit 3 - PRTIM0: Power Reduction Timer/Counter0

Atmel ATmega16/32/64/M1/C1

PRTIM1 PRTIM0 PRSPI PRLIN PRADC PRR

Writing a logic one to this bit reduces the consumption of the Timer/Counter0 module. When the Timer/Counter0 is enabled, operation will continue like before the setting of this bit.

• Bit 2 - PRSPI: Power Reduction Serial Peripheral Interface

Writing a logic one to this bit reduces the consumption of the Serial Peripheral Interface by stopping the clock to this module. When waking up the SPI again, the SPI should be re initialized to ensure proper operation.

• Bit 1 - PRLIN: Power Reduction LIN

Writing a logic one to this bit reduces the consumption of the UART controller by stopping the clock to this module. When waking up the UART controller again, the UART controller should be re initialized to ensure proper operation.

• Bit 0 - PRADC: Power Reduction ADC

Writing a logic one to this bit reduces the consumption of the ADC by stopping the clock to this module. The ADC must be disabled before using this function. The analog comparator cannot use the ADC input MUX when the clock of ADC is stopped.

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6.7 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.

6.7.1 Analog to Digital Converter

If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should be disabled before entering any sleep mode. When the ADC is turned off and on again, the next conversion will be an extended conversion. Refer to “Analog to Digital Converter - ADC” on

page 230 for details on ADC operation.

6.7.2 Analog Comparator

When entering Idle mode, the Analog Comparator should be disabled if not used. When entering ADC Noise Reduction mode, the Analog Comparator should be disabled. In other sleep modes, the Analog Comparator is automatically disabled. However, if the Analog Comparator 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, independent of sleep mode. Refer to “Analog Comparator” on page 262 for details on how to configure the Analog Comparator.

6.7.3 Brown-out Detector

If the Brown-out Detector is not needed by 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 49 for details on how to configure the Brown-out Detector.

6.7.4 Internal Voltage Reference

The Internal Voltage Reference will be enabled when needed by the Brown-out Detection, the Analog Comparator or the ADC. If these modules are disabled as described in the sections above, the internal 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 Volt-

age Reference” on page 51 for details on the start-up time.

6.7.5 Watchdog Timer

If the Watchdog Timer is not needed in the application, the 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 consumption. Refer to “Watchdog Timer” on page 52 for details on how to configure the Watchdog Timer.

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

6.7.6 Port Pins

When entering a sleep mode, all port pins should be configured to use minimum power. The most important is then to ensure that no pins drive resistive loads. In sleep modes where both the I/O clock (clk 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 “I/O-Ports” on page 62 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 V

/2, the input buffer will use excessive power.

For analog input pins, the digital input buffer should be disabled at all times. An analog signal level close to V input buffers can be disabled by writing to the Digital Input Disable Registers (DIDR1 and DIDR0). Refer to “Digital Input Disable Register 1– DIDR1” and “Digital Input Disable Register 0 – DIDR0” on page 269 and page 249 for details.

6.7.7 On-chip Debug System

If the On-chip debug system is enabled by OCDEN Fuse and the chip enter sleep mode, the main clock source is enabled, and hence, always consumes power. In the deeper sleep modes, this will contribute significantly to the total current consumption.

Atmel ATmega16/32/64/M1/C1

) and the ADC clock (clk

I/O

/2 on an input pin can cause significant current even in active mode. Digital

) are stopped, the input buffers of the device will

ADC

7647H–AVR–03/12

7. System Control and Reset

7.1 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 7-1 on page 47 shows the reset logic. Table 7-1 on page 47 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 SUT and CKSEL Fuses. The different selections for the delay period are presented in “Clock Sources” on page 30.

7.2 Reset Sources

The ATmega16/32/64/M1/C1 has four sources of reset:

• Power-on Reset. The MCU is reset when the supply voltage is below the Power-on Reset threshold (V

• External Reset. The MCU is reset when a low level is present on the RESET 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 V Reset threshold (V

POT

) and the Brown-out Detector is enabled.

BOT

pin for longer

is below the Brown-out

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

Figure 7-1. Reset Logic

MCU Status

Brown-out

Reset Circuit

BODLEVEL [2..0]

Delay Counters

CKSEL[3:0]

TIMEOUT

WDRF

BORF

EXTRF

PORF

DATA BU S

Clock

Generator

Spike

Filter

Pull-up Resistor

Watchdog

Oscillator

SUT[1:0]

Power-on Reset

Circuit

Atmel ATmega16/32/64/M1/C1

7.2.1 Power-on Reset

Table 7-1. Reset Characteristics

Symbol Parameter Min Typ Max Units

Power-on Reset Threshold Voltage (rising) 1.1 1.4 1.7 V

POT

PORMAX

PORMIN

CCRR

RST

Note: 1. Before rising, the supply has to be between V

A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detection level

Power-on Reset Threshold Voltage (falling)

VCC Max. start voltage to ensure internal Power-on Reset signal

VCC Min. start voltage to ensure internal Power-on Reset signal

VCC Rise Rate to ensure Power-on Reset 0.01 V/ms

RESET Pin Threshold Voltage 0.1 V

is defined in Table 7-1. The POR is activated whenever V

(1)

PORMIN

0.8 0.9 1.6 V

0.4 V

-0.1 V

and V

PORMAX

is below the detection level. The

0.9V

to ensure a Reset.

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 V when V

decreases below the detection level.

rise. The RESET signal is activated again, without any delay,

7647H–AVR–03/12

Figure 7-2. MCU Start-up, RESET Tied to VCC

RESET

TIM E-OUT

INTERNAL

RESET

TOU T

RST

CCRR

PORMIN

PORMAX

RESET

TIME-OUT

INTERNAL

RESET

TOUT

POT

RST

7.2.2 External Reset

Figure 7-3. MCU Start-up, RESET

An External Reset is generated by a low level on the RESET

Extended Externally

pin. Reset pulses longer than the minimum pulse width (see Table 7-1) 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 – V the Time-out period – t

TOUT –

– on its positive edge, the delay counter starts the MCU after

RST

has expired.

Figure 7-4. External Reset During Operation

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

7.2.3 Brown-out Detection

ATmega16/32/64/M1/C1 has an On-chip Brown-out Detection (BOD) circuit for monitoring the V

level during 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 V V

BOT

Table 7-2. BODLEVEL Fuse Coding

+ V

HYST

/2 and V

BOT-

= V

BOT

Atmel ATmega16/32/64/M1/C1

- V

HYST

/2.

(1)(2)

BOT+

BODLEVEL 2..0 Fuses Typ V

BOT

Units

111 Disabled

110 4.5 V

011 4.4 V

100 4.3 V

010 4.2 V

001 2.8 V

101 2.7 V

000 2.6 V

Notes: 1. V

may be below nominal minimum operating voltage for some devices. For devices where

BOT

this is the case, the device is tested down to V

= V

during the production test. This guar-

BOT

antees that a Brown-Out Reset will occur before VCC drops to a voltage where correct operation of the microcontroller is no longer guaranteed. The test is performed using BODLEVEL = 010 for Low Operating Voltage and BODLEVEL = 101 for High Operating Voltage .

2. Values are guidelines only.

Table 7-3. Brown-out Characteristics

(1)

Symbol Parameter Min. Typ. Max. Units

BOD

HYST

Brown-out Detector Hysteresis 80 mV

Min Pulse Width on Brown-out Reset 2 µs

7647H–AVR–03/12

Notes: 1. Values are guidelines only.

When the BOD is enabled, and VCC decreases to a value below the trigger level (V

7-5 on page 50), the Brown-out Reset is immediately activated. When V

trigger level (V Time-out period t

The BOD circuit will only detect a drop in V ger than t

given in Table 7-3.

BOD

in Figure 7-5 on page 50), the delay counter starts the MCU after the

BOT+

has expired.

TOUT

if the voltage stays below the trigger level for lon-

increases above the

in Figure

BOT-

7.2.4 Watchdog Reset

RESET

TIME-OUT

INTERNAL

RESET

BOT-

BOT+

TOUT

Figure 7-5. Brown-out Reset During Operation

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 t

TOUT

. Refer to

page 52 for details on operation of the Watchdog Timer.

Figure 7-6. Watchdog Reset During Operation

7.2.5 MCU Status Register – MCUSR

The MCU Status Register provides information on which reset source caused an MCU reset.

Bit 76543210

Read/Write R R R R R/W R/W R/W R/W Initial Value 0 0 0 0 See Bit Description

• 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.

• 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.

Atmel ATmega16/32/64/M1/C1

– – – – WDRF BORF EXTRF PORF MCUSR

7647H–AVR–03/12

• 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 MCUSR 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.

7.3 Internal Voltage Reference

ATmega16/32/64/M1/C1 features an internal bandgap reference. This reference is used for Brown-out DetectionDetection, and it can be used as an input to the Analog Comparators or the ADC. The V internal bandgap reference.

7.3.1 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 7-4. To save power, the reference is not always turned on. The reference is on during the following situations:

1. When the BOD is enabled (by programming the BODLEVEL [2..0] Fuse).

2. When the bandgap reference is connected to the Analog Comparator (by setting the

ACBG bit in ACSR).

3. When the ADC is enabled.

4. When the DAC is enabled.

2.56V reference to the ADC, DAC or Analog Comparators is generated from the

REF

Atmel ATmega16/32/64/M1/C1

Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC or the DAC, the user must always allow the reference to start up before the output from the Analog Comparator or ADC or DAC is used. To reduce power consumption in Power-down mode, the user can avoid the three conditions above to ensure that the reference is turned off before entering Power-down mode.

7.3.2 Voltage Reference Characteristics

Table 7-4. Internal Voltage Reference Characteristics

Symbol Parameter Condition Min. Typ. Max. Units

Note: 1. Values are guidelines only.

Bandgap reference voltage 1.1 V

Bandgap reference start-up time 40 µs

Bandgap reference current consumption

(1)

15 µA

7647H–AVR–03/12

7.4 Watchdog Timer

128 KHz

OSCILLATOR

MCU RESET

INTERRUPT

WDIE

WDIF

OSC/2K

OSC/4K

OSC/8K

WDP3

ATmega16/32/64/M1/C1 has an Enhanced Watchdog Timer (WDT). The main features are:

•

• 3 Operating modes

• Selectable Time-out period from 16ms to 8s

• Possible Hardware fuse Watchdog always on (WDTON) for fail-safe mode

Figure 7-7. Watchdog Timer

Clocked from separate On-chip Oscillator

– Interrupt – System Reset – Interrupt and System Reset

The Watchdog Timer (WDT) is a timer counting cycles of a separate on-chip 128 kHz oscillator. The WDT gives an interrupt or a system reset when the counter reaches a given time-out value. In normal operation mode, it is required that the system uses the WDR - Watchdog Timer Reset

- instruction to restart the counter before the time-out value is reached. If the system doesn't restart the counter, an interrupt or system reset will be issued.

In Interrupt mode, the WDT gives an interrupt when the timer expires. This interrupt can be used to wake the device from sleep-modes, and also as a general system timer. One example is to limit the maximum time allowed for certain operations, giving an interrupt when the operation has run longer than expected. In System Reset mode, the WDT gives a reset when the timer expires. This is typically used to prevent system hang-up in case of runaway code. The third mode, Interrupt and System Reset mode, combines the other two modes by first giving an interrupt and then switch to System Reset mode. This mode will for instance allow a safe shutdown by saving critical parameters before a system reset.

