Rainbow Electronics ATmega128L User Manual

Features

• High-performance, Low-power AVR

• Advanced RISC Architecture

– 133 Powerful Instructions – Most Single Clock Cycle Execution – 32 x 8 General Purpose Working Registers + Peripheral Control Registers – Fully Static Operation – Up to 16 MIPS Throughput at 16 MHz – On-chip 2-cycle Multiplier

• Nonvolatile Program and Data Memories

– 128K Bytes of In-System Reprogrammable Flash

Endurance: 1,000 Write/Erase Cycles

– Optional Boot Code Section with Independent Lock Bits

In-System Programming by On-chip Boot Program True Read-While-Write Operation

– 4K Bytes EEPROM

Endurance: 100,000 Write/Erase Cycles – 4K Bytes Internal SRAM – Up to 64K Bytes Optional External Memory Space – Programming Lock for Software Security – SPI Interface for In-System Programming

• JTAG (IEEE std. 1149.1 Compliant) Interface

– Boundary-scan Capabilities According to the JTAG Standard – Extensive On-chip Debug Support – Programming of Flash, EEPROM, Fuses and Lock Bits through the JTAG Interface

• Peripheral Features

– Two 8-bit Timer/Counters with Separate Prescalers and Compare Modes – Two Expanded 16-bit Timer/Counters with Separate Prescaler, Compare Mode and

Capture Mode – Real Time Counter with Separate Oscillator – Two 8-bit PWM Channels – 6 PWM Channels with Programmable Resolution from 1 to 16 Bits – 8-channel, 10-bit ADC

8 Single-ended Channels 7 Differential Channels

2 Differential Channels with Programmable Gain at 1x, 10x, or 200x – Byte-oriented 2-wire Serial Interface – Dual Programmable Serial USARTs – Master/Slave SPI Serial Interface – Programmable Watchdog Timer with On-chip Oscillator – On-chip Analog Comparator

• Special Microcontroller Features

– Power-on Reset and Programmable Brown-out Detection – Internal Calibrated RC Oscillator – External and Internal Interrupt Sources – Six Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down, Standby

and Extended Standby – Software Selectable Clock Frequency – ATmega103 Compatibility Mode Selected by a Fuse – Global Pull-up Disable

• I/O and Packages

– 53 Programmable I/O Lines – 64-lead TQFP

• Operating Voltages

– 2.7 - 5.5V for ATmega128L – 4.5 - 5.5V for ATmega128

• Speed Grades

– 0 - 8 MHz for ATmega128L – 0 - 16 MHz for ATmega128

8-bit Microcontroller

8-bit Microcontroller with 128K Bytes In-System Programmable Flash

ATmega128 ATmega128L

Preliminary

Rev. 2467B-09/01

Pin Configurations Figure 1. Pinout ATmega128

AVCC

GND

AREF

PF0 (ADC0)

PF1 (ADC1)

PF2 (ADC2)

PF3 (ADC3)

PF4 (ADC4/TCK)

PF5 (ADC5/TMS)

PF6 (ADC6/TDO)

PF7 (ADC7/TDI)

GND

VCC

PA0 (AD0)

PA1 (AD1)

PA2 (AD2)

PEN

RXD0/(PDI) PE0

(TXD0/PDO) PE1

(XCK0/AIN0) PE2 (OC3A/AIN1) PE3 (OC3B/INT4) PE4

(OC3C/INT5) PE5

(T3/INT6) PE6

(IC3/INT7) PE7

(SS) PB0

(SCK) PB1 (MOSI) PB2 (MISO) PB3

(OC0) PB4

(OC1A) PB5 (OC1B) PB6

646362616059585756555453525150

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

171819202122232425262728293031

VCC

GND

XTAL2

RESET

TOSC2/PG3

TOSC1/1PG4

(OC2/OC1C) PB7

XTAL1

(SCL/INT0) PD0

(SDA/INT1) PD1

(RXD1/INT2) PD2

(TXD1/INT3) PD3

(T1) PD6

(IC1) PD4

(XCK1) PD5

49 48

PA3 (AD3)

PA4 (AD4)

PA5 (AD5)

PA6 (AD6)

PA7 (AD7)

PG2(ALE)

PC7 (A15)

PC6 (A14)

PC5 (A13)

PC4 (A12)

PC3 (A11)

PC2 (A10)

PC1 (A9)

PC0 (A8)

PG1(RD)

PG0(WR)

(T2) PD7

Overview The ATmega128 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 ATmega128 achieves throughputs approaching 1 MIPS per MHz allowing the system designer to optimize power consumption versus processing speed.

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Block Diagram

Figure 2. Block Diagram

ATmega128(L)

VCC

GND

AVCC

AGND

AREF

PEN

DATA REGISTER

JTAG TAP

ON-CHIP DEBUG

BOUNDARY-

SCAN

PROGRAMMING

LOGIC

PORTF DRIVERS

PORTF

DATA DIR.

REG. PORTF

ADC

PROGRAM COUNTER

PROGRAM

FLASH

INSTRUCTION

DECODER

DATA REGISTER

PORTA

STACK

POINTER

SRAM

GENERAL PURPOSE

REGISTERS

PA0 - PA7PF0 - PF7

PORTA DRIVERS

DATA DIR.

REG. PORTA

8-BIT DATA BUS

INTERNAL

OSCILLATOR

WATCHDOG

TIMER

MCU CONTROL

TIMER/

COUNTERS

INTERRUPT

UNIT

PORTC DRIVERS

DATA REGISTER

PORTC

CALIB. OSC

OSCILLATOR

TIMING AND

CONTROL

PC0 - PC7

DATA DIR.

REG. PORTC

XTAL1

XTAL2

RESET

TOR

ANALOG

COMPARA

DATA REGISTER

USART0

PORTE

CONTROL

LINES

DATA DIR.

REG. PORTE

PORTE DRIVERS

ALU

STATUS

DATA REGISTER

PORTB

PORTB DRIVERS

PB0 - PB7PE0 - PE7

DATA DIR.

REG. PORTB

EEPROM

SPI

DATA REGISTER

PORTD

PORTD DRIVERS

PD0 - PD7

USART1

DATA DIR.

REG. PORTD

2-WIRE SERIAL

INTERFACE

DATA REG.

PORTG

DATA DIR.

REG. PORTG

PORTG DRIVERS

PG0 - PG4

2467B–09/01

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.

The ATmega128 provides the following features: 128K bytes of In-System Programmable Flash with Read-While-Write capabilities, 4K bytes EEPROM, 4K bytes SRAM, 53 general-purpose I/O lines, 32 general purpose working registers, Real Time Counter (RTC), four flexible timer/counters with compare modes and PWM, 2 USARTs, a byte oriented 2-wire Serial Interface, an 8-channel, 10-bit ADC with optional differential input stage with programmable gain, programmable Watchdog Timer with internal oscillator, an SPI serial port, IEEE std. 1149.1 compliant JTAG test interface, also used for accessing the On-chip Debug system and programming and six software selectable power saving modes. The Idle mode stops the CPU while allowing the SRAM, timer/counters, SPI port, and interrupt system to continue functioning. The Power-down mode saves the register contents but freezes the oscillator, disabling all other chip functions until the next interrupt or hardware reset. In Power-save mode, the asynchronous timer continues to run, allowing the user to maintain a timer base while the rest of the device is sleeping. The ADC Noise Reduction Mode stops the CPU and all I/O modules except asynchronous timer and 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. In Extended Standby mode, both the main oscillator and the asynchronous timer continue to run.

ATmega103 and ATmega128 Compatibility

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 ATmega128 is a powerful microcontroller that provides a highly flexible and cost effective solution to many embedded control applications.

The ATmega128 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.

The ATmega128 is a highly complex microcontroller where the number of I/O locations supersedes the 64 I/O location reserved in the AVR instruction set. To ensure backward compatibility with the ATmega103, all I/O locations present in ATmega103 have the same location in ATmega128. Most additional I/O locations are added in an Extended I/O space starting from $60 to $FF, (i.e., in the ATmega103 internal RAM space). These location can be reached by using LD/LDS/LDD and ST/STS/STD instruction only, not by using IN and OUT instruction. The relocation of the internal RAM space may still be a problem for ATmega103 users. Also, the increased number of interrupt vectors might be a problem if the code uses absolute addresses. To solve these problems, an ATmega103 compatibility mode can be selected by programming the fuse M103C. In this mode, none of the functions in the Extended I/O space are in use, so the internal RAM is located as in ATmega103. Also, the extended interrupt vectors are removed.

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ATmega128(L)

The ATmega128 is 100% pin compatible with ATmega103, and can replace the ATmega103 on current Printed Circuit Boards. The application note “Replacing ATmega103 by ATmega128” describes what the user should be aware of replacing the ATmega103 by an ATmega128.

ATmega103 Compatibility Mode

By programming the M103C fuse, the ATmega128 will be compatible with the ATmega103 regards to RAM, I/O pins and interrupt vectors as described above. However, some new features in ATmega128 are not available in this compatibility mode, these features are listed below:

• One USART instead of two, asynchronous mode only. Only the 8 least significant bits of the Baud Rate Register is available.

• One 16 bits Timer/Counter with 2 compare registers instead of two 16-bit Timer/Counters with 3 compare registers.

• 2-wire serial interface is not supported.

• Port G serves alternate functions only (not a general I/O port).

• Port F serves as digital input only in addition to analog input to the ADC.

• Boot Loader capabilities is not supported.

• It is not possible to adjust the frequency of the internal calibrated RC oscillator.

• The External Memory Interface can not release any Address pins for general I/O,

neither configure different wait-states to different External Memory Address sections.

Pin Descriptions

VCC Digital supply voltage.

GND Ground.

Port A (PA7..PA0) Port A is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each

bit). The Port A output buffers have symmetrical drive characteristics with both high sink and source capability. As inputs, Port A pins that are externally pulled low will source current if the pull-up resistors are activated. The Port A pins are tri-stated when a reset condition becomes active, even if the clock is not running.

Port A also serves the functions of various special features of the ATmega128 as listed

page 68.

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 ATmega128 as listed

page 69.

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.

2467B–09/01

Port C also serves the functions of special features of the ATmega128 as listed on page

. In ATmega103 compatibility mode, Port C is output only, and the port C pins are not

tri-stated when a reset condition becomes active.

Port D (PD7..PD0) Port D is an 8-bit bidirectional 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 ATmega128 as listed

page 73.

Port E (PE7..PE0) Port E is an 8-bit bidirectional I/O port with internal pull-up resistors (selected for each

bit). The Port E output buffers have symmetrical drive characteristics with both high sink and source capability. As inputs, Port E pins that are externally pulled low will source current if the pull-up resistors are activated. The Port E pins are tri-stated when a reset condition becomes active, even if the clock is not running.

Port E also serves the functions of various special features of the ATmega128 as listed

page 76.

Port F (PF7..PF0) Port F serves as the analog inputs to the A/D Converter.

Port F also serves as an 8-bit bi-directional I/O port, if the A/D Converter is not used. Port pins can provide internal pull-up resistors (selected for each bit). The Port F output buffers have symmetrical drive characteristics with both high sink and source capability. As inputs, Port F pins that are externally pulled low will source current if the pull-up resistors are activated. The Port F pins are tri-stated when a reset condition becomes active, even if the clock is not running. If the JTAG interface is enabled, the pull-up resistors on pins PF7(TDI), PF5(TMS) and PF4(TCK) will be activated even if a reset occurs.

Port F also serves the functions of the JTAG interface.

In ATmega103 compatibility mode, Port F is an input Port only.

Port G (PG4..PG0) Port G is a 5-bit bidirectional I/O port with internal pull-up resistors (selected for each

bit). The Port G output buffers have symmetrical drive characteristics with both high sink and source capability. As inputs, Port G pins that are externally pulled low will source current if the pull-up resistors are activated. The Port G pins are tri-stated when a reset condition becomes active, even if the clock is not running.

Port G also serves the functions of various special features.

The port G pins are tri-stated when a reset condition becomes active, even if the clock is not running.

In ATmega103 compatibility mode, these pins only serves as strobes signals to the external memory as well as input to the 32 kHz oscillator, and the pins are initialized to PG0 = 1, PG1 = 1, and PG2 = 0 asynchronously when a reset condition becomes active, even if the clock is not running. PG3 and PG4 are oscillator pins.

RESET

XTAL1 Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

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

19 on page 46

. Shorter pulses are not guaranteed to generate a reset.

Table

ATmega128(L)

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ATmega128(L)

XTAL2 Output from the inverting oscillator amplifier.

AVCC This is the supply voltage pin for Port F and the A/D Converter. It should be externally

connected to VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC through a low-pass filter.

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

PEN This is a programming enable pin for the serial programming mode. By holding this pin

low during a power-on reset, the device will enter the serial programming mode. PEN has no function during normal operation.

About Code Examples

This datasheet 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.

2467B–09/01

AVR CPU Core

Introduction This chapter discusses the AVR core architecture in general. The main function of the

CPU core is to ensure correct program execution. The CPU must therefore be able to access memories, perform calculations, control peripherals and handle interrupts.

Architectural Overview Figure 3. Block Diagram of the AVR Architecture

Data Bus 8-bit

Flash

Program

Memory

Instruction

Decoder

Control Lines

Program

Counter

Direct Addressing

Indirect Addressing

Status

and Control

32 x 8 General Purpose

Registrers

ALU

Data

SRAM

EEPROM

I/O Lines

Interrupt

Unit

SPI

Unit

Watchdog

Timer

Analog

Comparator

I/O Module1

I/O Module 2

I/O Module n

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.

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-register, Y-register 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

ATmega128(L)

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ATmega128(L)

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 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 the priority.

The I/O memory space contains 64 addresses which can be accessed directly, or as the Data Space locations following those of the Register file, $20 - $5F. In addition, the ATmega128 has Extended I/O space from $60 - $FF in SRAM where only the ST/STS/STD and LD/LDS/LDD instructions can be used.