The “Watchdog Timer Always On” (WDTON) fuse, if programmed, will force the Watchdog Timer to System Reset mode. With the fuse programmed the System Reset mode bit (WDE) and Interrupt mode bit (WDIE) are locked to 1 and 0 respectively. To further ensure program security, alterations to the Watchdog set-up must follow timed sequences. The sequence for clearing WDE and changing time-out configuration is as follows:

1. In the same operation, write a logic one to the Watchdog change enable bit (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, write the WDE and Watchdog prescaler bits (WDP) as

desired, but with the WDCE bit cleared. This must be done in one operation.

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

Atmel ATmega16/32/64/M1/C1

The following code example shows one assembly and one C function for turning off the Watchdog Timer. The example assumes that interrupts are controlled (e.g. by disabling interrupts globally) so that no interrupts will occur during the execution of these functions.

Assembly Code Example

WDT_off:

; Turn off global interrupt

cli

; Reset Watchdog Timer

wdr

; Clear WDRF in MCUSR

in r16, MCUSR andi r16, (0xff & (0<<WDRF)) out MCUSR, r16

; Write logical one to WDCE and WDE ; Keep old prescaler setting to prevent unintentional time-out

lds r16, WDTCSR ori r16, (1<<WDCE) | (1<<WDE) sts WDTCSR, r16

; Turn off WDT

ldi r16, (0<<WDE) sts WDTCSR, r16

; Turn on global interrupt

sei ret

C Code Example

(1)

void WDT_off(void) {

__disable_interrupt(); __watchdog_reset(); /* Clear WDRF in MCUSR */ MCUSR &= ~(1<<WDRF); /* Write logical one to WDCE and WDE */ /* Keep old prescaler setting to prevent unintentional time-out */ WDTCSR |= (1<<WDCE) | (1<<WDE); /* Turn off WDT */ WDTCSR = 0x00; __enable_interrupt();

}

Note: 1. The example code assumes that the part specific header file is included.

Note: If the Watchdog is accidentally enabled, for example by a runaway pointer or brown-out condition, the device will be reset and the Watchdog Timer will stay enabled. If the code is not set up to handle the Watchdog, this might lead to an eternal loop of time-out resets. To avoid this situation, the application software should always clear the Watchdog System Reset Flag (WDRF) and the WDE control bit in the initialisation routine, even if the Watchdog is not in use.

7647H–AVR–03/12

The following code example shows one assembly and one C function for changing the time-out value of the Watchdog Timer.

Assembly Code Example

WDT_Prescaler_Change:

; Turn off global interrupt

cli

; Reset Watchdog Timer

wdr

; Start timed sequence

lds r16, WDTCSR ori r16, (1<<WDCE) | (1<<WDE) sts WDTCSR, r16

; -- Got four cycles to set the new values from here ; Set new prescaler(time-out) value = 64K cycles (~0.5 s)

ldi r16, (1<<WDE) | (1<<WDP2) | (1<<WDP0) sts WDTCSR, r16

; -- Finished setting new values, used 2 cycles ; Turn on global interrupt

sei ret

C Code Example

(1)

void WDT_Prescaler_Change(void) {

__disable_interrupt(); __watchdog_reset(); /* Start timed equence */ WDTCSR |= (1<<WDCE) | (1<<WDE); /* Set new prescaler(time-out) value = 64K cycles (~0.5 s) */ WDTCSR = (1<<WDE) | (1<<WDP2) | (1<<WDP0); __enable_interrupt();

}

Note: 1. The example code assumes that the part specific header file is included.

Note: The Watchdog Timer should be reset before any change of the WDP bits, since a change in the WDP bits can result in a time-out when switching to a shorter time-out period;

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

7.4.1 Watchdog Timer Control Register - WDTCSR

Bit 76543210

WDIF WDIE WDP3 WDCE WDE WDP2 WDP1 WDP0 WDTCSR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value0000X000

• Bit 7 - WDIF: Watchdog Interrupt Flag

This bit is set when a time-out occurs in the Watchdog Timer and the Watchdog Timer is configured for interrupt. WDIF is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, WDIF is cleared by writing a logic one to the flag. When the I-bit in SREG and WDIE are set, the Watchdog Time-out Interrupt is executed.

• Bit 6 - WDIE: Watchdog Interrupt Enable

When this bit is written to one and the I-bit in the Status Register is set, the Watchdog Interrupt is enabled. If WDE is cleared in combination with this setting, the Watchdog Timer is in Interrupt Mode, and the corresponding interrupt is executed if time-out in the Watchdog Timer occurs.

If WDE is set, the Watchdog Timer is in Interrupt and System Reset Mode. The first time-out in the Watchdog Timer will set WDIF. Executing the corresponding interrupt vector will clear WDIE and WDIF automatically by hardware (the Watchdog goes to System Reset Mode). This is useful for keeping the Watchdog Timer security while using the interrupt. To stay in Interrupt and System Reset Mode, WDIE must be set after each interrupt. This should however not be done within the interrupt service routine itself, as this might compromise the safety-function of the Watchdog System Reset mode. If the interrupt is not executed before the next time-out, a System Reset will be applied.

Atmel ATmega16/32/64/M1/C1

Table 7-5. Watchdog Timer Configuration

WDTON

Note: 1. For the WDTON Fuse “1” means unprogrammed while “0” means programmed.

(1)

0 0 0 Stopped None

0 0 1 Interrupt Mode Interrupt

0 1 0 System Reset Mode Reset

011

1 x x System Reset Mode Reset

WDE WDIE Mode Action on Time-out

Interrupt and System Reset Mode

Interrupt, then go to System Reset Mode

• Bit 4 - WDCE: Watchdog Change Enable

This bit is used in timed sequences for changing WDE and prescaler bits. To clear the WDE bit, and/or change the prescaler bits, WDCE must be set.

Once written to one, hardware will clear WDCE after four clock cycles.

• Bit 3 - WDE: Watchdog System Reset Enable

WDE is overridden by WDRF in MCUSR. This means that WDE is always set when WDRF is set. To clear WDE, WDRF must be cleared first. This feature ensures multiple resets during conditions causing failure, and a safe start-up after the failure.

• Bit 5, 2..0 - WDP3..0: Watchdog Timer Prescaler 3, 2, 1 and 0

7647H–AVR–03/12

The WDP3..0 bits determine the Watchdog Timer prescaling when the Watchdog Timer is running. The different prescaling values and their corresponding time-out periods are shown in

Table 7-6 on page 56.

Table 7-6. Watchdog Timer Prescale Select

Number of WDT Oscillator

WDP3 WDP2 WDP1 WDP0

0000 2K (2048) cycles 16 ms

0001 4K (4096) cycles 32 ms

0010 8K (8192) cycles 64 ms

0011 16K (16384) cycles 0.125 s

0100 32K (32768) cycles 0.25 s

0101 64K (65536) cycles 0.5 s

0110 128K (131072) cycles 1.0 s

0111 256K (262144) cycles 2.0 s

1000 512K (524288) cycles 4.0 s

10011024K (1048576) cycles 8.0 s

1010

1011

1100

1101

1110

1111

Cycles

Reserved

Typical Time-out at

VCC = 5.0V

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

8. Interrupts

This section describes the specifics of the interrupt handling as performed in ATmega16/32/64/M1/C1. For a general explanation of the AVR interrupt handling, refer to

“Reset and Interrupt Handling” on page 17.

8.1 Interrupt Vectors in ATmega16/32/64/M1/C1

Table 8-1. Reset and Interrupt Vectors

Vector

No.

1 0x0000 RESET

2 0x0002 ANACOMP 0 Analog Comparator 0 3 0x0004 ANACOMP 1 Analog Comparator 1 4 0x0006 ANACOMP 2 Analog Comparator 2 5 0x0008 ANACOMP 3 Analog Comparator 3 6 0x000A PSC FAULT 7 0x000C PSC EC 8 0x000E INT0 External Interrupt Request 0

9 0x0010 INT1 External Interrupt Request 1 10 0x0012 INT2 External Interrupt Request 2 11 0x0014 INT3 External Interrupt Request 3 12 0x0016 TIMER1 CAPT Timer/Counter1 Capture Event 13 0x0018 TIMER1 COMPA Timer/Counter1 Compare Match A 14 0x001A TIMER1 COMPB Timer/Counter1 Compare Match B 15 0x001C TIMER1 OVF Timer/Counter1 Overflow 16 0x001E TIMER0 COMPA Timer/Counter0 Compare Match A 17 0x0020 TIMER0 COMPB Timer/Counter0 Compare Match B 18 0x0022 TIMER0 OVF Timer/Counter0 Overflow 19 0x0024 CAN INT CAN MOB, Burst, General Errors 20 0x0026 CAN TOVF CAN Timer Overflow 21 0x0028 LIN TC LIN Transfer Complete 22 0x002A LIN ERR LIN Error 23 0x002C PCINT0 Pin Change Interrupt Request 0 24 0x002E PCINT1 Pin Change Interrupt Request 1 25 0x0030 PCINT2 Pin Change Interrupt Request 2 26 0x0032 PCINT3 Pin Change Interrupt Request 3 27 0x0034 SPI, STC SPI Serial Transfer Complete 28 0x0036 ADC ADC Conversion Complete 29 0x0038 WDT Watchdog Time-Out Interrupt 30 0x003A EE READY EEPROM Ready 31 0x003C SPM READY Store Program Memory Ready

Program

Address Source Interrupt Definition

(3)

Atmel ATmega16/32/64/M1/C1

External Pin, Power-on Reset, Brown-out Reset, Watchdog Reset, and Emulation AVR Reset

PSC Fault PSC End of Cycle

7647H–AVR–03/12

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

ATmega16/32/64/M1/C1” on page 279.

2. When the IVSEL bit in MCUCR 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.

3. These vectors are not used by ATmega32/64C1.

Table 8-2 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.

Table 8-2. Reset and Interrupt Vectors Placement in ATmega16/32/64/M1/C1

BOOTRST IVSEL Reset Address Interrupt Vectors Start Address

1 0 0x000 0x001

1 1 0x000 Boot Reset Address + 0x002

0 0 Boot Reset Address 0x001

0 1 Boot Reset Address Boot Reset Address + 0x002

Note: 1. The Boot Reset Address is shown in Table 24-4 on page 283. For the BOOTRST Fuse “1”

means unprogrammed while “0” means programmed.

(1)

The most typical and general program setup for the Reset and Interrupt Vector Addresses in ATmega16/32/64/M1/C1 is:

Address Labels Code Comments 0x000 jmp RESET ; Reset Handler 0x002 jmp ANA_COMP_0 ; Analog Comparator 0 Handler 0x004 jmp ANA_COMP_1 ; Analog Comparator 1 Handler 0x006 jmp ANA_COMP_2 ; Analog Comparator 2 Handler 0x008 jmp ANA_COMP_3 ; Analog Comparator 3 Handler 0x00A jmp PSC_FAULT ; PSC Fault Handler 0x00C jmp PSC_EC ; PSC End of Cycle Handler 0x00E jmp EXT_INT0 ; IRQ0 Handler 0x010 jmp EXT_INT1 ; IRQ1 Handler 0x012 jmp EXT_INT2 ; IRQ2 Handler 0x014 jmp EXT_INT3 ; IRQ3 Handler 0x016 jmp TIM1_CAPT ; Timer1 Capture Handler 0x018 jmp TIM1_COMPA ; Timer1 Compare A Handler 0x01A jmp TIM1_COMPB ; Timer1 Compare B Handler 0x01C jmp TIM1_OVF ; Timer1 Overflow Handler 0x01E jmp TIM0_COMPA ; Timer0 Compare A Handler 0x020 jmp TIM0_COMPB ; Timer0 Compare B Handler 0x022 jmp TIM0_OVF ; Timer0 Overflow Handler 0x024 jmp CAN_INT ; CAN MOB,Burst,General Errors Handler 0x026 jmp CAN_TOVF ; CAN Timer Overflow Handler 0x028 jmp LIN_TC ; LIN Transfer Complete Handler 0x02A jmp LIN_ERR ; LIN Error Handler 0x02C jmp PCINT0 ; Pin Change Int Request 0 Handler

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

Atmel ATmega16/32/64/M1/C1

0x02E jmp PCINT1 ; Pin Change Int Request 1 Handler 0x030 jmp PCINT2 ; Pin Change Int Request 2 Handler 0x032 jmp PCINT3 ; Pin Change Int Request 3 Handler 0x034 jmp SPI_STC ; SPI Transfer Complete Handler 0x036 jmp ADC ; ADC Conversion Complete Handler 0x038 jmp WDT ; Watchdog Timer Handler 0x03A jmp EE_RDY ; EEPROM Ready Handler 0x03C jmp SPM_RDY ; Store Program Memory Ready Handler ; 0x03ERESET: ldi r16, high(RAMEND); Main program start 0x03F out SPH,r16 ; Set Stack Pointer to top of RAM 0x040 ldi r16, low(RAMEND) 0x041 out SPL,r16

0x042 sei ; Enable interrupts 0x043 <instr> xxx

... ... ... ...

When the BOOTRST Fuse is unprogrammed, the Boot section size set to 2K bytes and the IVSEL bit in the MCUCR Register is set before any interrupts are enabled, the most typical and general program setup for the Reset and Interrupt Vector Addresses in ATmega16/32/64/M1/C1 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 0xC02 0xC02 jmp ANA_COMP_0 ; Analog Comparator 0 Handler 0xC04 jmp ANA_COMP_1 ; Analog Comparator 1 Handler

... ... ... ;

0xC3C jmp SPM_RDY ; Store Program Memory Ready Handler

7647H–AVR–03/12

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 in ATmega16/32/64/M1/C1 is:

Address Labels Code Comments .org 0x002 0x002 jmp ANA_COMP_0 ; Analog Comparator 0 Handler 0x004 jmp ANA_COMP_1 ; Analog Comparator 1 Handler

... ... ... ;

0x03C jmp SPM_RDY ; Store Program Memory Ready Handler ; .org 0xC00

0xC00 RESET: ldi r16,high(RAMEND); Main program start 0xC01 out SPH,r16 ; Set Stack Pointer to top of RAM 0xC02 ldi r16,low(RAMEND)

0xC03 out SPL,r16 0xC04 sei ; Enable interrupts

0xC05 <instr> xxx

When the BOOTRST Fuse is programmed, the Boot section size set to 2K bytes and the IVSEL bit in the MCUCR Register is set before any interrupts are enabled, the most typical and general program setup for the Reset and Interrupt Vector Addresses in ATmega16/32/64/M1/C116/32 is:

Address Labels Code Comments ; .org 0xC00

0xC00 jmp RESET ; Reset handler 0xC02 jmp ANA_COMP_0 ; Analog Comparator 0 Handler 0xC04 jmp ANA_COMP_1 ; Analog Comparator 1 Handler

... ... ... ;

0xC3C jmp SPM_RDY ; Store Program Memory Ready Handler ; 0xC3E RESET: ldi r16,high(RAMEND); Main program start 0xC3F out SPH,r16 ; Set Stack Pointer to top of RAM 0xC40 ldi r16,low(RAMEND) 0xC41 out SPL,r16

0xC42 sei ; Enable interrupts 0xC43 <instr> xxx

8.1.1 Moving Interrupts Between Application and Boot Space

The MCU Control Register controls the placement of the Interrupt Vector table.

8.1.2 MCU Control Register – MCUCR

Bit 76543210

SPIPS – – PUD – – IVSEL IVCE MCUCR

Read/Write R/W R R R/W R R R/W R/W Initial Value 0 0 0 0 0 0 0 0

• 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 determined by the BOOTSZ Fuses. Refer to the section “Boot Loader Support – Read-While-Write

Self-Programming ATmega16/32/64/M1/C1” on page 279 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.

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

Atmel ATmega16/32/64/M1/C1

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 ATmega16/32/64/M1/C1” on page 279 for details on Boot

Lock bits.

• 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 Interrupt Vectors

ldi r16, (1<<IVCE) out MCUCR, r16

; Move interrupts to Boot Flash section

ldi r16, (1<<IVSEL) out MCUCR, r16 ret

C Code Example

void Move_interrupts(void) {

/* Enable change of Interrupt Vectors */ MCUCR = (1<<IVCE); /* Move interrupts to Boot Flash section */ MCUCR = (1<<IVSEL);

}

7647H–AVR–03/12

9. I/O-Ports

Logic

See Figure

"General Digital I/O" for

Details

Pxn

9.1 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 changing 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. All port pins have individually selectable pull-up resistors with a supply-voltage invariant resistance. All I/O pins have protection diodes to both V

9-1. Refer to “Electrical Characteristics” on page 317 for a complete list of parameters.

Figure 9-1. I/O Pin Equivalent Schematic

and Ground as indicated in Figure

All registers and bit references in this section are written in general form. A lower case “x” represents 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 Registers and bit locations are listed in “Register Description for I/O-Ports”.

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. However, writing a logic one to a bit in the PINx Register, will result in a toggle in the corresponding bit in the Data Register. In addition, the Pull-up Disable – PUD bit in MCUCR 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”. 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

67. Refer to the individual module sections for a full description of the alternate 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.

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

9.2 Ports as General Digital I/O

clk

RPx

RRx

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

DLQ

RESET

CLR

PORTxn

CLR

DDxn

PINxn

DATA BUS

SLEEP

SLEEP: SLEEP CONTROL

Pxn

I/O

WPx

WRx

WPx: WRITE PINx REGISTER

The ports are bi-directional I/O ports with optional internal pull-ups. Figure 9-2 shows a functional description of one I/O-port pin, here generically called Pxn.

Atmel ATmega16/32/64/M1/C1

Figure 9-2. General Digital I/O

(1)

9.2.1 Configuring the Pin

7647H–AVR–03/12

Note: 1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clk

SLEEP, and PUD are common to all ports.

I/O

Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown in “Register

Description for I/O-Ports” on page 80, 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 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).

9.2.2 Toggling the Pin

Writing a logic one to PINxn toggles the value of PORTxn, independent on the value of DDRxn. Note that the SBI instruction can be used to toggle one single bit in a port.

9.2.3 Switching Between Input and Output

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 acceptable, 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 MCUCR Register can be set to disable all pull-ups in all ports.

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 9-1 summarizes the control signals for the pin value.

Table 9-1. Port Pin Configurations

DDxn PORTxn

PUD

(in MCUCR) I/O Pull-up Comment

0 0 X Input No

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)

9.2.4 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 9-2, the PINxn Register bit and the preceding latch constitute 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 9-3 shows a timing diagram of the synchronization when reading an externally applied pin value. The maximum and minimum propagation delays are denoted t

pd,max

and t

Default configuration after Reset. Tri-state (Hi-Z)

respectively.

pd,min

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

Atmel ATmega16/32/64/M1/C1

XXX in r17, PINx

0x00 0xFF

INSTRUCTIONS

SYNC LATCH

PINxn

r17

XXX

SYSTEM CLK

pd, max

pd, min

out PORTx, r16 nop in r17, PINx

0xFF

0x00 0xFF

SYSTEM CLK

r16

INSTRUCTIONS

SYNC LATCH

PINxn

r17

Figure 9-3. Synchronization when Reading an Externally Applied Pin value

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 indicated by the two arrows t between ½ and 1½ system clock period depending upon the time of assertion.

pd,max

and t

, a single signal transition on the pin will be delayed

pd,min

7647H–AVR–03/12

When reading back a software assigned pin value, a nop instruction must be inserted as indicated in Figure 9-4. The out instruction sets the “SYNC LATCH” signal at the positive edge of the clock. In this case, the delay t

Figure 9-4. Synchronization when Reading a Software Assigned Pin Value

through the synchronizer is 1 system clock period.

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.

Assembly Code Example

...

; Define pull-ups and 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 synchronization

nop

; Read port pins

in r16, PINB ...

(1)

C Code Example

unsigned char i;

...

/* Define pull-ups and set outputs high */ /* Define directions for port pins */ PORTB = (1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0); DDRB = (1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0); /* Insert nop for synchronization*/ _NOP(); /* Read port pins */ i = PINB;

...

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.

9.2.5 Digital Input Enable and Sleep Modes

As shown in Figure 9-2, 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, and Standby mode to avoid high power consumption if some input signals are left floating, or have an analog signal level close to V

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 various other alternate functions as described in “Alternate Port Functions” on page 67.

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.

Atmel ATmega16/32/64/M1/C1

/2.

7647H–AVR–03/12

9.3 Alternate Port Functions

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

DLQ

SET

CLR

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

CLR

PINxn

PORTxn

DDxn

DATA B U S

DIEOVxn

SLEEP

DIEOExn: Pxn DIGITAL INPUT-ENABLE OVERRIDE ENABLE DIEOVxn: Pxn DIGITAL INPUT-ENABLE OVERRIDE VALUE

SLEEP: SLEEP CONTROL

Pxn

I/O

PTOExn

WPx

PTOExn: Pxn, PORT TOGGLE OVERRIDE ENABLE

WPx: WRITE PINx

Most port pins have alternate functions in addition to being general digital I/Os. Figure 9-5 shows how the port pin control signals from the simplified Figure 9-2 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.

Atmel ATmega16/32/64/M1/C1

Figure 9-5. Alternate Port Functions

(1)

7647H–AVR–03/12

Note: 1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clk

SLEEP, and PUD are common to all ports. All other signals are unique for each pin.

Table 9-2 summarizes the function of the overriding signals. The pin and port indexes from Fig- ure 9-5 are not shown in the succeeding tables. The overriding signals are generated internally

in the modules having the alternate function.

I/O

Table 9-2. Generic Description of Overriding Signals for Alternate Functions

Signal Name Full Name Description

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.

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.

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.

If DDOE is set, the Output Driver is enabled/disabled when DDOV is set/cleared, regardless of the setting of the DDxn Register bit.

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.

If PVOE is set, the port value is set to PVOV, regardless of the setting of the PORTxn Register bit.

If PTOE is set, the PORTxn Register bit is inverted.