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 “Instruc- tion Set” section for a detailed description.

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 value00000000

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• Bit 7 - I: Global Interrupt Enable

The global interrupt enable bit must be set for the interrupts to be enabled. The individual 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 Ibit can also be set and cleared in software 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

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

⊕ V

General Purpose Register File

The negative flag N indicates a negative result in an arithmetic or logic operation. See the “Instruction Set Description” for detailed information.

• Bit 1 - Z: Zero Flag

The zero flag Z indicates a zero result in an arithmetic or logic operation. See the “Instruction Set Description” for detailed information.

• Bit 0 - C: Carry Flag

The carry flag C indicates a carry in an arithmetic or logic operation. See the “Instruction Set Description” for detailed information.

The Register file is optimized for the AVR Enhanced RISC instruction set. In order to achieve the required performance and flexibility, the following input/output schemes are supported by the Register file:

• One 8-bit output operand and one 8-bit result input

• Two 8-bit output operands and one 8-bit result input

• Two 8-bit output operands and one 16-bit result input

• One 16-bit output operand and one 16-bit result input

Figure 4 shows the structure of the 32 general purpose working registers in the CPU.

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ATmega128(L)

Figure 4. AVR CPU General Purpose Working Registers

7 0 Addr.

R0 $00

R1 $01

R2 $02

…

R13 $0D

General R14 $0E

Purpose R15 $0F

Working R16 $10

Registers R17 $11

…

R26 $1A X-register low byte

R27 $1B X-register high byte

R28 $1C Y-register low byte

R29 $1D Y-register high byte

R30 $1E Z-register low byte

R31 $1F 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.

X-register, Y-register and Zregister

As shown in

Figure 4, each register is also assigned a data memory address, mapping

them directly into the first 32 locations of the user Data Space. Although not being physically 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.

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 described in

Figure 5.

Figure 5. The X, Y and Z Registers

15 XH XL 0

X - register 7 0 7 0

R27 ($1B) R26 ($1A)

15 YH YL 0

Y - register 7 0 7 0

R29 ($1D) R28 ($1C)

15 ZH ZL 0

Z - register 7 0 7 0

R31 ($1F) R30 ($1E)

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In the different addressing modes these address registers have functions as fixed displacement, automatic increment, and automatic decrement (see the Instruction Set Reference for details).

Stack Pointer The stack is mainly used for storing temporary data, for storing local variables and for

storing return addresses after interrupts and subroutine calls. The stack pointer register always points to the top of the stack. Note that the stack is implemented as growing from higher memory 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 $60. 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 151413121110 9 8

SP15 SP14 SP13 SP12 SP11 SP10 SP9 SP8 SPH

SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 SPL

76543210

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

R/W R/W R/W R/W R/W R/W R/W R/W

Initial value00000000

00000000

RAM Page Z Select Register – RAMPZ

Bit 7 6 5 4 3 2 1 0

– –– – – – – – RAMPZ0 RAMPZ

Read/Write R R R R R R R R/W

Initial value 0 0 0 0 0 0 0 0

• Bits 7..2 - Res: Reserved Bits

These are reserved bits and will always read as zero. When writing to this address location, write these bits to zero for compatibility with future devices.

• Bit 1 - RAMPZ0: Extended RAM Page Z-pointer

The RAMPZ register is normally used to select which 64K RAM Page is accessed by the Z pointer. As the ATmega128 does not support more than 64K of SRAM memory, this register is used only to select which page in the program memory is accessed when the ELPM/SPM instruction is used. The different settings of the RAMPZ0 bit have the following effects:

RAMPZ0 = 0: Program memory address $0000- $7FFF (lower 64K bytes) is

accessed by ELPM/SPM

RAMPZ0 = 1: Program memory address $8000- $FFFF (higher 64K bytes) is

accessed by ELPM/SPM

Note that LPM is not affected by the RAMPZ setting.

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ATmega128(L)

Instruction Execution Timing

This section describes the general access timing concepts for instruction execution. The AVR CPU is driven by the CPU clock clk

, directly generated from the selected clock

CPU

source for the chip. No internal clock division is used.

Figure 6 shows the parallel instruction fetches and instruction executions enabled by the

Harvard architecture and the fast-access Register file concept. This is the basic pipelining concept to obtain up to 1 MIPS per MHz with the corresponding unique results for functions per cost, functions per clocks, and functions per power-unit.

Figure 6. The Parallel Instruction Fetches and Instruction Executions

T1 T2 T3 T4

clk

CPU

1st Instruction Fetch

1st Instruction Execute

2nd Instruction Fetch

2nd Instruction Execute

3rd Instruction Fetch

3rd Instruction Execute

4th Instruction Fetch

Figure 7 shows the internal timing concept for the Register file. In a single clock cycle an

ALU operation using two register operands is executed, and the result is stored back to the destination register.

Figure 7. Single Cycle ALU Operation

T1 T2 T3 T4

Reset and Interrupt Handling

clk

Total Execution Time

ALU Operation Execute

Result Write Back

CPU

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 Programming” on page 279 for details.

The lowest addresses in the program memory space are by default defined as the Reset and Interrupt vectors. The complete list of vectors is shown in

“Interrupts” on page 54.

The list also determines the priority levels of the different interrupts. The lower the address the higher is the priority level. RESET has the highest priority, and next is INT0 – the External Interrupt Request 0. The interrupt vectors can be moved to the start of the boot Flash section by setting the IVSEL bit in the MCU Control Register (MCUCR). Refer to

“Interrupts” on page 54 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” on page 266.

2467B–09/01

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.

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.

ATmega128(L)

2467B–09/01

ATmega128(L)

Assembly Code Example

sei ; set global interrupt enable

sleep ; enter sleep, waiting for interrupt

; note: will enter sleep before any pending

; interrupt(s)

C Code Example

_SEI(); /* set global interrupt enable */

_SLEEP(); /* enter sleep, waiting for interrupt */

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

Interrupt Response Time The interrupt execution response for all the enabled AVR interrupts is 4 clock cycles

minimum. After 4 clock cycles, the program vector address for the actual interrupt handling routine is executed. During this 4-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 3 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 4 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 4 clock cycles. During these 4-clock cycles, the Program Counter (2 bytes) is popped back from the Stack, the Stack Pointer is incremented by 2, and the I-bit in SREG is set.

2467B–09/01

AVR ATmega128 Memories

This section describes the different memories in the ATmega128. The AVR architecture has two main memory spaces, the Data Memory and the Program Memory space. In addition, the ATmega128 features an EEPROM Memory for data storage. All three memory spaces are linear and regular.

In-System Reprogrammable Flash Program Memory

The ATmega128 contains 128K 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 64K 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 1,000 write/erase cycles. The ATmega128 Program Counter (PC) is 16 bits wide, thus addressing the 64K program memory locations. The operation of Boot Program section and associated Boot Lock Bits for software protection are described in detail in

While-Write Self-Programming” on page 266

tains a detailed description on Flash data serial downloading using the SPI pins or the JTAG interface.

Constant tables can be allocated within the entire program memory address space (see the LPM – Load Program Memory and ELPM – Extended Load Program Memory instruction description).

Timing diagrams for instruction fetch and execution are presented in

tion Timing” on page 13

Figure 8. Program Memory Map

Program Memory

. “Memory Programming” on page 279 con-

“Boot Loader Support – Read-

“Instruction Execu-

$0000

Application Flash Section

Boot Flash Section

$FFFF

ATmega128(L)

2467B–09/01

ATmega128(L)

SRAM Data Memory The ATmega128 supports two different configurations for the SRAM data memory as

listed in

Table 1. Memory Configurations

Configuration Internal SRAM Data Memory External SRAM Data Memory

Normal Mode 4096 up to 64K

Table 1.

ATmega103 Compatibility Mode

Figure 9 shows how the ATmega128 SRAM Memory is organized.

The ATmega128 is a complex microcontroller with more peripheral units than can be supported within the 64 location reserved in the Opcode for the IN and OUT instructions. For the Extended I/O space from $60 - $FF in SRAM, only the ST/STS/STD and LD/LDS/LDD instructions can be used. The Extended I/O space does not exist when the ATmega128 is in the ATmega103 compatibility mode.

In normal mode, the first 4352 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 4096 locations address the internal data SRAM.

In ATmega103 compatibility mode, the first 4096 Data Memory locations address both the Register file, the 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, and the next 4000 locations address the internal data SRAM.

An optional external data SRAM can be used with the ATmega128. This SRAM will occupy an area in the remaining address locations in the 64K address space. This area starts at the address following the internal SRAM. The Register file, I/O, Extended I/O and Internal SRAM uses the occupies the lowest 4352 bytes in normal mode, and the lowest 4096 bytes in the ATmega103 compatibility mode (Extended I/O not present), so when using 64KB (65536 bytes) of External Memory, 61184 Bytes of External Memory are available in normal mode, and 61440 Bytes in ATmega103 compatibility mode. See

“External Memory Interface” on page 24 for details on how to take advantage of the

external memory map.

4000 up to 64K

2467B–09/01

When the addresses accessing the SRAM memory space exceeds the internal data memory locations, the external data SRAM is accessed using the same instructions as for the internal data memory access. When the internal data memories are accessed, the read and write strobe pins (PG0 and PG1) are inactive during the whole access cycle. External SRAM operation is enabled by setting the SRE bit in the MCUCR register.

Accessing external SRAM takes one additional clock cycle per byte compared to access of the internal SRAM. This means that the commands LD, ST, LDS, STS, LDD, STD, PUSH and POP take one additional clock cycle. If the stack is placed in external SRAM, interrupts, subroutine calls and returns take three clock cycles extra because the twobyte program counter is pushed and popped, and external memory access does not take advantage of the internal pipe-line memory access. When external SRAM interface is used with wait-state, one-byte external access takes two, three, or four additional clock cycles for one, two, and three wait-states respectively. Interrupt, subroutine calls and returns will need five, seven, or nine clock cycles more than specified in the instruction set manual for one, two, and three wait-states.

The five different addressing modes for the data memory cover: Direct, Indirect with 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 postincrement, the address registers X, Y, and Z are decremented or incremented.

The 32 general purpose working registers, 64 I/O registers, and the 4096 bytes of internal data SRAM in the ATmega128 are all accessible through all these addressing modes. The Register file is described in

“General Purpose Register File” on page 10.

Figure 9. Data Memory Map

Memory Configuration A

Data Memory

32 Registers

64 I/O Registers

160 Ext I/O Reg.

Internal SRAM

(4096 x 8)

External SRAM

(0 - 64K x 8)

$0000 - $001F $0020 - $005F $0060 - $00FF $0100

$10FF $1100

$FFFF

Memory Configuration B

Data Memory

32 Registers

64 I/O Registers

Internal SRAM

(4000 x 8)

External SRAM

(0 - 64K x 8)

$0000 - $001F $0020 - $005F $0060

$0FFF $1000

$FFFF

Data Memory Access Times This section describes the general access timing concepts for internal memory access.

The internal data SRAM access is performed in two clk

ATmega128(L)

cycles as described in Figure

CPU

2467B–09/01

Figure 10. On-chip Data SRAM Access Cycles

T1 T2 T3

clk

CPU

Address

Data

Compute Address

Address valid

ATmega128(L)

Write

Read

Memory access instruction

Next instruction

EEPROM Data Memory The ATmega128 contains 4K bytes of data EEPROM memory. It is organized as a sep-

arate 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 JTAG data downloading to the EEPROM, see

page 292 and page 297 respectively.

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 ever, 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

is likely to rise or fall slowly on power-up/down. This

causes the device for some period of time to run at a voltage lower than specified as minimum for the clock frequency used.

23.

for details on how to avoid problems in these situations.

See “Preventing EEPROM Corruption” on page

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.

Table 2. A self-timing function, how-

EEPROM Address Register – EEARH and EEARL

2467B–09/01

Bit 151413121110 9 8

––––EEAR11 EEAR10 EEAR9 EEAR8 EEARH

EEAR7 EEAR6 EEAR5 EEAR4 EEAR3 EEAR2 EEAR1 EEAR0 EEARL

76543210

Read/Write 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 R/W

Initial value 0 0 0 0 X X X X

XXXXXXXX

• Bits 15..12 - Res: Reserved Bits

These are reserved bits and will always read as zero. When writing to this address location, write these bits to zero for compatibility with future devices.

EEPROM Data Register – EEDR

EEPROM Control Register – EECR

• Bits 11..0 - EEAR11..0: EEPROM Address

The EEPROM Address Registers – EEARH and EEARL specify the EEPROM address in the 4K bytes EEPROM space. The EEPROM data bytes are addressed linearly between 0 and 4096. The initial value of EEAR is undefined. A proper value must be written before the EEPROM may be accessed.

Bit 76543210

MSB LSB EEDR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial value00000000

• 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.

Bit 76543210

––––EERIE EEMWE EEWE EERE

Read/Write R R R R R/W R/W R/W R/W

Initial value 0 0 0 0 0 0 X 0

EECR

• Bits 7..4 - Res: Reserved Bits

These bits are reserved bits in the ATmega128 and will always read as zero.

• Bit 3 - EERIE: EEPROM Ready Interrupt Enable

Writing EERIE to one enables the EEPROM Ready Interrupt if the I-bit in SREG is set. Writing EERIE to zero disables the interrupt. The EEPROM Ready interrupt generates a constant interrupt when EEWE is cleared.

• Bit 2 - EEMWE: EEPROM Master Write Enable

The EEMWE bit determines whether setting EEWE to one causes the EEPROM to be written. When EEMWE is written to one, writing EEWE to one within 4 clock cycles will write data to the EEPROM at the selected address. If EEMWE is zero, writing EEWE to one 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 set to write the value into the EEPROM. The EEMWE bit must be set when the 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 in SPMCR becomes zero.