PUOE

PUOV

DDOE

DDOV

PVOE

PVOV

PTOE

Pull-up Override Enable

Pull-up Override Valu e

Data Direction Override Enable

Data Direction Override Value

Port Value Override Enable

Port Value Override Value

Port Toggle Override Enable

Digital Input

DIEOE

DIEOV

DI Digital Input

AIO

Enable Override Enable

Digital Input Enable Override Valu e

Analog Input/Output

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 mode).

If DIEOE is set, the Digital Input is enabled/disabled when DIEOV is set/cleared, regardless of the MCU state (Normal mode, sleep mode).

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.

This is the Analog Input/output to/from alternate functions. The signal is connected directly to the pad, and can be used bi-directionally.

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.

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

9.3.1 MCU Control Register – MCUCR

Bit 7 6 5 4 3 2 1 0

SPIPS – –PUD– – IVSEL IVCE MCUCR

Read/Write R/W R R R/W R R R/W R/W Initial Value 0 0 0 0 0 0 0 0

• Bit 4 – 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). Se

9.3.2 Alternate Functions of Port B

The Port B pins with alternate functions are shown in Table 9-3.

Table 9-3. Port B Pins Alternate Functions

Port Pin Alternate Functions

PSCOUT0B (PSC output 0B)

PB7

PB6

PB5

PB4

PB3

PB2

ADC4 (Analog Input Channel 4) SCK (SPI Bus Serial Clock) PCINT7 (Pin Change Interrupt 7)

ADC7 (Analog Input Channel 7) PSCOUT1B (PSC output 1B) PCINT6 (Pin Change Interrupt 6)

ADC6 (Analog Input Channel 6) INT2 (External Interrupt 2) ACMPN1 (Analog Comparator 1 Negative Input) AMP2- (Analog Differential Amplicator 2 Negative Input) PCINT5 (Pin Change Interrupt 5)

AMP0+ (Analog Differential Amplifier 0 Positive Input) PCINT4 (Pin Change Interrupt 4)

AMP0- (Analog Differential Amplifier 0 Negative Input) PCINT3 (Pin Change Interrupt 3)

ADC5 (Analog Input Channel5 ) INT1 (External Interrupt 1) ACMPN0 (Analog Comparator 0 Negative Input) PCINT2 (Pin Change Interrupt 2)

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

MOSI (SPI Master Out Slave In)

PB1

PB0

PSCOUT2B (PSC output 2B) PCINT1 (Pin Change Interrupt 1)

MISO (SPI Master In Slave Out) PSCOUT2A (PSC output 2A) PCINT0 (Pin Change Interrupt 0)

The alternate pin configuration is as follows:

• ADC4/PSCOUT0B/SCK/PCINT7 – Bit 7

PSCOUT0B, Output 0B of PSC.

ADC4, Analog to Digital Converter, input channel 4. 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 to be an input, the pull-up can still be controlled by the PORTB7 bit.

PCINT7, Pin Change Interrupt 7.

• ADC7/PSCOUT1B/PCINT6 – Bit 6

ADC7, Analog to Digital Converter, input channel 7 PSCOUT1B, Output 1B of PSC. PCINT6, Pin Change Interrupt 6.

•ADC6/INT2

ADC6, Analog to Digital Converter, input channel 6 INT2, External Interrupt source 2. This pin can serve as an External Interrupt source to the MCU. ACMPN1, Analog Comparator 1 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.

PCINT5, Pin Change Interrupt 5.

• APM0+/PCINT4 – Bit 4

AMP0+, Analog Differential Amplifier 0 Positive Input Channel. PCINT4, Pin Change Interrupt 4.

• AMP0-/PCINT3 – Bit 3

AMP0-, Analog Differential Amplifier 0 Negative Input Channel. 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 Amplifier.

PCINT3, Pin Change Interrupt 3.

•ADC5/INT1

/ACMPN1/AMP2-/PCINT5 – Bit 5

/ACMPN0/PCINT2 – Bit 2

ADC5, Analog to Digital Converter, input channel 5 INT1, External Interrupt source 1. This pin can serve as an external interrupt source to the MCU. ACMPN0, Analog Comparator 0 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.

PCINT2, Pin Change Interrupt 2.

• PCINT1/MOSI/PSCOUT2B – Bit 1

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 DDB1 When the SPI is enabled as a master, the data direction of this pin is controlled by DDB1. When the pin is forced to be an input, the pull-up can still be controlled by the PORTB1 and PUD bits.

PSCOUT2B, Output 2B of PSC. PCINT1, Pin Change Interrupt 1.

• PCINT0/MISO/PSCOUT2A – Bit 0

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

Atmel ATmega16/32/64/M1/C1

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 DDB0. When the SPI is enabled as a slave, the data direction of this pin is controlled by DDB0. When the pin is forced to be an input, the pull-up can still be controlled by the PORTB0 and PUD bits.

PSCOUT2A, Output 2A of PSC. PCINT0, Pin Change Interrupt 0.

Table 9-4 and Table 9-5 relates the alternate functions of Port B to the overriding signals shown

in Figure 9-5 on page 67.

Table 9-4. Overriding Signals for Alternate Functions in PB7..PB4

PB7/ADC4/ PSCOUT0B/SCK/

Signal Name

PUOE SPE • MSTR PUOV PB7 • PUD

DDOE

DDOV PSCen01 1 0 0 PVOE SPE • MSTR • SPIPS

PVOV

DIEOE ADC4D ADC7D ADC6D + In2en AMP0ND DIEOV 0 0 In2en 0 DI SCKin • SPIPS AIO ADC4 ADC7 ADC6 AMP0+

PCINT7

• SPIPS 000

SPE • MSTR + PSCen01

PSCout01 • SPIPS + PSCout01 • PSCen01 • SPIPS

+ PSCout01 • PSCen01 • SPIPS

• SPIPS

• ireset ICP1B INT2

PB6/ADC7/ PSCOUT1B/ PCINT6

PSCen11 0 0

PSCOUT11 0 0

PB5/ADC6/ INT2/ACMPN1/

AMP2-/PCINT5

PB4/AMP0+/ PCINT4

7647H–AVR–03/12

Table 9-5. Overriding Signals for Alternate Functions in PB3..PB0

PB1/MOSI/

PB3/AMP0-/

Signal Name

PUOE00–– PUOV00–– DDOE00–– DDOV00–– PVOE00–– PVOV00–– DIEOE AMP0ND ADC5D + In1en 0 0 DIEOV 0 In1en 0 0

DI INT1

AIO AMP0- ADC5 – –

PCINT3

PB2/ADC5/INT1/ ACMPN0/PCINT2

PSCOUT2B/ PCINT1

MOSI_IN • SPIPS ireset

PB0/MISO/ PSCOUT2A/ PCINT0

•

MISO_IN • SPIPS • ireset

9.3.3 Alternate Functions of Port C

The Port C pins with alternate functions are shown in Table 9-6.

Table 9-6. Port C Pins Alternate Functions

Port Pin Alternate Function

PC7

PC6

PC5

PC4

PC3

D2A (DAC output ) AMP2+ (Analog Differential Amplifier 2 Positive Input) PCINT15 (Pin Change Interrupt 15)

ADC10 (Analog Input Channel 10) ACMP1 (Analog Comparator 1 Positive Input ) PCINT14 (Pin Change Interrupt 14)

ADC9 (Analog Input Channel 9) AMP1+ (Analog Differential Amplifier 1 Input Channel ) ACMP3 (Analog Comparator 3 Positive Input ) PCINT13 (Pin Change Interrupt 13)

ADC8 (Analog Input Channel 8) AMP1- (Analog Differential Amplifier 1 Input Channel ) ACMPN3 (Analog Comparator 3 Negative Input) PCINT12 (Pin Change Interrupt 12)

T1 (Timer 1 clock input) RXCAN (CAN Rx Data) ICP1B (Timer 1 input capture alternate input) PCINT11 (Pin Change Interrupt 11)

T0 (Timer 0 clock input)

PC2

PC1

PC0

Note: On the engineering samples (Parts marked AT90PWM324), the ACMPN3 alternate function is not

located on PC4. It is located on PE2.

TXCAN (CAN Tx Data) PCINT10 (Pin Change Interrupt 10)

PSCIN1 (PSC 1 Digital Input) OC1B (Timer 1 Output Compare B) SS_A (Alternate SPI Slave Select) PCINT9 (Pin Change Interrupt 9)

PSCOUT1A (PSC output 2A) INT3 (External Interrupt 3) PCINT8 (Pin Change Interrupt 8)

The alternate pin configuration is as follows:

• D2A/AMP2+/PCINT15 – Bit 7

D2A, Digital to Analog output AMP2+, Analog Differential Amplifier 2 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 Amplifier.

PCINT15, Pin Change Interrupt 15.

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

Atmel ATmega16/32/64/M1/C1

• ADC10/ACMP1/PCINT14 – Bit 6

ADC10, Analog to Digital Converter, input channel 10. ACMP1, Analog Comparator 1 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.

PCINT14, Pin Change Interrupt 14.

• ADC9/ACMP3/AMP1+/PCINT13 – Bit 5

ADC9, Analog to Digital Converter, input channel 9. ACMP3, Analog Comparator 3 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.

AMP1+, Analog Differential Amplifier 1 Positive Input Channel. 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 Amplifier.

PCINT13, Pin Change Interrupt 13.

• ADC8/AMP1-/ACMPN3/PCINT12 – Bit 4

ADC8, Analog to Digital Converter, input channel 8. AMP1-, Analog Differential Amplifier 1 Negative Input Channel. 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 Amplifier.

ACMPN3, Analog Comparator 3 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.

PCINT12, Pin Change Interrupt 12.

• PCINT11/T1/RXCAN/ICP1B – Bit 3

T1, Timer/Counter1 counter source. RXCAN, CAN Rx Data. ICP1B, Input Capture Pin: The PC3 pin can act as an Input Capture Pin for Timer/Counter1. PCINT11, Pin Change Interrupt 11.

• PCINT10/T0/TXCAN – Bit 2

T0, Timer/Counter0 counter source. TXCAN, CAN Tx Data. PCINT10, Pin Change Interrupt 10.

• PCINT9/PSCIN1/OC1B/SS_A – Bit 1

PCSIN1, PSC 1 Digital Input.

7647H–AVR–03/12

OC1B, Output Compare Match B output: This pin can serve as an external output for the Timer/Counter1 Output Compare B. The pin has to be configured as an output (DDC1 set “one”) to serve this function. This pin is also the output pin for the PWM mode timer function.

SS_A: Slave Port Select input. When the SPI is enabled as a slave, this pin is configured as an input regardless of the setting of DDD0. 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 DDD0. When the pin is forced to be an input, the pull-up can still be controlled by the PORTD0 bit.

PCINT9, Pin Change Interrupt 9.

• PCINT8/PSCOUT1A/INT3

– Bit 0

PSCOUT1A, Output 1A of PSC. INT3, External Interrupt source 3: This pin can serve as an external interrupt source to the MCU. PCINT8, Pin Change Interrupt 8.

Table 9-7 and Table 9-8 relate the alternate functions of Port C to the overriding signals shown

in Figure 9-5 on page 67.

Table 9-7. Overriding Signals for Alternate Functions in PC7..PC4

PC6/ADC10/

PC7/D2A/AMP2+/

Signal Name

PUOE 0 0 0 PUOV 0 0 0 DDOE DAEN 0 0 0 DDOV 0 0 0 0 PVOE 0 0 0 – PVOV 0 0 0 – DIEOE DAEN ADC10D ADC9D ADC8D DIEOV 0 0 0 0 DI

AIO – ADC10 Amp1 ADC9 Amp1+

PCINT15

ACMP1/ PCINT14

PC5/ADC9/ AMP1+/ACMP3/ PCINT13

PC4/ADC8/ AMP1-/ACMPN3/ PCINT12

ADC8 Amp1ACMPN3

Table 9-8. Overriding Signals for Alternate Functions in PC3..PC0

PC3/T1/RXCAN/

Signal Name

PUOE0000 PUOV0000 DDOE 0 PSCen10 DDOV1101 PVOE OC1Ben PSCen10 PVOV OC1B PSCout10 DIEOE In3en DIEOV In3en

DI T1 T0

AIO

ICP1B/PCINT11

PC2/T0/TXCAN/ PCINT10

Atmel ATmega16/32/64/M1/C1

PC1/PSCIN1/ OC1B/SS_A/ PCINT9

PSCin1 SS_A

PC0/INT3/ PSCOUT1A/ PCINT8

INT3

7647H–AVR–03/12

9.3.4 Alternate Functions of Port D

The Port D pins with alternate functions are shown in Table 9-9.

Table 9-9. Port D Pins Alternate Functions

Port Pin Alternate Function

PD7

PD6

PD5

PD4

PD3

Atmel ATmega16/32/64/M1/C1

ACMP0 (Analog Comparator 0 Positive Input ) PCINT23 (Pin Change Interrupt 23)

ADC3 (Analog Input Channel 3 ) ACMPN2 (Analog Comparator 2 Negative Input) INT0 (External Interrupt 0) PCINT22 (Pin Change Interrupt 22)

ADC2 (Analog Input Channel 2) ACMP2 (Analog Comparator 2 Positive Input ) PCINT21 (Pin Change Interrupt 21)

ADC1 (Analog Input Channel 1) RXD/RXLIN (LIN/UART Rx data) ICP1A (Timer 1 input capture) SCK_A (Programming & alternate SPI Clock) PCINT20 (Pin Change Interrupt 20)

TXD/TXLIN (LIN/UART Tx data) OC0A (Timer 0 Output Compare A) SS (SPI Slave Select) MOSI_A (Programming & alternate SPI Master Out Slave In) PCINT19 (Pin Change Interrupt 19)

PSCIN2 (PSC Digital Input 2)

PD2

PD1

PD0

OC1A (Timer 1 Output Compare A) MISO_A (Programming & alternate Master In SPI Slave Out) PCINT18 (Pin Change Interrupt 18)

PSCIN0 (PSC Digital Input 0) CLKO (System Clock Output) PCINT17 (Pin Change Interrupt 17)

PSCOUT0A (PSC output 0A) PCINT16 (Pin Change Interrupt 16)

The alternate pin configuration is as follows:

• ACMP0/PCINT23 – Bit 7

ACMP0, Analog Comparator 0 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.

PCINT23, Pin Change Interrupt 23.

• ADC3/ACMPN2/INT0

/PCINT22 – Bit 6

ADC3, Analog to Digital Converter, input channel 3.

7647H–AVR–03/12

ACMPN2, Analog Comparator 2 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.

INT0, External Interrupt source 0. This pin can serve as an external interrupt source to the MCU. PCINT22, Pin Change Interrupt 23.

• ADC2/ACMP2/PCINT21 – Bit 5

ADC2, Analog to Digital Converter, input channel 2. ACMP2, Analog Comparator 1 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.

PCINT21, Pin Change Interrupt 21.

• PCINT20/ADC1/RXD/RXLIN/ICP1/SCK_A – Bit 4

ADC1, Analog to Digital Converter, input channel 1. RXD/RXLIN, LIN/UART Receive Pin. Receive Data (Data input pin for the LIN/UART). When the

LIN/UART receiver is enabled this pin is configured as an input regardless of the value of DDRD4. When the UART forces this pin to be an input, a logical one in PORTD4 will turn on the internal pull-up.

ICP1, Input Capture Pin1: This pin can act as an input capture pin for Timer/Counter1. SCK_A: 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 DDD4. When the SPI is enabled as a master, the data direction of this pin is controlled by DDD4. When the pin is forced to be an input, the pull-up can still be controlled by the PORTD4 bit.

PCINT20, Pin Change Interrupt 20.

• PCINT19/TXD/TXLIN/OC0A/SS/MOSI_A, Bit 3

TXD/TXLIN, LIN/UART Transmit pin. Data output pin for the LIN/UART. When the LIN/UART Transmitter is enabled, this pin is configured as an output regardless of the value of DDD3.

OC0A, Output Compare Match A output: This pin can serve as an external output for the Timer/Counter0 Output Compare A. The pin has to be configured as an output (DDD3 set “one”) to serve this function. The OC0A pin is also the output pin for the PWM mode

: Slave Port Select input. When the SPI is enabled as a slave, this pin is configured as an input regardless of the setting of DDD3. 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 DDD3. When the pin is forced to be an input, the pull-up can still be controlled by the PORTD3 bit.

MOSI_A: 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 DDD3 When the SPI is enabled as a master, the data direction of this pin is controlled by DDD3. When the pin is forced to be an input, the pull-up can still be controlled by the PORTD3 bit.

PCINT19, Pin Change Interrupt 19.

• PCINT18/PSCIN2/OC1A/MISO_A, Bit 2

PCSIN2, PSC Digital Input 2.

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

Atmel ATmega16/32/64/M1/C1

OC1A, Output Compare Match A output: This pin can serve as an external output for the Timer/Counter1 Output Compare A. The pin has to be configured as an output (DDD2 set “one”) to serve this function. The OC1A pin is also the output pin for the PWM mode timer function.

MISO_A: 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 DDD2. When the SPI is enabled as a slave, the data direction of this pin is controlled by DDD2. When the pin is forced to be an input, the pull-up can still be controlled by the PORTD2 bit.

PCINT18, Pin Change Interrupt 18.

• PCINT17/PSCIN0/CLKO – Bit 1

PCSIN0, PSC Digital Input 0. CLKO, Divided System Clock: The divided system clock can be output on this pin. The divided

system clock will be output if the CKOUT Fuse is programmed, regardless of the PORTD1 and DDD1 settings. It will also be output during reset.

PCINT17, Pin Change Interrupt 17.

• PCINT16/PSCOUT0A – Bit 0

PSCOUT0A: Output 0 of PSC 0. PCINT16, Pin Change Interrupt 16.

Table 9-10 and Table 9-11 relates the alternate functions of Port D to the overriding signals

shown in Figure 9-5 on page 67.

Table 9-10. Overriding Signals for Alternate Functions PD7..PD4

PD7/ ACMP0/

Signal Name

PUOE 0 0 0

PUOV 0 0 0

DDOE 0 0 0

DDOV 0 0 0 0

PVOE 0 0 0

PVOV 0 0 0 –

DIEOE ACMP0D ADC3D + In0en ADC2D ADC1D

DIEOV 0 In0en 0 0

DI – INT0 ICP1A

AIO ACOMP0

PCINT23

PD6/ADC3/ ACMPN2/INT0/ PCINT22

ADC3 ACMPM

PD5/ADC2/ ACMP2/PCINT21

ADC2 ACOMP2

PD4/ADC1/RXD/ RXLIN/ICP1A/ SCK_A/PCINT20

RXEN + SPE •

• SPIPS

MSTR

PD4 • PUD

RXEN + SPE •

• SPIPS

MSTR

SPE • MSTR • SPIPS

ADC1

7647H–AVR–03/12

Table 9-11. Overriding Signals for Alternate Functions in PD3..PD0

PD3/TXD/TXLIN/ OC0A/SS/MOSI_A/

Signal Name

PUOE

PUOV

DDOE

DDOV TXEN 0 0 PSCen00

PVOE

PVOV

DIEOE 0 0 0 0

DIEOV 0 0 0 0

PCINT19

TXEN + SPE • MSTR

• SPIPS

• SPE • MSTR

TXEN

• SPIPS

TXEN + SPE • MSTR

TXEN + OC0en + SPE •

MSTR • SPIPS

TXEN • TXD + TXEN

• (OC0en • OC0 + OC0en • SPIPS • MOSI)

SS MOSI_Ain

• PD3 • PUD

• SPIPS

PD2/PSCIN2/ OC1A/MISO_A/ PCINT18

–0

– 0 PD0 • PUD

–0

– 0 PSCen00 + UMSEL

–0–

PD1/PSCIN0/ CLKO/ PCINT17

PD0/PSCOUT0A/ XCK/PCINT16

SPE • MSTR • SPIPS

PSCen00 + SPE • MSTR • SPIPS

AIO

9.3.5 Alternate Functions of Port E

The Port E pins with alternate functions are shown in Table 9-12.

Table 9-12. Port E Pins Alternate Functions

Port Pin Alternate Function

XTAL2 (XTAL Output)

PE2

PE1

PE0

Note: On the engineering samples (Parts marked AT90PWM324), the ACMPN3 alternate function is not

ADC0 (Analog Input Channel 0) PCINT26 (Pin Change Interrupt 26)

XTAL1 (XTAL Input) OC0B (Timer 0 Output Compare B) PCINT25 (Pin Change Interrupt 25)

RESET# (Reset Input) OCD (On Chip Debug I/O) PCINT24 (Pin Change Interrupt 24)

located on PC4. It is located on PE2.

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

Atmel ATmega16/32/64/M1/C1

The alternate pin configuration is as follows:

• PCINT26/XTAL2/ADC0 – Bit 2

XTAL2: Chip clock Oscillator pin 2. Used as clock pin for crystal Oscillator or Low-frequency crystal Oscillator. When used as a clock pin, the pin can not be used as an I/O pin.

ADC0, Analog to Digital Converter, input channel 0. PCINT26, Pin Change Interrupt 26.

• PCINT25/XTAL1/OC0B – Bit 1

XTAL1: Chip clock Oscillator pin 1. Used for all chip clock sources except internal calibrated RC Oscillator. When used as a clock pin, the pin can not be used as an I/O pin.

OC0B, Output Compare Match B output: This pin can serve as an external output for the Timer/Counter0 Output Compare B. The pin has to be configured as an output (DDE1 set “one”) to serve this function. This pin is also the output pin for the PWM mode timer function.

PCINT25, Pin Change Interrupt 25.

• PCINT24/RESET

/OCD – Bit 0

RESET

, Reset pin: When the RSTDISBL Fuse is programmed, this pin functions as a normal I/O pin, and the part will have to rely on Power-on Reset and Brown-out Reset as its reset sources. When the RSTDISBL Fuse is unprogrammed, the reset circuitry is connected to the pin, and the pin can not be used as an I/O pin.

If PE0 is used as a reset pin, DDE0, PORTE0 and PINE0 will all read 0. PCINT24, Pin Change Interrupt 24.

Table 9-13 relates the alternate functions of Port E to the overriding signals shown in Figure 9-5 on page 67.