3. Write new EEPROM address to EEAR (optional).

4. Write new EEPROM data to EEDR (optional).

5. Write a logical one to the EEMWE bit while writing a zero to EEWE in EECR.

6. Within four clock cycles after setting EEMWE, write a logical one to EEWE.

ATmega128(L)

2467B–09/01

ATmega128(L)

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

page 266

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 the 4 last 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.

• 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.

“Boot Loader Support – Read-While-Write Self-Programming” on

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 2 lists the typical

programming time for EEPROM access from the CPU.

Table 2. EEPROM Programming Time.

Symbol

EEPROM Write

(from CPU)

Number of Calibrated

RC Oscillator Cycles

Approximately 8300 7.5 ms 9.0 ms

Min Programming

Time

Max Programming

Time

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.

2467B–09/01

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);

}

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.

ATmega128(L)

2467B–09/01

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;

}

ATmega128(L)

Preventing EEPROM Corruption

During periods of low V

the EEPROM data can be corrupted because the supply volt-

CC,

age is too low for the CPU and the EEPROM to operate properly. These issues are the same as for board level systems using EEPROM, and the same design solutions should be applied.

An EEPROM data corruption can be caused by two situations when the voltage is too low. First, a regular write sequence to the EEPROM requires a minimum voltage to operate correctly. 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:

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

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.

2467B–09/01

I/O Memory The I/O space definition of the ATmega128 is shown in “Register Summary” on page

323

All ATmega128 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 $00 - $1F 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 chapter for more details. When using the I/O specific commands IN and OUT, the I/O addresses $00 - $3F must be used. When addressing I/O registers as data space using LD and ST instructions, $20 must be added to these addresses. The ATmega128 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 $60 - $FF in SRAM, only the ST/STS/STD and LD/LDS/LDD instructions can be used. The Extended I/O space is replaced with SRAM locations when the ATmega128 is in the ATmega103 compatibility mode.

For compatibility with future devices, reserved bits should be written to zero if accessed. Reserved I/O memory addresses should never be written.

Some of the status flags are cleared by writing a logical one to them. Note that the CBI and SBI instructions will operate on all bits in the I/O register, writing a one back into any flag read as set, thus clearing the flag. The CBI and SBI instructions work with registers $00 to $1F only.

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

External Memory Interface

Overview When the eXternal MEMory (XMEM) is enabled, address space outside the internal

With all the features the External Memory Interface provides, it is well suited to operate as an interface to memory devices such as external SRAM and Flash, and peripherals such as LCD-display, A/D, and D/A. The main features are:

• Four different wait-state settings (including no wait-state).

• Independent wait-state setting for different external memory sectors (configurable

sector size).

• The number of bits dedicated to address high byte is selectable.

• Bus keepers on data lines to minimize current consumption (optional).

SRAM becomes available using the dedicated external memory pins (see

page 2

memory configuration is shown in

, Table 27 on page 68, Table 33 on page 72, and Table 45 on page 80). The

Figure 11.

Figure 1 on

ATmega128(L)

2467B–09/01

Figure 11. External Memory with Sector Select

ATmega128(L)

External Memory

(0-60K x 8)

Memory Configuration A

Internal memory

Lower sector

SRW01 SRW00

Upper sector

SRW11 SRW10

0x0000

0x10FF 0x1100

SRL[2..0]

0xFFFF

Memory Configuration B

0x0000

Internal memory

0x0FFF 0x1000

SRW10

External Memory

(0-60K x 8)

0xFFFF

Note: ATmega128 in non ATmega103 compatibility mode: Memory Configuration A is available

(Memory Configuration B N/A) ATmega128 in ATmega103 compatibility mode: Memory Configuration B is available (Memory Configuration A N/A)

ATmega103 Compatibility Both External Memory Control Registers (XMCRA and XMCRB) are placed in Extended

I/O space. In ATmega103 Compatibility mode, these registers are not available, and the features selected by these registers are not available. The device is still ATmega103 compatible, as these features did not exist in ATmega103. The limitations in ATmega103 compatibility mode are:

• Only two wait-states settings are available (SRW1n = 0b00 and SRW1n = 0b01).

• The number of bits that are assigned to address high byte are fixed.

• The external memory section can not be divided into sectors with different wait-state

settings.

• Bus-keeper is not available. , WR and ALE pins are output only (Port G in ATmega128).

Using the External Memory Interface

• RD

The interface consists of:

• AD7:0: Multiplexed low-order address bus and data bus.

• A15:8: High-order address bus (configurable number of bits).

• ALE: Address latch enable.

• RD

: Read strobe.

• WR: Write strobe.

2467B–09/01

The control bits for the External Memory Interface are located in three registers, the MCU Control Register – MCUCR, the External Memory Control Register A – XMCRA, and the External Memory Control Register B – XMCRB.

When the XMEM interface is enabled, the XMEM interface will override the setting in the data direction registers that corresponds to the ports dedicated to the XMEM interface. For details about the port override, see the alternate functions in section

page 60

. The XMEM interface will auto-detect whether an access is internal or external.

“I/O-Ports” on

If the access is external, the XMEM interface will output address, data, and the control signals on the ports according to

Figure 13 (this figure shows the wave forms without

wait-states). When ALE goes from high-to-low, there is a valid address on AD7:0. ALE is low during a data transfer. When the XMEM interface is enabled, also an internal access will cause activity on address, data and ALE ports, but the RD

and WR strobes will not toggle during internal access. When the External Memory Interface is disabled, the normal pin and data direction settings are used. Note that when the XMEM interface is disabled, the address space above the internal SRAM boundary is not mapped into the internal SRAM.

Figure 12 illustrates how to connect an external SRAM to the AVR using

an octal latch (typically “74 x 573” or equivalent) which is transparent when G is high.

Address Latch Requirements Due to the high-speed operation of the XRAM interface, the address latch must be

selected with care for system frequencies above 8 MHz @ 4V and 4 MHz @ 2.7V. When operating at conditions above these frequencies, the typical old style 74HC series latch becomes inadequate. The external memory interface is designed in compliance to the 74AHC series latch. However, most latches can be used as long they comply with the main timing parameters. The main parameters for the address latch are:

• D to Q propagation delay (t

• Data setup time before G low (t

• Data (address) hold time after G low (

The external memory interface is designed to guaranty minimum address hold time after G is asserted low of t

Tables 138 through Tables 145 on pages 317 - 319. The D-to-Q propagation delay

ing”

) must be taken into consideration when calculating the access time requirement of

= 5 ns. Refer to t

LAXX_LD/tLLAXX_ST

the external component. The data setup time before G low (t address valid to ALE low (t

) minus PCB wiring delay (dependent on the capacitive

AVLLC

in “External Data Memory Tim-

) must not exceed

load).

Figure 12. External SRAM Connected to the AVR

D[7:0]

AD7:0

AVR

ALE

A15:8

A[7:0]

SRAM

A[15:8]

RD WR

Pull-up and Bus-keeper The pull-ups on the AD7:0 ports may be activated if the corresponding Port register is

written to one. To reduce power consumption in sleep mode, it is recommended to disable the pull-ups by writing the Port register to zero before entering sleep.

ATmega128(L)

2467B–09/01

ATmega128(L)

The XMEM interface also provides a bus-keeper on the AD7:0 lines. The bus-keeper can be disabled and enabled in software as described in

ister B – XMCRB” on page 31

. When enabled, the bus-keeper will keep the previous

value on the AD7:0 bus while these lines are tri-stated by the XMEM interface.

If neither bus-keeper nor pull-ups are enabled, the XMEM interface will leave the AD7:0 tri-stated during a read access until the next RAM access (internal or external) appears.

Timing External memory devices have different timing requirements. To meet these require-

ments, the ATmega128 XMEM interface provides four different wait-states as shown in

Table 4. It is important to consider the timing specification of the external memory

device before selecting the wait-state. The most important parameters are the access time for the external memory compared to the set-up requirement of the ATmega128. The access time for the external memory is defined to be the time from receiving the chip select/address until the data of this address actually is driven on the bus. The access time cannot exceed the time from the ALE pulse must be asserted low until data is stable during a read sequence (See t

145

on pages 317 - 319). The different wait-states are set up in software. As an addi-

LLRL

+ t

RLRH

tional feature, it is possible to divide the external memory space in two sectors with individual wait-state settings. This makes it possible to connect two different memory devices with different timing requirements to the same XMEM interface. For XMEM interface timing details, please refer to

159

in the “External Data Memory Timing” on page 317.

Table 138 to Table 145 and Figure 156 to Figure

“External Memory Control Reg-

- t

in Tables 138 through Tables

DVRH

Note that the XMEM interface is asynchronous and that the waveforms in the following figures are related to the internal system clock. The skew between the internal and external clock (XTAL1) is not guarantied (varies between devices temperature, and supply voltage). Consequently, the XMEM interface is not suited for synchronous operation.

Figure 13. External Data Memory Cycles without Wait-state (SRWn1 = 0 and SRWn0 = 0)

System Clock (CLK

DA7:0 (XMBK = 0)

DA7:0 (XMBK = 1)

CPU

ALE

A15:8

DA7:0

)

(1)

T1 T2 T3

AddressPrev. addr.

Address DataPrev. data XX

Write

DataPrev. data Address

Read

2467B–09/01

Note: 1. SRWn1 = SRW11 (upper sector) or SRW01 (lower sector), SRWn0 = SRW10 (upper

sector) or SRW00 (lower sector). The ALE pulse in period T4 is only present if the next instruction accesses the RAM (internal or external).

Figure 14. External Data Memory Cycles with SRWn1 = 0 and SRWn0 = 1

(1)

System Clock (CLK

DA7:0 (XMBK = 0)

DA7:0 (XMBK = 1)

CPU

ALE

A15:8

DA7:0

T1 T2 T3

)

AddressPrev. addr.

Address DataPrev. data XX

DataPrev. data Address

Write

Read

Note: 1. SRWn1 = SRW11 (upper sector) or SRW01 (lower sector), SRWn0 = SRW10 (upper

sector) or SRW00 (lower sector). The ALE pulse in period T5 is only present if the next instruction accesses the RAM (internal or external).

Figure 15. External Data Memory Cycles with SRWn1 = 1 and SRWn0 = 0

System Clock (CLK

CPU

T1 T2 T3

)

T4 T5

(1)

ALE

A15:8

DA7:0

DA7:0 (XMBK = 0)

DA7:0 (XMBK = 1)

Address DataPrev. data XX

AddressPrev. addr.

DataPrev. data Address

Note: 1. SRWn1 = SRW11 (upper sector) or SRW01 (lower sector), SRWn0 = SRW10 (upper

sector) or SRW00 (lower sector). The ALE pulse in period T6 is only present if the next instruction accesses the RAM (internal or external).

Write

Read

ATmega128(L)

2467B–09/01

ATmega128(L)

XMEM Register Description

MCU Control Register – MCUCR

Figure 16. External Data Memory Cycles with SRWn1 = 1 and SRWn0 = 1

System Clock (CLK

DA7:0 (XMBK = 0)

DA7:0 (XMBK = 1)

CPU

ALE

A15:8

DA7:0

)

T1 T2 T3

AddressPrev. addr.

Address DataPrev. data XX

DataPrev. data Address

T4 T5 T6

(1)

Note: 1. SRWn1 = SRW11 (upper sector) or SRW01 (lower sector), SRWn0 = SRW10 (upper

sector) or SRW00 (lower sector). The ALE pulse in period T7 is only present if the next instruction accesses the RAM (internal or external).

Bit 76543210

SRE SRW10

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial value00000000

SE SM1 SM0 SM2 IVSEL IVCE MCUCR

Write

Read

External Memory Control Register A – XMCRA

• Bit 7 - SRE: External SRAM/XMEM Enable

Writing SRE to one enables the External Memory Interface.The pin functions AD7:0, A15:8, ALE, WR

, and RD are activated as the alternate pin functions. The SRE bit overrides any pin direction settings in the respective data direction registers. Writing SRE to zero, disables the External Memory Interface and the normal pin and data direction settings are used.

• Bit 6 - SRW10: Wait-state Select Bit

For a detailed description in non-ATmega103 Compatibility mode, see common description for the SRWn bits below (XMCRA description). In ATmega103 Compatibility mode, writing SRW10 to one enables the wait-state and one extra cycle is added during read/write strobe as shown in

Bit 76543210

- SRL2 SRL1 SRL0 SRW01 SRW00 SRW11 - XMCRA

Read/Write R R/W R/W R/W R/W R/W R/W R

Initial value00000000

Figure 14.

• Bit 7 - Res: Reserved Bit

This is a reserved bit and will always read as zero. When writing to this address location, write this bit to zero for compatibility with future devices.

2467B–09/01

• Bit 6..4 - SRL2, SRL1, SRL0: Wait-state Sector Limit

It is possible to configure different wait-states for different external memory addresses. The external memory address space can be divided in two sectors that have separate wait-state bits. The SRL2, SRL1, and SRL0 bits select the split of the sectors, see

and Figure 11. By default, the SRL2, SRL1, and SRL0 bits are set to zero and the

Table

entire external memory address space is treated as one sector. When the entire SRAM address space is configured as one sector, the wait-states are configured by the SRW11 and SRW10 bits.

Table 3. Sector limits with different settings of SRL2..0

SRL2 SRL1 SRL0 Sector Limits

0 0 0 Lower sector = N/A

Upper sector = 0x1100-0xFFFF

0 0 1 Lower sector = 0x1100-0x1FFF

Upper sector = 0x2000-0xFFFF

0 1 0 Lower sector = 0x1100-0x3FFF

Upper sector = 0x4000-0xFFFF

0 1 1 Lower sector = 0x1100-0x5FFF

Upper sector = 0x6000-0xFFFF

1 0 0 Lower sector = 0x1100-0x7FFF

Upper sector = 0x8000-0xFFFF

1 0 1 Lower sector = 0x1100-0x9FFF

Upper sector = 0xA000-0xFFFF

1 1 0 Lower sector = 0x1100-0xBFFF

Upper sector = 0xC000-0xFFFF

1 1 1 Lower sector = 0x1100-0xDFFF

Upper sector = 0xE000-0xFFFF

• Bit 1 and Bit 6 MCUCR - SRW11, SRW10: Wait-state Select Bits for Upper Sector

The SRW11 and SRW10 bits control the number of wait-states for the upper sector of the external memory address space, see

Table 4.

• Bit 3..2 - SRW01, SRW00: Wait-state Select Bits for Lower Sector

The SRW01 and SRW00 bits control the number of wait-states for the lower sector of the external memory address space, see

Table 4. Wait States

SRWn1 SRWn0 Wait States

0 0 No wait-states

0 1 Wait one cycle during read/write strobe

1 0 Wait two cycles during read/write strobe

1 1 Wait two cycles during read/write and wait one cycle before driving out

Note: 1. n = 0 or 1 (lower/upper sector).

For further details of the timing and wait-states of the External Memory Interface, see Figures 13 through Figures 16 for how the setting of the SRW bits affects the timing.

(1)

new address

Table 4.

ATmega128(L)

2467B–09/01

External Memory Control Register B – XMCRB

ATmega128(L)

• Bit 0 - Res: Reserved Bit

This is a reserved bit and will always read as zero. When writing to this address location, write this bit to zero for compatibility with future devices.

Bit 76543210

XMBK ––––XMM2 XMM1 XMM0 XMCRB

Read/WriteR/WRRRRR/WR/WR/W

Initial value00000000

• Bit 7- XMBK: External Memory Bus-keeper Enable

Writing XMBK to one enables the bus keeper on the AD7:0 lines. When the bus keeper is enabled, AD7:0 will keep the last driven value on the lines even if the XMEM interface has tri-stated the lines. Writing XMBK to zero disables the bus keeper. XMBK is not qualified with SRE, so even if the XMEM interface is disabled, the bus keepers are still activated as long as XMBK is one.

• Bit 6..4 - Res: Reserved Bits

These are reserved bits and will always read as zero. When writing to this address location, write these bits to zero for compatibility with future devices.

• Bit 2..0 - XMM2, XMM1, XMM0: External Memory High Mask

When the External Memory is enabled, all Port C pins are default used for the high address byte. If the full 60KB address space is not required to access the external memory, some, or all, Port C pins can be released for normal Port Pin function as described

Table 5. As described in “Using all 64KB Locations of External Memory” on page 32,

in it is possible to use the XMMn bits to access all 64KB locations of the external memory.

Table 5 . Port C Pins Released as Normal Port Pins when the External Memory is Enabled

XMM2 XMM1 XMM0 # Bits for External Memory Address Released Port Pins

0 0 0 8 (Full 60 KB space) None

0017 PC7

0106 PC7 - PC6

0115 PC7 - PC5

1004 PC7 - PC4

1013 PC7 - PC3

1102 PC7 - PC2

1 1 1 No Address high bits Full Port C

2467B–09/01

Using all 64KB Locations of External Memory

Since the external memory is mapped after the internal memory as shown in Figure 11, only 60KB of external memory is available by default (address space 0x0000 to 0x10FF is reserved for internal memory). However, it is possible to take advantage of the entire external memory by masking the higher address bits to zero. This can be done by using the XMMn bits and control by software the most significant bits of the address. By setting Port C to output 0x00, and releasing the most significant bits for normal Port Pin operation, the Memory Interface will address 0x0000-0x1FFF. See the following code examples.

Assembly Code Example

; OFFSET is defined to 0x2000 to ensure ; external memory access ; Configure Port C (address high byte) to ; output 0x00 when the pins are released ; for normal Port Pin operation

ldi r16, 0xFF out DDRC, r16 ldi r16, 0x00 out PORTC, r16

; release PC7:5

ldi r16, (1<<XMM1)|(1<<XMM0) sts XMCRB, r16

; write 0xAA to address 0x0001 of external ; memory

ldi r16, 0xaa sts 0x0001+OFFSET, r16

; re-enable PC7:5 for external memory

ldi r16, (0<<XMM1)|(0<<XMM0) sts XMCRB, r16

; store 0x55 to address (OFFSET + 1) of ; external memory

ldi r16, 0x55 sts 0x0001+OFFSET, r16

C Code Example

#define OFFSET 0x2000

(1)

void XRAM_example(void) { unsigned char *p = (unsigned char *) (OFFSET + 1);

DDRC = 0xFF; PORTC = 0x00;

XMCRB = (1<<XMM1) | (1<<XMM0);

*p = 0xaa;

XMCRB = 0x00;

*p = 0x55; }

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

Care must be exercised using this option as most of the memory is masked away.

ATmega128(L)

2467B–09/01

System Clock and Clock Options

ATmega128(L)

Clock Systems and their Distribution

Figure 17 presents the principal clock systems in the AVR and their distribution. All of

the clocks need not be active at a given time. In order to reduce power consumption, the clocks to modules not being used can be halted by using different sleep modes, as described in

“Power Management and Sleep Modes” on page 41. The clock systems

are detailed below.

Figure 17. Clock Distribution

Asynchronous Timer/Counter

General I/O

modules

clk

I/O

clk

ASY

ADC CPU Core RAM

clk

ADC

AVR Clock

Control Unit

Source clock

Clock

Multiplexer

clk

CPU

clk

FLASH

Reset Logic

Watchdog clock

Watchdog Timer

Watchdog

Oscillator

Flash and EEPROM

CPU Clock – clk

I/O Clock – clk

I/O

Flash Clock – clk

2467B–09/01

CPU

FLASH

Timer/Counter

Oscillator

External RC

Oscillator

External clock

Crystal

Oscillator

Low-Frequency

Crystal Oscillator

Calibrated RC

Oscillator

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.

The I/O clock is used by the majority of the I/O modules, like Timer/Counters, SPI, and USART. The I/O clock is also used by the External Interrupt module, but note that some external interrupts are detected by asynchronous logic, allowing such interrupts to be detected even if the I/O clock is halted. Also note that address recognition in the TWI module is carried out asynchronously when clk

is halted, enabling TWI address recep-

I/O

tion in all sleep modes.

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

Asynchronous Timer Clock – clk

ASY

The Asynchronous Timer clock allows the Asynchronous Timer/Counter to be clocked directly from an external 32 kHz clock crystal. The dedicated clock domain allows using this Timer/Counter as a real-time counter even when the device is in sleep mode.

ADC Clock – clk

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.

Clock Sources The device has the following clock source options, selectable by Flash fuse bits as

shown below. The clock from the selected source is input to the AVR clock generator, and routed to the appropriate modules.

Table 6. Device Clocking Options Select

Device Clocking Option CKSEL3..0

External Crystal/Ceramic Resonator 1111 - 1010

External Low-frequency Crystal 1001

External RC Oscillator 1000 - 0101

Calibrated Internal RC Oscillator 0100 - 0001

External Clock 0000

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

The various choices for each clocking option is given in the following sections. When the CPU wakes up from power down or power save, the selected clock source is used to time the start-up, ensuring stable oscillator operation before instruction execution starts. When the CPU starts from reset, there is as an additional delay allowing the power to reach a stable level before commencing 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 lator is voltage dependent as shown in the

Preliminary Data” on page 322

. The device is shipped with CKSEL = “0001” and SUT =

Table 7. The frequency of the watchdog oscil-

“ATmega128 Typical Characteristics –

“10” (1 MHz Internal RC Oscillator, slowly rising power).

(1)

Table 7. Number of Watchdog Oscillator Cycles

Time-out (VCC = 5.0V) Time-Out (VCC = 3.0V) Number of Cycles

(1)

4 ms

(1)

64 ms

Note: 1. Values are guidelines only. Actual values are TBD.

4 ms

64 ms

(1)

64K

Crystal Oscillator XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can

Figure 18. Either a quartz

2467B–09/01

be configured for use as an on-chip oscillator, as shown in crystal or a ceramic resonator may be used. The CKOPT fuse selects between two different oscillator amplifier modes. When CKOPT is programmed, the oscillator output will oscillate will a full rail-to-rail swing on the output. This mode is suitable when operating in a very noisy environment or when the output from XTAL2 drives a second clock buffer. This mode has a wide frequency range. When CKOPT is unprogrammed, the oscillator has a smaller output swing. This reduces power consumption considerably. This mode has a limited frequency range and it can not be used to drive other clock buffers.

ATmega128(L)

For resonators, the maximum frequency is 8 MHz with CKOPT unprogrammed and 16 MHz with CKOPT programmed. 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 8. 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 18. Crystal Oscillator Connections

XTAL2

XTAL1

GND

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 8.

Table 8. Crystal Oscillator Operating Modes

Frequency Range

CKOPT CKSEL3..1

1 101

1 110 0.9 - 3.0 12 pF - 22 pF

1 111 3.0 - 8.0 12 pF - 22 pF

0 101, 110, 111 1.0 - 12 pF - 22 pF

(2)

(MHz)

0.4 - 0.9 –

(1)

Recommended Range for Capacitors

C1 and C2 for Use with Crystals

2467B–09/01

Notes: 1. The frequency ranges are preliminary values. Actual values are TBD.

2. 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 9.

Table 9. Start-up Times for the Crystal Oscillator Clock Selection

Start-up Time from

Power-down and

CKSEL0 SUT1..0

Notes: 1. These options should only be used when not operating close to the maximum fre-

2. These options are intended for use with ceramic resonators and will ensure fre-

00 258 CK

01 258 CK

10 1K CK

11 1K CK

00 1K CK

01 16K CK - Crystal oscillator, BOD

10 16K CK 4 ms Crystal oscillator, fast

11 16K CK 64 ms Crystal oscillator,

quency of the device, and only if frequency stability at start-up is not important for the application. These options are not suitable for crystals.

quency 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.

Power-save

(1)

(2)

Additional Delay

from Reset

(VCC = 5.0V) Recommended Usage

4 ms Ceramic resonator, fast

rising power

64 ms Ceramic resonator,

slowly rising power

– Ceramic resonator,

BOD enabled

4 ms Ceramic resonator, fast

rising power

64 ms Ceramic resonator,

slowly rising power

enabled

rising power

slowly rising power

Low-frequency Crystal Oscillator

ATmega128(L)

To use a 32.768 kHz watch crystal as the clock source for the device, the low-frequency crystal oscillator must be selected by setting the CKSEL fuses to “1001”. The crystal should be connected as shown in

Figure 18. By programming the CKOPT fuse, the user

can enable internal capacitors on XTAL1 and XTAL2, thereby removing the need for external capacitors. The internal capacitors have a nominal value of 36 pF. Refer to the 32 kHz Crystal Oscillator application note for details on oscillator operation and how to choose appropriate values for C1 and C2.

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

Table 10.

Table 10. Start-up Times for the low Frequency Crystal Oscillator Clock Selection

Start-up Time from

Power-down and

SUT1..0

00 1K CK

01 1K CK

10 32K CK 64 ms Stable frequency at start-up

11 Reserved

Power-save

(1)

Additional Delay

from Reset

= 5.0V) Recommended Usage

4 ms Fast rising power or BOD enabled

64 ms Slowly rising power

2467B–09/01

ATmega128(L)

Note: 1. These options should only be used if frequency stability at start-up is not important

for the application.

External RC Oscillator For timing insensitive applications, the external RC configuration shown in Figure 19

can be used. The frequency is roughly estimated by the equation f = 1/(3RC). C should be at least 22 pF. By programming the CKOPT fuse, the user can enable an internal 36 pF capacitor between XTAL1 and GND, thereby removing the need for an external capacitor. For more information on oscillator operation and details on how to choose R and C, refer to the External RC Oscillator Application Note.

Figure 19. External RC Configuration

XTAL2

XTAL1

GND

The oscillator can operate in four different modes, each optimized for a specific frequency range. The operating mode is selected by the fuses CKSEL3..0 as shown in

Table 11.

Table 11. External RC Oscillator Operating Modes

CKSEL3..0 Frequency Range (MHz)

0101 - 0.9

0110 0.9 - 3.0

0111 3.0 - 8.0

1000 8.0 - 12.0

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

Table 12.

2467B–09/01

Table 12. Start-Up Times for the External RC Oscillator Clock Selection

Start-up Time from

Power-down and

SUT1..0

00 18 CK - BOD enabled

01 18 CK 4 ms Fast rising power

10 18 CK 64 ms Slowly rising power

11 6 CK

Note: 1. This option should not be used when operating close to the maximum frequency of

Power-save

(1)

the device.

Additional Delay

from Reset

(VCC = 5.0V) Recommended usage

4 ms Fast rising power or BOD enabled

Calibrated Internal RC Oscillator

The calibrated internal RC oscillator provides a fixed 1.0 MHz, 2.0 MHz, 4.0 MHz, or 8.0 MHz clock. All frequencies are nominal values at 5V and 25 selected as the system clock by programming the CKSEL fuses as shown in

°C. This clock may be

Table 13. If

selected, it will operate with no external components. The CKOPT fuse should always be unprogrammed when using this clock option. During reset, hardware loads the calibration byte into the OSCCAL register and thereby automatically calibrates the RC oscillator. At 5V, 25 frequency within

°C and 1.0 MHz oscillator frequency selected, this calibration gives a

± 1% of the nominal frequency. 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

“Calibration Byte” on page 282.

Table 13. Internal Calibrated RC Oscillator Operating Modes

CKSEL3..0 Nominal Frequency (MHz)

(1)

0001

0010 2.0

0011 4.0

0100 8.0

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

1.0

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

Table 14. XTAL1 and XTAL2 should be left unconnected (NC).