Table 9-13. Overriding Signals for Alternate Functions in PE2..PE0

PE2/ADC0/XTAL2/

Signal Name

PUOE000

PUOV000

DDOE 0 0 0

DDOV 0 0 0

PVOE 0 OC0Ben 0

PVOV 0 OC0B 0

DIEOE ADC0D 0 0

DIEOV000

PCINT26

PE1/XTAL1/OC0B/ PCINT25

PE0/RESET OCD/PCINT24

7647H–AVR–03/12

AIO

Osc Output ADC0

Osc / Clock input

9.4 Register Description for I/O-Ports

9.4.1 Port B Data Register – PORTB

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

9.4.2 Port B Data Direction Register – DDRB

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

9.4.3 Port B Input Pins Address – PINB

Bit 76543210

PINB7 PINB6 PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 PINB

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value N/A N/A N/A N/A N/A N/A N/A N/A

9.4.4 Port C Data Register – PORTC

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

9.4.5 Port C Data Direction Register – DDRC

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

9.4.6 Port C Input Pins Address – PINC

Bit 76543210

PINC7 PINC6 PINC5 PINC4 PINC3 PINC2 PINC1 PINC0 PINC

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value N/A N/A N/A N/A N/A N/A N/A N/A

9.4.7 Port D Data Register – PORTD

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

9.4.8 Port D Data Direction Register – DDRD

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

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

9.4.9 Port D Input Pins Address – PIND

Bit 76543210

PIND7 PIND6 PIND5 PIND4 PIND3 PIND2 PIND1 PIND0 PIND

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value N/A N/A N/A N/A N/A N/A N/A N/A

9.4.10 Port E Data Register – PORTE

Bit 76543210

– – – – – PORTE2 PORTE1 PORTE0 PORTE

Read/Write R RRRRR/WR/WR/W Initial Value00000000

9.4.11 Port E Data Direction Register – DDRE

Bit 76543210

– – – – – DDE2 DDE1 DDE0 DDRE

Read/Write R RRRRR/WR/WR/W Initial Value00000000

9.4.12 Port E Input Pins Address – PINE

Bit 76543210

– – – – – PINE2 PINE1 PINE0 PINE

Read/Write R R R R R R/W R/W R/W Initial Value00000N/AN/AN/A

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

10. External Interrupts

clk

pin_lat pin_sync pcint_in[i]

PCINT[i]

PCINT[i] bit

(of PCMSK

)

DQ DQ DQ

clk

pcint_sync pcint_set/flag

PCIF



(interrupt

flag)

PCINT[i] pin

pin_lat

pin_sync

clk

pcint_in[i]

pcint_syn

pcint_set/flag

PCIF

The External Interrupts are triggered by the INT3:0 pins or any of the PCINT23..0 pins. Observe that, if enabled, the interrupts will trigger even if the INT3:0 or PCINT23..0 pins are configured as outputs. This feature provides a way of generating a software interrupt. The pin change interrupt PCI2 will trigger if any enabled PCINT23..16 pin toggles. The pin change interrupt PCI1 will trigger if any enabled PCINT14..8 pin toggles. The pin change interrupt PCI0 will trigger if any enabled PCINT7..0 pin toggles. The PCMSK3, PCMSK2, PCMSK1 and PCMSK0 Registers control which pins contribute to the pin change interrupts. Pin change interrupts on PCINT26..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 INT3:0 interrupts can be triggered by a falling or rising edge or a low level. This is set up as indicated in the specification for the External Interrupt Control Register A – EICRA. When the INT3:0 interrupts are enabled and are configured as level triggered, the interrupts will trigger as long as the pin is held low. Note that recognition of falling or rising edge interrupts on INT3:0 requires the presence of an I/O clock, described in “Clock Systems and their Distribution” on

page 29. Low level interrupt on INT3:0 is detected asynchronously. This implies that this inter-

rupt 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, the required level must be held long enough for the MCU to complete the wake-up to trigger the level interrupt. If the level disappears before the end of the Start-up Time, the MCU will still wake up, but no interrupt will be generated. The start-up time is defined by the SUT and CKSEL Fuses as described in “Clock Systems and their Distribution” on page 29.

10.1 Pin Change Interrupt Timing

An example of timing of a pin change interrupt is schown in Figure 10-1.

Figure 10-1. Timing of a pin change interrupts

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

Atmel ATmega16/32/64/M1/C1

10.2 External Interrupt Control Register A – EICRA

The External Interrupt Control Register A contains control bits for interrupt sense control.

Bit 76543210

ISC31 ISC30 ISC21 ISC20 ISC11 ISC10 ISC01 ISC00 EICRA

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value00000000

• Bit 7..0 – ISC31, ISC30 - ISC01, ISC00: Interrupt Sense Control 0 Bit 1 and Bit 0

The External Interrupts 3 - 0 are activated by the external pins INT3:0 if the SREG I-flag and the corresponding interrupt mask in the EIMSK is set. The level and edges on the external pins that activate the interrupt are defined in Table 10-1. Edges on INT3..INT0 are registered asynchronously. The value on the INT3:0 pins are 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. Observe that CPU clock frequency can be lower than XTAL frequency if the XTAL divider is enabled. If low level interrupt is selected, the low level must be held until the completion of the currently executing instruction to generate an interrupt. If enabled, a level triggered interrupt will generate an interrupt request as long as the pin is held low.

Table 10-1. Interrupt Sense Control

ISCn1 ISCn0 Description

0 0 The low level of INTn generates an interrupt request.

0 1 Any logical change on INTn generates an interrupt request.

Note: 1. n = 3, 2, 1 or 0.

When changing the ISCn1/ISCn0 bits, the interrupt must be disabled by clearing its Interrupt Enable bit in the EIMSK Register. Otherwise an interrupt can occur when the bits are changed.

The falling edge between two samples of INTn generates an interrupt request.

The rising edge between two samples of INTn generates an interrupt request.

10.2.1 External Interrupt Mask Register – EIMSK

Bit 76543210

– – – – INT3 INT2 INT1 INT0 EIMSK

Read/Write RRRRRRR/WR/W Initial Value 0 0 0 0 0 0 0 0

• Bit 7..4 – Res: Reserved Bits

These bits are unused bits in the ATmega16/32/64/M1/C1, and will always read as zero.

• Bit 3..0 – INT3 - 0: External Interrupt Request 3:0 Enable

(1)

7647H–AVR–03/12

When an INT3 – INT0 bit is written to one and the I-bit in the Status Register (SREG) is set (one), the corresponding external pin interrupt is enabled. The Interrupt Sense Control bits in the External Interrupt Control Register A - EICRA defines whether the external interrupt is activated on rising or falling edge or level sensed. Activity on any of these pins will trigger an interrupt request even if the pin is enabled as an output. This provides a way of generating a software interrupt.

10.2.2 External Interrupt Flag Register – EIFR

Bit 76543210

– – – – INTF3 INTF2 INTF1 INTF0 EIFR

Read/Write R R R R R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0

• Bit 7..4 – Res: Reserved Bits

These bits are unused bits in the ATmega16/32/64/M1/C1, and will always read as zero.

• Bit 3..0 – INTF3 - INTF0: External Interrupt Flag 3 - 0

When an edge or logic change on the INT3:0 pin triggers an interrupt request, INTF3:0 becomes set (one). If the I-bit in SREG and the corresponding interrupt enable bit INT3:0 in EIMSK, are set (one), the MCU will jump to the 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. These flags are always cleared when INT3:0 are configured as a level interrupt.

10.2.3 Pin Change Interrupt Control Register - PCICR

Bit 76543210

– – – – PCIE3 PCIE2 PCIE1 PCIE0 PCICR

Read/Write R R R R R R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0

• Bit 7..4 - Res: Reserved Bits

These bits are unused bits in the ATmega16/32/64/M1/C1, and will always read as zero.

• Bit 3 - PCIE3: Pin Change Interrupt Enable 3

When the PCIE3 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin change interrupt 3 is enabled. Any change on any enabled PCINT26..24 pin will cause an interrupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI3 Interrupt Vector. PCINT26..24 pins are enabled individually by the PCMSK3 Register.

• Bit 2 - PCIE2: Pin Change Interrupt Enable 2

When the PCIE2 bit is set (one) and the I-bit in the Status Register (SREG) is set (one), pin change interrupt 2 is enabled. Any change on any enabled PCINT23..16 pin will cause an interrupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI2 Interrupt Vector. PCINT23..16 pins are enabled individually by the PCMSK2 Register.

• Bit 1 - 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 interrupt. 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 0 - 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.

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

10.2.4 Pin Change Interrupt Flag Register - PCIFR

Bit 76543210

– – – – PCIF3 PCIF2 PCIF1 PCIF0 PCIFR

Read/Write R R R R R R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0

• Bit 7..4 - Res: Reserved Bits

These bits are unused bits in the ATmega16/32/64/M1/C1, and will always read as zero.

• Bit 3 - PCIF3: Pin Change Interrupt Flag 3

When a logic change on any PCINT26..24 pin triggers an interrupt request, PCIF3 becomes set (one). If the I-bit in SREG and the PCIE3 bit in PCICR 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.

• Bit 2 - PCIF2: Pin Change Interrupt Flag 2

When a logic change on any PCINT23..16 pin triggers an interrupt request, PCIF2 becomes set (one). If the I-bit in SREG and the PCIE2 bit in PCICR 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.

• Bit 1 - PCIF1: Pin Change Interrupt Flag 1

Atmel ATmega16/32/64/M1/C1

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 PCICR 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.

• Bit 0 - 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 PCICR 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.

10.2.5 Pin Change Mask Register 3 – PCMSK3

Bit 76543210

- - - - - PCINT26 PCINT25 PCINT24 PCMSK3

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

• Bit 7..3 – Res: Reserved Bit

These bits are unused bits in the ATmega16/32/64/M1/C1, and will always read as zero.

• Bit 2..0 – PCINT26..24: Pin Change Enable Mask 26..24

Each PCINT26..24-bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT26..24 is set and the PCIE3 bit in PCICR is set, pin change interrupt is enabled on the corresponding I/O pin. If PCINT23..24 is cleared, pin change interrupt on the corresponding I/O pin is disabled.

7647H–AVR–03/12

10.2.6 Pin Change Mask Register 2 – PCMSK2

Bit 76543210

PCINT23 PCINT22 PCINT21 PCINT20 PCINT19 PCINT18 PCINT17 PCINT16 PCMSK2

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

• Bit 7..0 – PCINT23..16: Pin Change Enable Mask 23..16

Each PCINT23..16-bit selects whether pin change interrupt is enabled on the corresponding I/O pin. If PCINT23..16 is set and the PCIE2 bit in PCICR is set, pin change interrupt is enabled on the corresponding I/O pin. If PCINT23..16 is cleared, pin change interrupt on the corresponding I/O pin is disabled.

10.2.7 Pin Change Mask Register 1 – PCMSK1

Bit 76543210

PCINT15 PCINT14 PCINT13 PCINT12 PCINT11 PCINT10 PCINT9 PCINT8 PCMSK1

Read/Write R R/W R/W R/W R/W R/W R/W R/W Initial Value 0 0 0 0 0 0 0 0

• Bit 7 – Res: Reserved Bit

This bit is an unused bit in the ATmega16/32/64/M1/C1, and will always read as zero.

• 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 PCICR 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.