Oscillator Calibration Register – OSCCAL

Table 14. Start-up Times for the Internal Calibrated RC Oscillator Clock Selection

Start-up Time from Power-

SUT1..0

00 6 CK - BOD enabled

01 6 CK 4 ms Fast rising power

(1)

11 Reserved

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

Bit 76543210

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial value Device specific calibration value

Note: OSCCAL register is not available in ATmega103 compatibility mode.

down and Power-save

6 CK 64 ms Slowly rising power

CAL7 CAL6 CAL5 CAL4 CAL3 CAL2 CAL1 CAL0 OSCCAL

Additional Delay from

Reset (VCC = 5.0V) Recommended Usage

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

Writing the calibration byte to this address will trim the internal oscillator to remove process variations from the oscillator frequency. This is done automatically during chip reset. When OSCCAL is zero, the lowest available frequency is chosen. Writing nonzero values to this register will increase the frequency of the internal oscillator. Writing $FF to the register gives the highest available frequency. The calibrated oscillator is used to time EEPROM and Flash access. If EEPROM or Flash is written, do not calibrate to more than 10% above the nominal frequency. Otherwise, the EEPROM or Flash write may fail. Note that the Oscillator is intended for calibration to 1.0 MHz, 2.0 MHz,

4.0 MHz, or 8.0 MHz. Tuning to other values is not guaranteed, as indicated in

Table 15.

ATmega128(L)

2467B–09/01

Table 15. Internal RC Oscillator Frequency Range.

ATmega128(L)

Min Frequency in Percentage of

OSCCAL Value

$00 50 100

$7F 75 150

$FF 100 200

Nominal Frequency (%)

Max Frequency in Percentage of

Nominal Frequency (%)

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

Figure 20. To run the device on an external clock, the CKSEL fuses must be pro-

grammed to “0000”. By programming the CKOPT fuse, the user can enable an internal 36 pF capacitor between XTAL1 and GND.

Figure 20. External Clock Drive Configuration

EXTERNAL

CLOCK SIGNAL

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

Table 16.

Table 16. Start-up Times for the External Clock Selection

Start-up Time from Power-

SUT1..0

00 6 CK – BOD enabled

01 6 CK 4 ms Fast rising power

10 6 CK 64 ms Slowly rising power

11 Reserved

down and Power-save

Additional Delay from

Reset (VCC = 5.0V) Recommended Usage

Timer/Counter Oscillator For AVR microcontrollers with Timer/Counter Oscillator pins (TOSC1 and TOSC2), the

crystal is connected directly between the pins. No external capacitors are needed. The oscillator is optimized for use with a 32.768 kHz watch crystal. Applying an external clock source to TOSC1 is not recommended.

XTAL Divide Control Register – XDIV

The XTAL Divide Control Register is used to divide the Source clock frequency by a number in the range 2 - 129. This feature can be used to decrease power consumption when the requirement for processing power is low.

Bit 76543210

XDIVEN XDIV6 XDIV5 XDIV4 XDIV3 XDIV2 XDIV1 XDIV0 XDIV

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial value00000000

2467B–09/01

• Bit 7 - XDIVEN: XTAL Divide Enable

When the XDIVEN bit is written one, the clock frequency of the CPU and all peripherals (clk

I/O

, clk

ADC

, clk

CPU

, clk

) is divided by the factor defined by the setting of XDIV6 -

FLASH

XDIV0. This bit can be written run-time to vary the clock frequency as suitable to the application.

• Bits 6..0 - XDIV6..XDIV0: XTAL Divide Select Bits 6 - 0

These bits define the division factor that applies when the XDIVEN bit is set (one). If the value of these bits is denoted d, the following formula defines the resulting CPU and peripherals clock frequency f

CLK

Source clock

CLK

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

129

d–

The value of these bits can only be changed when XDIVEN is zero. When XDIVEN is written to one, the value written simultaneously into XDIV6..XDIV0 is taken as the division factor. When XDIVEN is written to zero, the value written simultaneously into XDIV6..XDIV0 is rejected. As the divider divides the master clock input to the MCU, the speed of all peripherals is reduced when a division factor is used.

ATmega128(L)

2467B–09/01

ATmega128(L)

Power Management and Sleep Modes

MCU Control Register – MCUCR

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 six sleep modes, the SE bit in MCUCR must be written to logic one and a SLEEP instruction must be executed. The SM2, SM1, and SM0 bits in the MCUCR register select which sleep mode (Idle, ADC Noise Reduction, Power-down, Power-save, Standby, or Extended Standby) will be activated by the SLEEP instruction.

Table 17 for a summary. If an enabled interrupt occurs while the MCU is in a sleep

See mode, the MCU wakes up. The MCU is then halted for four cycles in addition to the start-up time, it 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 17 on page 33 presents the different clock systems in the ATmega128, and their

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

The MCU Control Register contains control bits for power management.

Bit 76543210

SRE SRW10 SE SM1 SM0 SM2 IVSEL IVCE MCUCR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial value00000000

• Bit 5 - SE: Sleep Enable

The SE bit must be written to logic one to make the MCU enter the sleep mode when the SLEEP instruction is executed. To avoid the MCU entering the sleep mode unless it is the programmers 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.

• Bits 4..2 - SM2..0: Sleep Mode Select Bits 2, 1, and 0

These bits select between the six available sleep modes as shown in

Table 17.

Table 17. Sleep Mode Select

SM2 SM1 SM0 Sleep Mode

000Idle

0 0 1 ADC Noise Reduction

010Power-down

011Power-save

100Reserved

101Reserved

110Standby

1 1 1 Extended Standby

Note: 1. Standby Mode and Extended Standby Mode are only available with external crystals

or resonators.

(1)

2467B–09/01

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, USART, Analog Comparator, ADC, 2wire Serial Interface, Timer/Counters, Watchdog, and the interrupt system to continue operating. This sleep mode basically halts clk clocks to run.

Idle mode enables the MCU to wake up from external triggered interrupts as well as internal ones like the Timer Overflow and USART Transmit Complete interrupts. If wake-up from the Analog Comparator interrupt is not required, the Analog Comparator can be powered down by setting the ACD bit in the Analog Comparator Control and Status register – ACSR. This will reduce power consumption in Idle Mode. If the ADC is enabled, a conversion starts automatically when this mode is entered.

CPU

and clk

, while allowing the other

FLASH

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, the 2-wire Serial Interface address watch, Timer/Counter0 and the Watchdog to continue operating (if enabled). This sleep mode basically halts clk clk

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 form the ADC Conversion Complete interrupt, only an external reset, a watchdog reset, a brown-out reset, a 2-wire Serial Interface address match interrupt, a Timer/Counter0 interrupt, an SPM/EEPROM ready interrupt, an external level interrupt on INT7:4, or an external interrupt on INT3:0 can wake up the MCU from ADC Noise Reduction Mode.

, while allowing the other clocks to run.

FLASH

I/O

, clk

CPU

, and

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, the 2-wire Serial Interface address watch, and the Watchdog continue operating (if enabled). Only an external reset, a watchdog reset, a brown-out reset, a 2-wire Serial Interface address match interrupt, an external level interrupt on INT7:4, or an external 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

rupts” on page 84

for details.

“External Inter-

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 34.

Power-save Mode When the SM2..0 bits are written to 011, the SLEEP instruction makes the MCU enter

Power-save Mode. This mode is identical to Power-down, with one exception:

If Timer/Counter0 is clocked asynchronously, i.e., the AS0 bit in ASSR is set, Timer/Counter0 will run during sleep. The device can wake up from either Timer Overflow or Output Compare event from Timer/Counter0 if the corresponding Timer/Counter0 interrupt enable bits are set in TIMSK, and the global interrupt enable bit in SREG is set.

If the asynchronous timer is NOT clocked asynchronously, Power-down mode is recommended instead of Power-save Mode because the contents of the registers in the

ATmega128(L)

2467B–09/01

ATmega128(L)

asynchronous timer should be considered undefined after wake-up in Power-save Mode if AS0 is 0.

This sleep mode basically halts all clocks except clk

, allowing operation only of asyn-

ASY

chronous modules, including Timer/Counter0 if clocked asynchronously.

Standby Mode When the SM2..0 bits are 110 and an external crystal/resonator clock option is selected,

the SLEEP instruction makes the MCU enter Standby Mode. This mode is identical to Power-down with the exception that the oscillator is kept running. From Standby Mode, the device wakes up in 6 clock cycles.

Extended Standby Mode When the SM2..0 bits are 111 and an external crystal/resonator clock option is selected,

the SLEEP instruction makes the MCU enter Extended Standby Mode. This mode is identical to Power-save Mode with the exception that the oscillator is kept running. From Extended Standby Mode, the device wakes up in 6 clock cycles.

Table 18. Active Clock Domains and Wake Up Sources in the Different Sleep Modes

Active Clock Domains Oscillators Wake Up Sources

Main Clock

ASY

Source

Enabled

Sleep Mode clk

CPU

clk

FLASH

clkIOclk

ADC

clk

Idle X X X X X

ADC Noise

XX X X

Reduction

Power Down

Timer

Osc

Enabled INT7:0

(2)

XX X XXX

(3)

TWI

Address

Match Timer 0

SPM/

EEPROM

Ready ADC

XX XX

Other

I/O

Power Save

Standby

Extended Standby

(1)

(2)

Notes: 1. External Crystal or resonator selected as clock source

2. If AS

0 bit in ASSR is set

3. Only INT3:0 or level interrupt INT7:4

(2)

(3)

(2)

2467B–09/01

Minimizing Power Consumption

Analog to Digital Converter If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should

Analog Comparator When entering Idle Mode, the Analog Comparator should be disabled if not used. When

Brown-out Detector If the Brown-out Detector is not needed in the application, this module should be turned

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.

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

verter” on page 221

entering ADC Noise Reduction Mode, the Analog Comparator should be disabled. In the 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

page 218

off. If the Brown-out Detector is enabled by the BODEN fuse, 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

on page 44

for details on how to configure the Analog Comparator.

for details on how to configure the Brown-out Detector.

for details on ADC operation.

“Analog to Digital Con-

“Analog Comparator” on

“Brown-out Detector”

Internal Voltage Reference The Internal Voltage Reference will be enabled when needed by the Brown-out detec-

tor, 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 start-up time.

Watchdog Timer If the Watchdog Timer is not needed in the application, this module should be turned off.

If the Watchdog Timer is enabled, it will be enabled in all sleep modes, and hence, always consume power. In the deeper sleep modes, this will contribute significantly to the total current consumption. Refer to to configure the Watchdog Timer.

Port Pins When entering a sleep mode, all port pins should be configured to use minimum power.

The most important thing is then to ensure that no pins drive resistive loads. In sleep modes where the both the I/O clock (clk input buffers of the device will be disabled. This ensures that no power is consumed by the input logic when not needed. In some cases, the input logic is needed for detecting wake-up conditions, and it will then be enabled. Refer to the section

Enable and Sleep Modes” on page 65

buffer is enabled and the input signal is left floating or have an analog signal level close

/2, the input buffer will use excessive power.

to V

“Internal Voltage Reference” on page 49 for details on the

“Watchdog Timer” on page 50 for details on how

) and the ADC clock (clk

I/O

for details on which pins are enabled. If the input

) are stopped, the

ADC

“Digital Input

ATmega128(L)

2467B–09/01

ATmega128(L)

System Control and Reset

Resetting the AVR During reset, all I/O registers are set to their initial values, and the program starts execu-

tion 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 the reset circuitry.

The I/O ports of the AVR are immediately reset to their initial state when a reset source goes active. This does not require any clock source to be running.

After all reset sources have gone inactive, a delay counter is invoked, stretching the internal reset. This allows the power to reach a stable level before normal operation starts. The time-out period of the delay counter is defined by the user through the CKSEL fuses. The different selections for the delay period are presented in

Sources” on page 34

Reset Sources The ATmega128 has five sources of reset:

• Power-on Reset. The MCU is reset when the supply voltage is below the power-on

• External Reset. The MCU is reset when a low level is present on the RESET pin for

• Watchdog Reset. The MCU is reset when the Watchdog timer period expires and

• Brown-out Reset. The MCU is reset when the supply voltage V

• JTAG AVR Reset. The MCU is reset as long as there is a logic one in the Reset

Figure 21 shows the reset logic. Table 19 defines the electrical parameters of

reset threshold (V

longer than the minimum pulse length.

the Watchdog is enabled.

brown-out reset threshold (V

1149.1 (JTAG) Boundary-scan” on page 244

POT

is below the

) and the Brown-out Detector is enabled.

BOT

for details.

“Clock

“IEEE

2467B–09/01

Figure 21. Reset Logic

DATA BUS

PEN

BODEN

BODLEVEL

RESET

Pull-up Resistor

Power-On Reset

Circuit

Pull-up Resistor

SPIKE

FILTER

JTAG Reset

MCU Control and Status

JTRF

BORF

PORF

WDRF

EXTRF

Brown-Out

Reset Circuit

Watchdog

Timer

Watchdog

Oscillator

Clock

Generator

Delay Counters

COUNTER RESET

TIMEOUT

CKSEL[3:0]

SUT[1:0]

Table 19. Reset Characteristics

(1)

Symbol Parameter Condition Min Typ Max Units

POT

RST

BOT

BOD

HYST

Power-on Reset Threshold Voltage (rising)

Power-on Reset Threshold Voltage (falling)

(2)

RESET Pin Threshold Voltage TBD TBD TBD V

Minimum pulse width on

RESET

Brown-out Reset Threshold Vol ta ge

Minimum low voltage period for Brown-out Detection

BODLEVEL = 1 TBD 2.7 TBD

BODLEVEL = 0 TBD 4.0 TBD

BODLEVEL = 1 TBD TBD TBD µs

BODLEVEL = 0 TBD TBD TBD µs

Brown-out Detector hysteresis TBD 50 TBD mV

TBD TBD 2.3 V

TBD TBD TBD ns

Notes: 1. Values are guidelines only. Actual values are TBD.

2. The Power-on Reset will not work unless the supply voltage has been below V (falling)

POT

ATmega128(L)

2467B–09/01

ATmega128(L)

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

tion level is defined in

Table 19. The POR is activated whenever V

detection level. The POR circuit can be used to trigger the start-up reset, as well as to detect a failure in supply voltage.

A Power-on Reset (POR) circuit ensures that the device is reset from power-on. Reaching the power-on reset threshold voltage invokes the delay counter, which determines how long the device is kept in RESET after V again, without any delay, when V

decreases below the detection level.

rise. The RESET signal is activated

is below the

Figure 22. MCU Start-up, RESET

RESET

TIME-OUT

INTERNAL

RESET

POT

RST

TOUT

Figure 23. MCU Start-up, RESET

RESET

TIME-OUT

POT

Tied to VCC.

Extended Externally

RST

TOUT

INTERNAL

RESET

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

than the minimum pulse width (see

Table 19) 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 counter starts the MCU after the Time-out period t

2467B–09/01

on its positive edge, the delay

RST

has expired.

TOUT

pin. Reset pulses longer

Figure 24. External Reset During Operation

Brown-out Detection ATmega128 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 fuse BODLEVEL to be 2.7V (BODLEVEL unprogrammed), or 4.0V (BODLEVEL programmed). The trigger level has a hysteresis to ensure spike free brown-out detection. The hysteresis on the detection level should be interpreted as V

BOT+

= V

BOT

+ V

HYST

/2 and V

BOT-

= V

BOT

- V

HYST

/2.

The BOD circuit can be enabled/disabled by the fuse BODEN. When the BOD is enabled (BODEN programmed), and V

in Figure 25), the Brown-out reset is immediately activated. When VCC increases

BOT-

above the trigger level (V time-out period t

has expired.

TOUT

in Figure 25), the delay counter starts the MCU after the

BOT+

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

given in Table 19.

BOD

decreases to a value below the trigger level

if the voltage stays below the trigger level

Figure 25. Brown-out Reset During Operation

RESET

TIME-OUT

BOT-

BOT+

TOUT

INTERNAL

RESET

Watchdog Reset When the Watchdog times out, it will generate a short reset pulse of 1 CK cycle dura-

tion. On the falling edge of this pulse, the delay timer starts counting the Time-out period

. Refer to page 50 for details on operation of the Watchdog Timer.

TOUT

ATmega128(L)

2467B–09/01

Figure 26. Watchdog Reset During Operation

ATmega128(L)

MCU Control and Status Register – MCUCSR

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

Bit 76543210

JTD - - JTRF WDRF BORF EXTRF PORF MCUCSR

Read/Write R/W R R R/W R/W R/W R/W R/W

Initial value 0 0 0 See bit description

Note that only EXTRF and PORF are available in ATmega103 compatibility mode.

• Bit 4 - JTRF: JTAG Reset Flag

This bit is set if a reset is being caused by a logic one in the JTAG Reset Register selected by the JTAG instruction AVR_RESET. This bit is reset by a Power-on reset, or by writing a logic zero to the flag.

• Bit 3 - WDRF: Watchdog Reset Flag

This bit is set if a watchdog reset occurs. The bit is reset by a power-on reset, or by writing a logic zero to the flag.

• Bit 2 - BORF: Brown-out Reset Flag

This bit is set if a brown-out reset occurs. The bit is reset by a power-on reset, or by writing a logic zero to the flag.

• Bit 1 - EXTRF: External Reset Flag

This bit is set if an external reset occurs. The bit is reset by a power-on reset, or by writing a logic zero to the flag.

• Bit 0 - PORF: Power-On Reset Flag

Internal Voltage Reference

2467B–09/01

This bit is set if a power-on reset occurs. The bit is reset only by writing a logic zero to the flag.

To make use of the reset flags to identify a reset condition, the user should read and then reset the MCUCSR as early as possible in the program. If the register is cleared before another reset occurs, the source of the reset can be found by examining the reset flags.

ATmega128 features an internal bandgap reference. This reference is used for Brownout Detection, and it can be used as an input to the Analog Comparator or the ADC. The

2.56V reference to the ADC is generated from the internal bandgap reference.

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 20. 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 BODEN 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.

Thus, when the BOD is not enabled, after setting the ACBG bit or enabling the ADC, the user must always allow the reference to start up before the output from the Analog Comparator or ADC 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.

Table 20. Internal Voltage Reference Characteristics

Symbol Parameter Condition Min Typ Max Units

Note: 1. Values are guidelines only. Actual values are TBD.

Bandgap reference voltage TBD TBD 1.23 TBD V

Bandgap reference start-up time TBD 40 70 µs

Bandgap reference current consumption

(1)

TBD 10 TBD µA

Watchdog Timer The Watchdog Timer is clocked from a separate on-chip oscillator which runs at 1 Mhz.

This is the typical value at V

levels. By controlling the Watchdog Timer prescaler, the Watchdog reset interval

can be adjusted as shown in instruction resets the Watchdog Timer. The Watchdog Timer is also reset when it is disabled and when a chip reset occurs. Eight different clock cycle periods can be selected to determine the reset period. If the reset period expires without another Watchdog reset, the ATmega128 resets and executes from the Reset vector. For timing details on the Watchdog reset, refer to

To prevent unintentional disabling of the watchdog or unintentional change of time-out period, 3 different safety levels are selected by the Fuses M103C and WDTON as shown in Table 21. Safety level 0 corresponds to the setting in ATmega103. There is no restriction on enabling the WDT in any of the safety levels. Refer to

for Changing the Configuration of the Watch Dog Timer” on page 53

= 5V. See characterization data for typical values at other

Table 22 on page 52. The WDR – Watchdog Reset –

page 48.

“Timed Sequences

for details.

ATmega128(L)

2467B–09/01

ATmega128(L)

Table 2 1. WDT Configuration as a Function of the Fuse Settings of M103C and

WDTON.

How to

M103C WDTON

Safety Level

WDT Initial State

How to Disable the WDT

Change Time-out

Unprogrammed Unprogrammed 1 Disabled Timed

sequence

Unprogrammed Programmed 2 Enabled Always enabled Timed

Programmed Unprogrammed 0 Disabled Timed

sequence

Programmed Programmed 2 Enabled Always enabled Timed

Timed sequence

sequence

No restriction

sequence

Figure 27. Watchdog Timer

WATCHDOG

OSCILLATOR

Watchdog Timer Control Register – WDTCR

2467B–09/01

Bit 76543210

–––WDCE WDE WDP2 WDP1 WDP0 WDTCR

Read/Write R R R R/W R/W R/W R/W R/W

Initial value00000000

• Bits 7..5 - Res: Reserved Bits

These bits are reserved bits in the ATmega128 and will always read as zero.

• Bit 4 - WDCE: Watchdog Change Enable

This bit must be set when the WDE bit is written to logic zero. Otherwise, the watchdog will not be disabled. Once written to one, hardware will clear this bit after four clock cycles. Refer to the description of the WDE bit for a watchdog disable procedure. In Safety Level 1 and 2, this bit must also be set when changing the prescaler bits.

See

“Timed Sequences for Changing the Configuration of the Watch Dog Timer” on page 53.

• Bit 3 - WDE: Watchdog Enable

When the WDE is written to logic one, the Watchdog Timer is enabled, and if the WDE is written to logic zero, the Watchdog Timer function is disabled. WDE can only be cleared if the WDCE bit has logic level one. To disable an enabled watchdog timer, the following procedure must be followed:

1. In the same operation, write a logic one to WDCE and WDE. A logic one must be written to WDE even though it is set to one before the disable operation starts.

2. Within the next four clock cycles, write a logic 0 to WDE. This disables the watchdog.

In safety level 2, it is not possible to disable the Watchdog Timer, even with the algorithm described above.

See “Timed Sequences for Changing the Configuration of the

Watch Dog Timer” on page 53.

• Bits 2..0 - WDP2, WDP1, WDP0: Watchdog Timer Prescaler 2, 1, and 0

The WDP2, WDP1, and WDP0 bits determine the Watchdog Timer prescaling when the Watchdog Timer is enabled. The different prescaling values and their corresponding Timeout Periods are shown in

Table 22. Watchdog Timer Prescale Select

Table 22.

(1)

Number of WDT

WDP2 WDP1 WDP0

000 16K TBD 16 ms

001 32K TBD 32 ms

010 64K TBD 64 ms

0 1 1 128K TBD 0.13 s

1 0 0 256K TBD 0.26 s

1 0 1 512K TBD 0.5 s

1 1 0 1,024K TBD 1.0 s

1 1 1 2,048K TBD 2.0 s

Note: 1. Values are guidelines only. Actual values are TBD.

Oscillator Cycles

Typical Time-out

at VCC = 3.0V

Typical Time-out

at VCC = 5.0V

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

Assembly Code Example

WDT_off:

; Write logical one to WDCE and WDE

ldi r16, (1<<WDCE)|(1<<WDE)

out WDTCR, r16

; Turn off WDT

ldi r16, (0<<WDE)

out WDTCR, r16

ret

C Code Example

void WDT_off(void)

{

/* Write logical one to WDCE and WDE */

WDTCR = (1<<WDCE) | (1<<WDE);

/* Turn off WDT */

WDTCR = 0x00;

}

ATmega128(L)

2467B–09/01

ATmega128(L)

Timed Sequences for Changing the

The sequence for changing configuration differs slightly between the 3 safety levels. Separate procedures are described for each level.

Configuration of the Watch Dog Timer

Safety Level 0 This mode is compatible with the watchdog operation found in ATmega103. The watch-

dog timer is initially disabled, but can be enabled by writing the WDE bit to 1 without any restriction. The time-out period can be changed at any time without restriction. To disable an enabled watchdog timer, the procedure described on description) must be followed.

Safety Level 1 In this mode, the watchdog timer is initially disabled, but can be enabled by writing the

WDE bit to 1 without any restriction. A timed sequence is needed when changing the watchdog time-out period or disabling an enabled watch dog timer. To disable an enabled watchdog timer, and/or changing the watch dog time-out, the following procedure must be followed:

1. In the same operation, write a logic one to WDCE and WDE. A logic one must be written to WDE regardless of the previous value of the WDE bit.

2. Within the next four clock cycles, in the same operation, write the WDE and WDP bits as desired, but with the WDCE bit cleared.

Safety Level 2 In this mode, the watchdog timer is always enabled, and the WDE bit will always read as

one. A timed sequence is needed when changing the watchdog time-out period. To change the watch dog time-out, the following procedure must be followed:

1. In the same operation, write a logical one to WDCE and WDE. Even though the WDE always is set, the WDE must be written to one to start the timed sequence.

2. Within the next four clock cycles, in the same operation, write the WDP bits as desired, but with the WDCE bit cleared. The value written to the WDE bit is irrelevant.

page 51 (WDE bit

2467B–09/01

Interrupts This chapter describes the specifics of the interrupt handling as performed in

“Reset

Interrupt Vectors in ATm eg a1 28

ATmega128. For a general explanation of the AVR interrupt handling, refer to

and Interrupt Handling” on page 13

Table 23. Reset and Interrupt Vectors

Vector

No.

1 $0000

2 $0002 INT0 External Interrupt Request 0

3 $0004 INT1 External Interrupt Request 1

4 $0006 INT2 External Interrupt Request 2

5 $0008 INT3 External Interrupt Request 3

6 $000A INT4 External Interrupt Request 4

7 $000C INT5 External Interrupt Request 5

8 $000E INT6 External Interrupt Request 6

9 $0010 INT7 External Interrupt Request 7

10 $0012 TIMER2 COMP Timer/Counter2 Compare Match

11 $0014 TIMER2 OVF Timer/Counter2 Overflow

12 $0016 TIMER1 CAPT Timer/Counter1 Capture Event

13 $0018 TIMER1 COMPA Timer/Counter1 Compare Match A

14 $001A TIMER1 COMPB Timer/Counter1 Compare Match B

15 $001C TIMER1 OVF Timer/Counter1 Overflow

Program

Address

(2)

Source Interrupt Definition

(1)

RESET

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

ATmega128(L)

16 $001E TIMER0 COMP Timer/Counter0 Compare Match

17 $0020 TIMER0 OVF Timer/Counter0 Overflow

18 $0022 SPI, STC SPI Serial Transfer Complete

19 $0024 USART0, RX USART0, Rx Complete

20 $0026 USART0, UDRE USART0 Data Register Empty

21 $0028 USART0, TX USART0, Tx Complete

22 $002A ADC ADC Conversion Complete

23 $002C EE READY EEPROM Ready

24 $002E ANALOG COMP Analog Comparator

25 $0030

26 $0032

27 $0034

28 $0036

29 $0038

30 $003A

(3)

TIMER1 COMPC Timer/Countre1 Compare Match C

(3)

TIMER3 CAPT Timer/Counter3 Capture Event

(3)

TIMER3 COMPA Timer/Counter3 Compare Match A

(3)

TIMER3 COMPB Timer/Counter3 Compare Match B

(3)

TIMER3 COMPC Timer/Counter3 Compare Match C

(3)

TIMER3 OVF Timer/Counter3 Overflow

2467B–09/01

Table 23. Reset and Interrupt Vectors (Continued)

ATmega128(L)

Vector

No.

31 $003C

32 $003E

33 $0040

34 $0042

35 $0044

Program

Address

(2)

Source Interrupt Definition

(3)

USART1, RX USART1, Rx Complete

(3)

USART1, UDRE USART1 Data Register Empty

(3)

USART1, TX USART1, Tx Complete

(3)

TWI 2-wire Serial Interface

(3)

SPM READY Store Program Memory Ready

Notes: 1. When the BOOTRST fuse is programmed, the device will jump to the Boot Loader

address at reset, see “Boot Loader Support – Read-While-Write Self-Programming” on page 266.