10.2.8 Pin Change Mask Register 0 – PCMSK0

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 Value 0 0 0 0 0 0 0 0

• 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 PCICR 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.

Atmel ATmega16/32/64/M1/C1

7647H–AVR–03/12

Atmel ATmega16/32/64/M1/C1

Tn_sync

(To Clock Select Logic)

Edge DetectorSynchronization

DQDQ

clk

I/O

11. Timer/Counter0 and Timer/Counter1 Prescalers

Timer/Counter1 and Timer/Counter0 share the same prescaler module, but the Timer/Counters can have different prescaler settings. The description below applies to both Timer/Counter1 and Timer/Counter0.

11.1 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 (f clock source. The prescaled clock has a frequency of either f f

11.2 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/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 artifacts 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).

CLK_I/O

/1024.

). Alternatively, one of four taps from the prescaler can be used as a

CLK_I/O

/8, f

CLK_I/O

/64, f

CLK_I/O

/256, or

It is possible to use the prescaler reset for synchronizing the Timer/Counter to program execution. 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.

11.3 External Clock Source

An external clock source applied to the Tn pin can be used as Timer/Counter clock (clkT1/clkT0). The Tn pin is sampled once every system clock cycle by the pin synchronization logic. The synchronized (sampled) signal is then passed through the edge detector. Figure 11-1 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 ( parent in the high period of the internal system clock.

The edge detector generates one clk (CSn2:0 = 6) edge it detects.

Figure 11-1. Tn Pin Sampling

clk

). The latch is trans-

I/O

/clk

pulse for each positive (CSn2:0 = 7) or negative

7647H–AVR–03/12

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.

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 system clock frequency (f

ExtClk

< f

/2) given a 50/50% duty cycle. Since the edge detector uses

clk_I/O

sampling, the maximum frequency of an external clock it can detect is half the sampling frequency (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 f

clk_I/O

/2.5.

An external clock source can not be prescaled.

Figure 11-2. Prescaler for Timer/Counter0 and Timer/Counter1

clk

I/O

PSRSYNC

Synchronization

Note: 1. The synchronization logic on the input pins (Tn) is shown in Figure 11-1.

11.3.1 General Timer/Counter Control Register – GTCCR

Bit 7 6 543 2 1 0

TSM ICPSEL1

Read/Write R/W R/W R R R R R R/W Initial Value 0 0 0 0 0 0 0 0

– – – – – PSRSYNC GTCCR

clk

Clear

(1)

clk

• 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 PSRSYNC bit 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 configuration. When the TSM bit is written to zero, the PSRSYNC bit is cleared by hardware, and the Timer/Counters start counting simultaneously.

Atmel ATmega16/32/64/M1/C1

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Atmel ATmega16/32/64/M1/C1

• Bit6 – ICPSEL1: Timer 1 Input Capture selection

Timer 1 capture function has two possible inputs ICP1A (PD4) and ICP1B (PC3). The selection is made thanks to ICPSEL1 bit as described in Table 11-1.

Table 11-1. ICPSEL1

ICPSEL1 Description

0 Select ICP1A as trigger for timer 1 input capture

1 Select ICP1B as trigger for timer 1 input capture

• Bit 0 – PSRSYNC: Prescaler Reset

When this bit is one, 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/Counter1 and Timer/Counter0 share the same prescaler and a reset of this prescaler will affect both timers.

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12. 8-bit Timer/Counter0 with PWM

Timer/Counter

DATA BU S

TCNTn

Wavefor m

Generation

OCnA

Control Logic

count clear

direction

TOVn

(Int.Req.)

OCRnx

TCCRnA

Clock Select

Edge

Detector

( From Prescaler )

clk

OCnA

(Int.Req.)

OCRnx

Wavefor m

Generation

OCnB

(Int.Req.)

TCCRnB

Fixed

TOP

Values

TOP BOTTOM

Timer/Counter0 is a general purpose 8-bit Timer/Counter module, with two independent Output Compare Units, and with PWM support. It allows accurate program execution timing (event management) and wave generation. The main features are:

•

Two Independent Output Compare Units

• Double Buffered Output Compare Registers

• Clear Timer on Compare Match (Auto Reload)

• Glitch Free, Phase Correct Pulse Width Modulator (PWM)

• Variable PWM Period

• Frequency Generator

• Three Independent Interrupt Sources (TOV0, OCF0A, and OCF0B)

12.1 Overview

A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 12-1. For the actual placement of I/O pins, refer to “Pin Descriptions” on page 10. 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 locations are listed in the “8-bit Timer/Counter Register Description” on page 101.

The PRTIM0 bit in “Power Reduction Register” on page 42 must be written to zero to enable Timer/Counter0 module.

Figure 12-1. 8-bit Timer/Counter Block Diagram

12.1.1 Definitions

Atmel ATmega16/32/64/M1/C1

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. A lower case “x” replaces the Output Compare Unit, in this case Compare Unit A or Compare Unit B. 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.

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12.1.2 Registers

Atmel ATmega16/32/64/M1/C1

The definitions in Table 12-1 are also used extensively throughout the document. Table 12-1. 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 OCR0A Register. The assignment is dependent on the mode of operation.

The Timer/Counter (TCNT0) and Output Compare Registers (OCR0A and OCR0B) are 8-bit registers. Interrupt request (abbreviated to Int.Req. in the figure) signals are all visible in the Timer Interrupt Flag Register (TIFR0). All interrupts are individually masked with the Timer Interrupt Mask Register (TIMSK0). TIFR0 and TIMSK0 are not shown in the figure.

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 (clk

The double buffered Output Compare Registers (OCR0A and OCR0B) are 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 pins (OC0A and OC0B). See “Using the Output Compare Unit” on page 118. for details. The compare match event will also set the Compare Flag (OCF0A or OCF0B) which can be used to generate an Output Compare interrupt request.

12.2 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 (TCCR0B). For details on clock sources and prescaler, see “Timer/Counter0 and Timer/Counter1 Prescalers” on page 87.

12.3 Counter Unit

The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure

12-2 shows a block diagram of the counter and its surroundings.

Figure 12-2. Counter Unit Block Diagram

DATA BUS

TCNTn Control Logic

count

clear

direction

bottom

top

TOVn

(Int.Req.)

clk

Clock Select

Edge

Detector

( From Prescaler )

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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). clkTn Timer/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 (clk 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 clk count operations.

The counting sequence is determined by the setting of the WGM01 and WGM00 bits located in the Timer/Counter Control Register (TCCR0A) and the WGM02 bit located in the Timer/Counter Control Register B (TCCR0B). There are close connections between how the counter behaves (counts) and how waveforms are generated on the Output Compare outputs OC0A and OC0B. For more details about advanced counting sequences and waveform generation, see “Modes of

Operation” on page 95.

is present or not. A CPU write overrides (has priority over) all counter clear or

). clkT0 can be generated from an external or internal clock source,

The Timer/Counter Overflow Flag (TOV0) is set according to the mode of operation selected by the WGM02:0 bits. TOV0 can be used for generating a CPU interrupt.

12.4 Output Compare Unit

The 8-bit comparator continuously compares TCNT0 with the Output Compare Registers (OCR0A and OCR0B). Whenever TCNT0 equals OCR0A or OCR0B, the comparator signals a match. A match will set the Output Compare Flag (OCF0A or OCF0B) at the next timer clock cycle. If the corresponding interrupt is enabled, the Output Compare Flag generates an Output Compare interrupt. The Output Compare Flag is automatically cleared when the interrupt is executed. Alternatively, the flag can be cleared by software by writing 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 WGM02:0 bits and Compare Output mode (COM0x1:0) 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 (“Modes of Operation” on page 95).

Figure 12-3 shows a block diagram of the Output Compare unit.

Atmel ATmega16/32/64/M1/C1

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Atmel ATmega16/32/64/M1/C1

OCFnx (Int.Req.)

= (8-bit Comparator )

OCRnx

OCnx

DATA BUS

TCNTn

WGMn1:0

Waveform Generator

top

FOCn

COMnx1:0

bottom

Figure 12-3. Output Compare Unit, Block Diagram

The OCR0x Registers are 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 OCR0x Compare Registers 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 OCR0x Register access may seem complex, but this is not case. When the double buffering is enabled, the CPU has access to the OCR0x Buffer Register, and if double buffering is disabled the CPU will access the OCR0x directly.

12.4.1 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 (FOC0x) bit. Forcing compare match will not set the OCF0x Flag or reload/clear the timer, but the OC0x pin will be updated as if a real compare match had occurred (the COM0x1:0 bits settings define whether the OC0x pin is set, cleared or toggled).

12.4.2 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 OCR0x to be initialized to the same value as TCNT0 without triggering an interrupt when the Timer/Counter clock is enabled.

12.4.3 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 Unit, independently of whether the Timer/Counter is running or not. If the value written to TCNT0 equals the OCR0x value, the compare match will be missed, resulting in incorrect waveform generation. Similarly, do not write the TCNT0 value equal to BOTTOM when the counter is downcounting.

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The setup of the OC0x should be performed before setting the Data Direction Register for the port pin to output. The easiest way of setting the OC0x value is to use the Force Output Compare (FOC0x) strobe bits in Normal mode. The OC0x Registers keep their values even when changing between Waveform Generation modes.

Be aware that the COM0x1:0 bits are not double buffered together with the compare value. Changing the COM0x1:0 bits will take effect immediately.

12.5 Compare Match Output Unit

The Compare Output mode (COM0x1:0) bits have two functions. The Waveform Generator uses the COM0x1:0 bits for defining the Output Compare (OC0x) state at the next compare match. Also, the COM0x1:0 bits control the OC0x pin output source. Figure 12-4 shows a simplified schematic of the logic affected by the COM0x1:0 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 COM0x1:0 bits are shown. When referring to the OC0x state, the reference is for the internal OC0x Register, not the OC0x pin. If a system reset occur, the OC0x Register is reset to “0”.

Figure 12-4. Compare Match Output Unit, Schematic

COMnx1 COMnx0

FOCn

clk

I/O

Waveform Generator

OCnx

PORT

DATA BUS

DDR

OCnx

The general I/O port function is overridden by the Output Compare (OC0x) from the Waveform Generator if either of the COM0x1:0 bits are set. However, the OC0x pin direction (input or output) is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction Register bit for the OC0x pin (DDR_OC0x) must be set as output before the OC0x 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 OC0x state before the output is enabled. Note that some COM0x1:0 bit settings are reserved for certain modes of operation. See “8-bit Timer/Counter Register Description” on page 101.

Atmel ATmega16/32/64/M1/C1

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12.5.1 Compare Output Mode and Waveform Generation

The Waveform Generator uses the COM0x1:0 bits differently in Normal, CTC, and PWM modes. For all modes, setting the COM0x1:0 = 0 tells the Waveform Generator that no action on the OC0x Register is to be performed on the next compare match. For compare output actions in the non-PWM modes refer to Table 12-2 on page 101. For fast PWM mode, refer to Table 12-3 on

page 101, and for phase correct PWM refer to Table 12-4 on page 102.

A change of the COM0x1:0 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 FOC0x strobe bits.

12.6 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 (WGM02:0) and Compare Output mode (COM0x1:0) bits. The Compare Output mode bits do not affect the counting sequence, while the Waveform Generation mode bits do. The COM0x1:0 bits control whether the PWM output generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes the COM0x1:0 bits control whether the output should be set, cleared, or toggled at a compare match (See “Compare Match Output Unit” on page 94.).