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 address in this table added to the start address of the boot Flash section.

3. The Interrupts on address $0030 - $0044 do not exist in ATmega103 compatibility mode.

Table 24 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 24. Reset and Interrupt Vectors Placement

BOOTRST IVSEL Reset address Interrupt Vectors Start Address

1 0 $0000 $0002

1 1 $0000 Boot Reset Address + $0002

0 0 Boot Reset Address $0002

0 1 Boot Reset Address Boot Reset Address + $0002

Note: The Boot Reset Address is shown in Table 113 on page 277. For the BOOTRST fuse “1”

means unprogrammed while “0” means programmed.

2467B–09/01

The most typical and general program setup for the Reset and Interrupt Vector Addresses in ATmega128 is:

Address Labels Code Comments

$0000 jmp RESET ; Reset Handler

$0002 jmp EXT_INT0 ; IRQ0 Handler

$0004 jmp EXT_INT1 ; IRQ1 Handler

$0006 jmp EXT_INT2 ; IRQ2 Handler

$0008 jmp EXT_INT3 ; IRQ3 Handler

$000A jmp EXT_INT4 ; IRQ4 Handler

$000C jmp EXT_INT5 ; IRQ5 Handler

$000E jmp EXT_INT6 ; IRQ6 Handler

$0010 jmp EXT_INT7 ; IRQ7 Handler

$0012 jmp TIM2_COMP ; Timer2 Compare Handler

$0014 jmp TIM2_OVF ; Timer2 Overflow Handler

$0016 jmp TIM1_CAPT ; Timer1 Capture Handler

$0018 jmp TIM1_COMPA ; Timer1 CompareA Handler

$001A jmp TIM1_COMPB ; Timer1 CompareB Handler

$001C jmp TIM1_OVF ; Timer1 Overflow Handler

$001E jmp TIM0_COMP ; Timer0 Compare Handler

$0020 jmp TIM0_OVF ; Timer0 Overflow Handler

$0022 jmp SPI_STC ; SPI Transfer Complete Handler

$0024 jmp USART0_RXC ; USART0 RX Complete Handler

$0026 jmp USART0_DRE ; USART0,UDR Empty Handler

$0028 jmp USART0_TXC ; USART0 TX Complete Handler

$002A jmp ADC ; ADC Conversion Complete Handler

$002C jmp EE_RDY ; EEPROM Ready Handler

$002E jmp ANA_COMP ; Analog Comparator Handler

$0030 jmp TIM1_COMPC ; Timer1 CompareC Handler

$0032 jmp TIM3_CAPT ; Timer3 Capture Handler

$0034 jmp TIM3_COMPA ; Timer3 CompareA Handler

$0036 jmp TIM3_COMPB ; Timer3 CompareB Handler

$0038 jmp TIM3_COMPC ; Timer3 CompareC Handler

$003A jmp TIM3_OVF ; Timer3 Overflow Handler

$003C jmp USART1_RXC ; USART1 RX Complete Handler

$003E jmp USART1_DRE; USART1,UDR Empty Handler

$0040 jmp USART1_TXC ; USART1 TX Complete Handler

$0042 jmp TWI ; 2-wire Serial Interface Interrupt Handler

$0044 jmp SPM_RDY ; SPM Ready Handler

;

$0046 RESET:ldir16, high(RAMEND); Main program start

$0047 out SPH,r16 ; Set stack pointer to top of RAM

$0048 ldi r16, low(RAMEND)

$0049 out SPL,r16 $004A sei ; Enable interrupts

$004B <instr> xxx

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

ATmega128(L)

2467B–09/01

ATmega128(L)

When the BOOTRST fuse is unprogrammed, the boot section size set to 8K 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 is:

Address Labels Code Comments

$0000 RESET:ldi r16,high(RAMEND) ; Main program start

$0001 out SPH,r16 ; Set stack pointer to top of RAM

$0002 ldi r16,low(RAMEND)

$0003 out SPL,r16 $0004 sei ; Enable interrupts

$0005 <instr> xxx

;

.org $F002

$F002 jmp EXT_INT0 ; IRQ0 Handler

$F004 jmp EXT_INT1 ; IRQ1 Handler

... ... ... ;

$F044 jmp SPM_RDY ; Store Program Memory Ready Handler

When the BOOTRST fuse is programmed and the boot section size set to 8K bytes, the most typical and general program setup for the Reset and Interrupt Vector Addresses is:

Address Labels Code Comments

.org $0002

$0002 jmp EXT_INT0 ; IRQ0 Handler

$0004 jmp EXT_INT1 ; IRQ1 Handler

... ... ... ;

$0044 jmp SPM_RDY ; Store Program Memory Ready Handler

;

.org $F000 $F000 RESET: ldi r16,high(RAMEND) ; Main program start

$F001 out SPH,r16 ; Set stack pointer to top of RAM

$F002 ldi r16,low(RAMEND)

$F003 out SPL,r16 $F004 sei ; Enable interrupts

$F005 <instr> xxx

2467B–09/01

When the BOOTRST fuse is programmed, the boot section size set to 8K 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 is:

Address Labels Code Comments

;

.org $F000 $F000 jmp RESET ; Reset handler $F002 jmp EXT_INT0 ; IRQ0 Handler

$F004 jmp EXT_INT1 ; IRQ1 Handler

... ... ... ;

$F044 jmp SPM_RDY ; Store Program Memory Ready Handler

$F046 RESET: ldi r16,high(RAMEND) ; Main program start

$F047 out SPH,r16 ; Set stack pointer to top of RAM

$F048 ldi r16,low(RAMEND)

$F049 out SPL,r16 $F04A sei ; Enable interrupts

$F04B <instr> xxx

Moving Interrupts Between Application and Boot Space

MCU Control Register – MCUCR

The General Interrupt Control Register controls the placement of the interrupt vector table.

Bit 76543210

SRE SRW10 SE SM1 SM0 SM2 IVSEL IVCE MCUCR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial value00000000

• 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

Support – Read-While-Write Self-Programming” on page 266

for details. To avoid unin-

“Boot Loader

tentional changes of interrupt vector tables, a special write procedure must be followed to change the IVSEL bit:

1. Write the Interrupt Vector Change Enable (IVCE) bit to one.

2. Within four cycles, write the desired value to IVSEL while writing a zero to IVCE.

Interrupts will automatically be disabled while this sequence is executed. Interrupts are disabled in the cycle IVCE is set, and they remain disabled until after the instruction following the write to IVSEL. If IVSEL is not written, interrupts remain disabled for four cycles. The I-bit in the Status Register is unaffected by the automatic disabling.

Note: If interrupt vectors are placed in the Boot Loader section and Boot Lock bit BLB02 is programmed, interrupts are disabled while executing from the Application section. If interrupt vectors are placed in the Application section and Boot Lock bit BLB12 is programed, interrupts are disabled while executing from the Boot Loader section. Refer to the section

“Boot Loader Support – Read-While-Write Self-Programming” on page 266

for details on Boot Lock bits.

ATmega128(L)

2467B–09/01

ATmega128(L)

• 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);

}

2467B–09/01

I/O-Ports

Introduction All AVR ports have true Read-Modify-Write functionality when used as general digital

I/O ports. This means that the direction of one port pin can be changed without unintentionally changing the direction of any other pin with the SBI and CBI instructions. The same applies when 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. The pin driver is strong enough to drive LED displays directly. All port pins have individually selectable pull-up resistors with a supply-voltage invariant resistance. All I/O pins have protection diodes to both

and Ground as indicated in Figure 28. Refer to “Electrical Characteristics” on page

310

for a complete list of parameters.

Figure 28. I/O Pin Equivalent Schematic

Pxn

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. I.e. PORTB3 for bit no. 3 in Port B, here documented generally as PORTxn. The physical I/O registers and bit locations are listed in

for I/O Ports” on page 81

Three I/O memory address locations are allocated for each port, one each for the Data Register - PORTx, Data Direction Register – DDRx, and the Port Input Pins – PINx. The Port Input Pins I/O location is read only, while the Data Register and the Data Direction Register are read/write. In addition, the Pull-up Disable – PUD bit in SFIOR disables the pull-up function for all pins in all ports when set.

Using the I/O port as General Digital I/O is described in

page 61

tures on the device. How each alternate function interferes with the port pin is described in full description of the alternate functions.

. Most port pins are multiplexed with alternate functions for the peripheral fea-

“Alternate Port Functions” on page 66. Refer to the individual module sections for a

See Figure

"General Digital I/O" for

“Ports as General Digital I/O” on

Logic

Details

“Register Description

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.

ATmega128(L)

2467B–09/01

ATmega128(L)

Ports as General Digital I/O

The ports are bi-directional I/O ports with optional internal pull-ups. Figure 29 shows a functional description of one I/O port pin, here generically called Pxn.

Figure 29. General Digital I/O

Pxn

(1)

SLEEP

SYNCHRONIZER

DLQ

PINxn

PUD

DDxn

CLR

RESET

PORTxn

CLR

RESET

WDx

RDx

WPx

RRx

RPx

DATA BUS

clk

I/O

PUD: PULLUP DISABLE SLEEP: SLEEP CONTROL clk

: I/O CLOCK

I/O

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

WDx: WRITE DDRx RDx: READ DDRx WPx: WRITE PORTx RRx: READ PORTx REGISTER RPx: READ PORTx PIN

I/O

SLEEP, and PUD are common to all ports.

Configuring the Pin Each port pin consists of 3 Register bits: DDxn, PORTxn, and PINxn. As shown in “Reg-

ister Description for I/O Ports” on page 81

, the DDxn bits are accessed at the DDRx I/O address, the PORTxn bits at the PORTx I/O address, and the PINxn bits at the PINx I/O address.

The DDxn bit in the DDRx register selects the direction of this pin. If DDxn is written logic one, Pxn is configured as an output pin. If DDxn is written logic zero, Pxn is configured as an input pin.

If PORTxn is written logic one when the pin is configured as an input pin, the pull-up resistor is activated. To switch the pull-up resistor off, PORTxn has to be written logic zero or the pin has to be configured as an output pin. The port pins are tri-stated when a reset condition becomes active, even if no clocks are running.

If PORTxn is written logic one when the pin is configured as an output pin, the port pin is driven high (one). If PORTxn is written logic zero when the pin is configured as an output pin, the port pin is driven low (zero).

2467B–09/01

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 SFIOR register can be written to one 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} = 0b10) as an intermediate step.

Table 25 summarizes the control signals for the pin value.

Table 25. Port Pin Configurations

PUD

DDxn PORTxn

0 0 X Input No Tri-state (Hi-Z)

0 1 0 Input Yes

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)

(in SFIOR) I/O Pull-up Comment

Pxn will source current if ext. pulled low.

Reading the Pin Value Independent of the setting of Data Direction bit DDxn, the port pin can be read through

the PINxn Register Bit. As shown in

Figure 29, the PINxn Register bit and the preceding

latch constitute a synchronizer. This is needed to avoid metastability if the physical pin

and t

Figure

pd,min

changes value near the edge of the internal clock, but it also introduces a delay.

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

respectively.

ATmega128(L)

2467B–09/01

ATmega128(L)

Figure 30. Synchronization when Reading an Externally Applied Pin Value

SYSTEM CLK

INSTRUCTIONS

XXXXXX

in r17, PINx

SYNC LATCH

PINxn

pd,min

0xFF

, a single

r17

0x00

pd, max

pd, min

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

pd,max

and t signal transition on the pin will be delayed between ½ and 1½ system clock period depending upon the time of assertion.

2467B–09/01

When reading back a software assigned pin value, a nop instruction must be inserted as indicated in edge of the clock. In this case, the delay t

Figure 31. The out instruction sets the “SYNC LATCH” signal at the positive

through the synchronizer is 1 system clock

period.

Figure 31. Synchronization when Reading a Software Assigned Pin Value

SYSTEM CLK

r16

INSTRUCTIONS

out PORTx, r16

0xFF

nop in r17, PINx

SYNC LATCH

PINxn

r17

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.

0x00

0xFF

ATmega128(L)

2467B–09/01

ATmega128(L)

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

...

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;

...

(1)

Digital Input Enable and Sleep Modes

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.

As shown in Figure 29, the digital input signal can be clamped to ground at the input of the schmitt-trigger. The signal denoted SLEEP in the figure, is set by the MCU Sleep Controller in Power-down mode, Power-save Mode, Standby Mode, and Extended Standby Mode to avoid high power consumption if some input signals are left floating, or have an analog signal level close to V

/2.

SLEEP is overridden for port pins enabled as External Interrupt pins. If the External Interrupt Request is not enabled, SLEEP is active also for these pins. SLEEP is also overridden by various other alternate functions as described in

tions” on page 66

“Alternate Port Func-

If a logic high level (“one”) is present on an Asynchronous External Interrupt pin configured as “Interrupt on 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.

2467B–09/01

Alternate Port Functions Most port pins have alternate functions in addition to being general digital I/Os. Figure

shows how the port pin control signals from the simplified Figure 29 can be overridden by alternate functions. The overriding signals may not be present in all port pins, but the figure serves as a generic description applicable to all port pins in the AVR microcontroller family.