For detailed timing information refer to “Timer/Counter Timing Diagrams” on page 99.

Atmel ATmega16/32/64/M1/C1

12.6.1 Normal Mode

The simplest mode of operation is the Normal mode (WGM02:0 = 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 bottom (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 Output Compare to generate waveforms in Normal mode is not recommended, since this will occupy too much of the CPU time.

12.6.2 Clear Timer on Compare Match (CTC) Mode

In Clear Timer on Compare or CTC mode (WGM02:0 = 2), the OCR0A Register is used to manipulate the counter resolution. In CTC mode the counter is cleared to zero when the counter value (TCNT0) matches the OCR0A. The OCR0A defines 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 operation of counting external events.

The timing diagram for the CTC mode is shown in Figure 12-5. The counter value (TCNT0) increases until a compare match occurs between TCNT0 and OCR0A, and then counter (TCNT0) is cleared.

7647H–AVR–03/12

Figure 12-5. CTC Mode, Timing Diagram

OCnx

clk_I/O

2 N 1 OCRnx+()⋅⋅

-------------------------------------------------------=

TCNTn

OCnx Interrupt Flag Set

OCn (Toggle)

Period

1 4

2 3

(COMnx1:0 = 1)

An interrupt can be generated each time the counter value reaches the TOP value by using the OCF0A 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 OCR0A is lower than the current value of TCNT0, 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 OC0A output can be set to toggle its logical level on each compare match by setting the Compare Output mode bits to toggle mode (COM0A1:0 = 1). The OC0A 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 f f

/2 when OCR0A is set to zero (0x00). The waveform frequency is defined by the following

clk_I/O

OC0

equation:

The N variable represents the prescale factor (1, 8, 64, 256, or 1024).

12.6.3 Fast PWM Mode

Atmel ATmega16/32/64/M1/C1

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.

The fast Pulse Width Modulation or fast PWM mode (WGM02:0 = 3 or 7) provides a high frequency PWM waveform generation option. The fast PWM differs from the other PWM option by its single-slope operation. The counter counts from BOTTOM to TOP then restarts from BOTTOM. TOP is defined as 0xFF when WGM2:0 = 3, and OCR0A when WGM2:0 = 7. In non-inverting Compare Output mode, the Output Compare (OC0x) is cleared on the compare match between TCNT0 and OCR0x, 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.

7647H–AVR–03/12

Atmel ATmega16/32/64/M1/C1

OCnxPWM

clk_I/O

N 256⋅

---------------------=

In fast PWM mode, the counter is incremented until the counter value matches the TOP value. The counter is then cleared at the following timer clock cycle. The timing diagram for the fast PWM mode is shown in Figure 12-6. The TCNT0 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 TCNT0 slopes represent compare matches between OCR0x and TCNT0.

Figure 12-6. Fast PWM Mode, Timing Diagram

OCRnx Interrupt Flag Set

OCRnx Update and TOVn Interrupt Flag Set

TCNTn

OCn

Period

2 3

4 5 6 7

(COMnx1:0 = 2)

(COMnx1:0 = 3)

The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches TOP. If the interrupt 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 OC0x pins. Setting the COM0x1:0 bits to two will produce a non-inverted PWM and an inverted PWM output can be generated by setting the COM0x1:0 to three: Setting the COM0A1:0 bits to one allows the OC0A pin to toggle on Compare Matches if the WGM02 bit is set. This option is not available for the OC0B pin (see Table 12-6 on page 102). The actual OC0x 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 OC0x Register at the compare match between OCR0x and TCNT0, and clearing (or setting) the OC0x 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 prescale factor (1, 8, 64, 256, or 1024).

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The extreme values for the OCR0A Register represents special cases when generating a PWM waveform output in the fast PWM mode. If the OCR0A is set equal to BOTTOM, the output will be a narrow spike for each MAX+1 timer clock cycle. Setting the OCR0A equal to MAX will result in a constantly high or low output (depending on the polarity of the output set by the COM0A1:0 bits.)

A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting OC0x to toggle its logical level on each compare match (COM0x1:0 = 1). The waveform generated will have a maximum frequency of f feature is similar to the OC0A toggle in CTC mode, except the double buffer feature of the Output Compare unit is enabled in the fast PWM mode.

12.6.4 Phase Correct PWM Mode

The phase correct PWM mode (WGM02:0 = 1 or 5) 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 TOP and then from TOP to BOTTOM. TOP is defined as 0xFF when WGM2:0 = 1, and OCR0A when WGM2:0 = 5. In non-inverting Compare Output mode, the Output Compare (OC0x) is cleared on the compare match between TCNT0 and OCR0x while upcounting, and set on the compare match while downcounting. 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.

In phase correct PWM mode the counter is incremented until the counter value matches TOP. When the counter reaches TOP, it changes the count direction. The TCNT0 value will be equal to TOP for one timer clock cycle. The timing diagram for the phase correct PWM mode is shown on Figure 12-7. 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 OCR0x and TCNT0.

OC0

= f

/2 when OCR0A is set to zero. This

clk_I/O

Figure 12-7. Phase Correct PWM Mode, Timing Diagram

OCnx Interrupt Flag Set

OCRnx Update

TOVn Interrupt Flag Set

TCNTn

OCnx

Period

1 2 3

(COMnx1:0 = 2)

(COMnx1:0 = 3)

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.

Atmel ATmega16/32/64/M1/C1

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Atmel ATmega16/32/64/M1/C1

OCnxPCPWM

clk_I/O

N 510⋅

---------------------=

clk

(clk

I/O

/1)

TOVn

clk

I/O

TCNTn MAX - 1 MAX BOTTOM BOTTOM + 1

In phase correct PWM mode, the compare unit allows generation of PWM waveforms on the OC0x pins. Setting the COM0x1:0 bits to two will produce a non-inverted PWM. An inverted PWM output can be generated by setting the COM0x1:0 to three: Setting the COM0A0 bits to one allows the OC0A pin to toggle on Compare Matches if the WGM02 bit is set. This option is not available for the OC0B pin (see Table 12-7 on page 103). The actual OC0x 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 OC0x Register at the compare match between OCR0x and TCNT0 when the counter increments, and setting (or clearing) the OC0x Register at compare match between OCR0x and TCNT0 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 prescale factor (1, 8, 64, 256, or 1024).

The extreme values for the OCR0A Register represent special cases when generating a PWM waveform output in the phase correct PWM mode. If the OCR0A is set equal to BOTTOM, the output 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 12-7 OCnx 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.

• OCRnx changes its value from MAX, like in Figure 12-7. When the OCR0A 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 OCnx 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 OCRnx, and for that reason misses the Compare Match and hence the OCnx change that would have happened on the way up.

12.7 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 12-8 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 12-8. Timer/Counter Timing Diagram, no Prescaling

7647H–AVR–03/12

Figure 12-9 shows the same timing data, but with the prescaler enabled.

TOVn

TCNTn

MAX - 1 MAX BOTTOM BOTTOM + 1

clk

I/O

clk

(clk

I/O

/8)

OCFnx

OCRnx

TCNTn

OCRnx Value

OCRnx - 1 OCRnx OCRnx + 1 OCRnx + 2

clk

I/O

clk

(clk

I/O

/8)

OCFnx

OCRnx

TCNTn

(CTC)

TOP

TOP - 1 TOP BOTTOM BOTTOM + 1

clk

I/O

clk

(clk

I/O

/8)

Figure 12-9. Timer/Counter Timing Diagram, with Prescaler (f

clk_I/O

/8)

Figure 12-10 shows the setting of OCF0B in all modes and OCF0A in all modes except CTC

mode and PWM mode, where OCR0A is TOP.

Figure 12-10. Timer/Counter Timing Diagram, Setting of OCF0x, with Prescaler (f

clk_I/O

/8)

Figure 12-11 shows the setting of OCF0A and the clearing of TCNT0 in CTC mode and fast

PWM mode where OCR0A is TOP.

Figure 12-11. Timer/Counter Timing Diagram, Clear Timer on Compare Match mode, with Pres-

caler (f

100

Atmel ATmega16/32/64/M1/C1

clk_I/O

/8)

7647H–AVR–03/12

Atmel ATmega32M1, ATmega64C1, ATmega16M1, ATmega32C1, ATmega64M1 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Features

1. Pin Configurations

1.1 Pin Descriptions

2. Overview

2.1 Block Diagram

2.2 Automotive Quality Grade

2.3 Pin Descriptions

2.3.1 VCC

2.3.2 GND

2.3.3 Port B (PB7..PB0)

2.3.4 Port C (PC7..PC0)

2.3.5 Port D (PD7..PD0)

2.3.7 AVCC

2.3.8 AREF

2.4 About Code Examples

3. AVR CPU Core

3.1 Introduction

3.2 Architectural Overview

3.3 ALU – Arithmetic Logic Unit

3.4 Status Register

3.5 General Purpose Register File

3.5.1 The X-register, Y-register, and Z-register

3.6 Stack Pointer

3.7 Instruction Execution Timing

3.8 Reset and Interrupt Handling

3.8.1 Interrupt Behavior

3.8.2 Interrupt Response Time

4. Memories

4.1 In-System Reprogrammable Flash Program Memory

4.2 SRAM Data Memory

4.2.1 SRAM Data Access Times

4.3 EEPROM Data Memory

4.3.1 EEPROM Read/Write Access

4.3.2 The EEPROM Address Registers – EEARH and EEARL

4.3.3 The EEPROM Data Register – EEDR

4.3.4 The EEPROM Control Register – EECR

4.3.5 Preventing EEPROM Corruption

4.4 I/O Memory

4.5 General Purpose I/O Registers

4.5.1 General Purpose I/O Register 0 – GPIOR0

4.5.2 General Purpose I/O Register 1 – GPIOR1

4.5.3 General Purpose I/O Register 2 – GPIOR2

5. System Clock

5.1 Clock Systems and their Distribution

5.2 Clock Sources

5.3 Default Clock Source

5.4 Low Power Crystal Oscillator

5.5 Calibrated Internal RC Oscillator

5.5.1 Oscillator Calibration Register – OSCCAL

5.6 PLL

5.6.1 Internal PLL

5.6.2 PLL Control and Status Register – PLLCSR

5.7 128 kHz Internal Oscillator

5.8 External Clock

5.9 Clock Output Buffer

5.10 System Clock Prescaler

5.10.1 Clock Prescaler Register – CLKPR

6. Power Management and Sleep Modes

6.1 Sleep Mode Control Register

6.1.1 Sleep Mode Control Register – SMCR

6.2 Idle Mode

6.3 ADC Noise Reduction Mode

6.4 Power-down Mode

6.5 Standby Mode

6.6 Power Reduction Register

6.6.1 Power Reduction Register - PRR

6.7 Minimizing Power Consumption

6.7.1 Analog to Digital Converter

6.7.2 Analog Comparator

6.7.3 Brown-out Detector

6.7.4 Internal Voltage Reference

6.7.5 Watchdog Timer

6.7.6 Port Pins

6.7.7 On-chip Debug System

7. System Control and Reset

7.1 Resetting the AVR