Figure 32. Alternate Port Functions

Pxn

(1)

PUOExn

PUOVxn

DDOExn

DDOVxn

PVOExn

PVOVxn

DIEOExn

DIEOVxn

SLEEP

SYNCHRONIZER

SET

DLQ

CLR

PINxn

PUD

DDxn

CLR

RESET

PORTxn

CLR

RESET

CLR

clk

WDx

RDx

WPx

RRx

RPx

DATA BUS

I/O

DIxn

AIOxn

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

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

PUD: PULLUP DISABLE WDx: WRITE DDRx RDx: READ DDRx RRx: READ PORTx REGISTER WPx: WRITE PORTx RPx: READ PORTx PIN

: I/O CLOCK

clk

I/O

DIxn: DIGITAL INPUT PIN n ON PORTx AIOxn: ANALOG INPUT/OUTPUT PIN n ON PORTx

I/O

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

Table 26 summarizes the function of the overriding signals. The pin and port indexes

Figure 32 are not shown in the succeeding tables. The overriding signals are gen-

from erated internally in the modules having the alternate function.

ATmega128(L)

2467B–09/01

ATmega128(L)

Table 26. Generic Description of Overriding Signals for Alternate Functions.

Signal Name Full Name Description

PUOE Pull-up

Override Enable

PUOV Pull-up

Override Value

DDOE Data Direction

Override Enable

DDOV Data Direction

Override Value

PVOE Port Value

Override Enable

PVOV Port Value

Override Value

DIEOE Digital Input

Enable Override Enable

DIEOV Digital Input

Enable Override Val ue

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 this bit is set, the Digital Input Enable is controlled by the DIEOV signal. If this signal is cleared, the Digital Input Enable is determined by MCU-state (Normal Mode, Sleep Modes).

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

Special Function IO Register – SFIOR

2467B–09/01

DI Digital Input This is the Digital Input to alternate functions. In the

figure, the signal is connected to the output of the schmitt trigger but before the synchronizer. Unless the Digital Input is used as a clock source, the module with the alternate function will use its own synchronizer.

AIO Analog

Input/output

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

The following subsections shortly describes the alternate functions for each port, and relates the overriding signals to the alternate function. Refer to the alternate function description for further details.

Bit 7 6 5 4 3 2 1 0

TSM – – ADHSM ACME PUD PSR0 PSR321 SFIOR

Read/Write R/W R R R/W R/W R/W R/W R/W

Initial value 0 0 0 0 0 0 0 0

• Bit 2 - PUD: Pull-up disable

When this bit is written to one, the pull-ups in the I/O ports are disabled even if the DDxn and PORTxn registers are configured to enable the pull-ups ({DDxn, PORTxn} = 0b01).

“Configuring the Pin” on page 61 for more details about this feature.

See

Alternate Functions of Port A The Port A has an alternate function as the address low byte and data lines for the

External Memory Interface.

Table 27. Port A Pins Alternate Functions

Port Pin Alternate Function

PA7 AD7 (External memory interface address and data bit 7)

PA6 AD6 (External memory interface address and data bit 6)

PA5 AD5 (External memory interface address and data bit 5)

PA4 AD4 (External memory interface address and data bit 4)

PA3 AD3 (External memory interface address and data bit 3)

PA2 AD2 (External memory interface address and data bit 2)

PA1 AD1 (External memory interface address and data bit 1)

PA0 AD0 (External memory interface address and data bit 0)

Table 28 and Table 29 relates the alternate functions of Port A to the overriding signals

shown in

Figure 32 on page 66.

Table 28. Overriding Signals for Alternate Functions in PA7..PA4

Signal Name PA7/AD7 PA6/AD6 PA5/AD5 PA4/AD4

PUOE SRE SRE SRE SRE

PUOV ~(WR | ADA

PORTA7 • PUD

DDOE SRE SRE SRE SRE

DDOV WR | ADA WR | ADA WR | ADA WR | ADA

PVOE SRE SRE SRE SRE

PVOV A7 • ADA | D7

OUTPUT • WR

DIEOE0000

DIEOV0000

DID7 INPUTD6 INPUTD5 INPUTD4 INPUT

AIO ––––

Note: 1. ADA is short for ADdress Active and represents the time when address is output. See

“External Memory Interface” on page 24 for details.

(1)

) •

~(WR | ADA) • PORTA6 • PUD

A6 • ADA | D6 OUTPUT • WR

~(WR | ADA) • PORTA5 • PUD

A5 • ADA | D5 OUTPUT • WR

~(WR | ADA) • PORTA4 • PUD

A4 • ADA | D4 OUTPUT • WR

ATmega128(L)

2467B–09/01

ATmega128(L)

Table 29. Overriding Signals for Alternate Functions in PA3..PA0

Signal Name PA3/AD3 PA2/AD2 PA1/AD1 PA0/AD0

PUOE SRE SRE SRE SRE

PUOV ~(WR

DDOE SRE SRE SRE SRE

DDOV WR

PVOE SRE SRE SRE SRE

PVOV A3 • ADA | D3

DIEOE0000

DIEOV0000

DI D3 INPUT D2 INPUT D1 INPUT D0 INPUT

AIO ––––

| ADA) •

PORTA3 • PUD

| ADA WR | ADA WR | ADA WR | ADA

OUTPUT • WR

~(WR | ADA) • PORTA2 • PUD

A2• ADA | D2 OUTPUT • WR

~(WR | ADA) • PORTA1 • PUD

A1 • ADA | D1 OUTPUT • WR

Alternate Functions of Port B The Port B pins with alternate functions are shown in Table 30.

Table 30. Port B Pins Alternate Functions

Port Pin Alternate Functions

PB7

PB6 OC1B (Output Compare and PWM Output B for Timer/Counter1)

PB5 OC1A (Output Compare and PWM Output A for Timer/Counter1)

PB4 OC0 (Output Compare and PWM Output for Timer/Counter0)

OC2/OC1C Compare and PWM Output C for Timer/Counter1)

(1)

(Output Compare and PWM Output for Timer/Counter2 or Output

~(WR | ADA) • PORTA0 • PUD

A0 • ADA | D0 OUTPUT • WR

2467B–09/01

PB3 MISO (SPI Bus Master Input/Slave Output)

PB2 MOSI (SPI Bus Master Output/Slave Input)

PB1 SCK (SPI Bus Serial Clock)

PB0 SS

Note: 1. OC1C not applicable in ATmega103 compatibility mode.

(SPI Slave Select input)

The alternate pin configuration is as follows:

• OC2/OC1C, Bit 7

OC2, Output Compare match output: The PB7 pin can serve as an external output for the Timer/Counter2 output compare. The pin has to be configured as an output (DDB7 set “one”) to serve this function. The OC2 pin is also the output pin for the PWM mode timer function.

OC1C, Output Compare matchC output: The PB7 pin can serve as an external output for the Timer/Counter1 output compareC. The pin has to be configured as an output (DDB7 set (one)) to serve this function. The OC1C pin is also the output pin for the PWM mode timer function.

• OC1B, Bit 6

OC1B, Output Compare matchB output: The PB6 pin can serve as an external output for the Timer/Counter1 output compareB. The pin has to be configured as an output (DDB6 set (one)) to serve this function. The OC1B pin is also the output pin for the PWM mode timer function.

• OC1A, Bit 5

OC1A, Output Compare matchA output: The PB5 pin can serve as an external output for the Timer/Counter1 output compareA. The pin has to be configured as an output (DDB5 set (one)) to serve this function. The OC1A pin is also the output pin for the PWM mode timer function.

• OC0, Bit 4

OC0, Output Compare match output: The PB4 pin can serve as an external output for the Timer/Counter0 output compare. The pin has to be configured as an output (DDB4 set (one)) to serve this function. The OC0 pin is also the output pin for the PWM mode timer function.

• MISO - Port B, Bit 3

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 DDB3. When the SPI is enabled as a slave, the data direction of this pin is controlled by DDB3. When the pin is forced to be an input, the pull-up can still be controlled by the PORTB3 bit.

• MOSI - Port B, Bit 2

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 DDB2. When the SPI is enabled as a master, the data direction of this pin is controlled by DDB2. When the pin is forced to be an input, the pull-up can still be controlled by the PORTB2 bit.

• SCK - Port B, Bit 1

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 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 bit.

- Port B, Bit 0

• SS

: Slave port select input. When the SPI is enabled as a slave, this pin is configured as an input regardless of the setting of DDB0. 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 DDB0. When the pin is forced to be an input, the pull-up can still be controlled by the PORTB0 bit.

Table 31 and Table 32 relate the alternate functions of Port B to the overriding signals

shown in the MISO signal, while MOSI is divided into SPI MSTR OUTPUT and SPI SLAVE INPUT.

Figure 32 on page 66. SPI MSTR INPUT and SPI SLAVE OUTPUT constitute

ATmega128(L)

2467B–09/01

ATmega128(L)

Table 31. Overriding Signals for Alternate Functions in PB7..PB4

Signal Name PB7/OC2/OC1C PB6/OC1B PB5/OC1A PB4/OC0

PUOE0 000

PUOV0 000

DDOE 0 0 0 0

DDOV 0 0 0 0

PVOE OC2/OC1C ENABLE

PVOV OC2/OC1C

(1)

DIEOE0 000

DIEOV0 000

DI – –––

AIO – –––

Note: 1. See “Output Compare Modulator (OCM1C2)” on page 155 for details. OC1C does

not exist in ATmega103 compatibility mode.

(1)

OC1B ENABLE OC1A ENABLE OC0 ENABLE

OC1B OC1A OC0B

Table 32. Overriding Signals for Alternate Functions in PB3..PB0

Signal Name PB3/MISO PB2/MOSI PB1/SCK PB0/SS

PUOE SPE • MSTR SPE • MSTR SPE • MSTR SPE • MSTR

PUOV PORTB3 • PUD PORTB2 • PUD PORTB1 • PUD PORTB0 • PUD

DDOE SPE • MSTR SPE • MSTR SPE • MSTR SPE • MSTR

DDOV 0 0 0 0

PVOE SPE • MSTR

PVOV SPI SLAVE OUTPUT SPI MSTR OUTPUT SCK OUTPUT 0

DIEOE 0 0 0 0

DIEOV 0 0 0 0

DI SPI MSTR INPUT SPI SLAVE INPUT SCK INPUT SPI SS

AIO ––––

SPE • MSTR SPE • MSTR 0

2467B–09/01

Alternate Functions of Port C In ATmega103 compatibility mode, Port C is output only. The Port C has an alternate

function as the address high byte for the External Memory Interface.

Table 33. Port C Pins Alternate Functions

Port Pin Alternate Function

PC7 A15

PC6 A14

PC5 A13

PC4 A12

PC3 A11

PC2 A10

PC1 A9

PC0 A8

Table 34 and Table 35 relate the alternate functions of Port C to the overriding signals

shown in

Figure 32 on page 66.

Table 34. Overriding Signals for Alternate Functions in PC7..PC4

Signal Name PC7/A15 PC6/A14 PC5/A13 PC4/A12

(1)

PUOE SRE • (XMM

<1) SRE • (XMM<2) SRE • (XMM<3) SRE • (XMM<4)

PUOV 0 0 0 0

DDOE SRE • (XMM<1) SRE • (XMM<2) SRE • (XMM<3) SRE • (XMM<4)

DDOV 1 1 1 1

PVOE SRE • (XMM<1) SRE • (XMM<2) SRE • (XMM<3) SRE • (XMM<4)

PVOV A11 A10 A9 A8

DIEOE 0 0 0 0

DIEOV 0 0 0 0

DI ––––

AIO ––––

Note: 1. XMM = 0 in ATmega103 compatibility mode.

ATmega128(L)

2467B–09/01

ATmega128(L)

Table 35. Overriding Signals for Alternate Functions in PC3..PC0

Signal Name PC3/A11 PC2/A10 PC1/A9 PC0/A8

PUOE SRE • (XMM<5) SRE • (XMM<6) SRE • (XMM<7) SRE • (XMM<7)

PUOV0000

DDOE SRE • (XMM<5) SRE • (XMM<6) SRE • (XMM<7) SRE • (XMM<7)

DDOV 1 1 1 1

PVOE SRE • (XMM<5) SRE • (XMM<6) SRE • (XMM<7) SRE • (XMM<7)

PVOV A11 A10 A9 A8

DIEOE0000

DIEOV0000

DI ––––

AIO ––––

Note: 1. XMM = 0 in ATmega103 compatibility mode.

Alternate Functions of Port D The Port D pins with alternate functions are shown in Table 36.

Table 36. Port D Pins Alternate Functions

Port Pin Alternate Function

PD7 T2 (Timer/Counter2 Clock Input)

(1)

PD6 T1 (Timer/Counter1 Clock Input)

PD5 XCK1

PD4 IC1 (Timer/Counter1 Input Capture Trigger)

PD3 INT3/TXD1

PD2 INT2/RXD1

PD1 INT1/SDA

PD0 INT0/SCL

Note: 1. XCK1, TXD1, RXD1, SDA, and SCL not applicable in ATmega103 compatibility

mode.

(1)

(USART1 external clock input/output)

(1)

(External Interrupt3 Input or UART1 Transmit Pin)

(1)

(External Interrupt2 Input or UART1 Receive Pin)

(1)

(External Interrupt1 Input or TWI Serial DAta)

(1)

(External Interrupt0 Input or TWI Serial CLock)

The alternate pin configuration is as follows:

• T2 - Port D, Bit 7

T2, Timer/Counter2 counter source.

• T1 - Port D, Bit 6

T1, Timer/Counter1 counter source.

• XCK1 - Port D, Bit 4

XCK1, USART1 external clock. The Data Direction Register (DDD4) controls whether the clock is output (DDD4 set) or input (DDD4 cleared). The XCK1 pin is active only when the USART1 operates in synchronous mode.

2467B–09/01

• IC1 - Port D, Bit 4

IC1 - Input Capture Pin1: The PD4 pin can act as an input capture pin for Timer/Counter1.

• INT3/TXD1 - Port D, Bit 3

INT3, External Interrupt source 3: The PD3 pin can serve as an external interrupt source to the MCU.

TXD1, Transmit Data (Data output pin for the USART1). When the USART1 transmitter is enabled, this pin is configured as an output regardless of the value of DDD3.

• INT2/RXD1 - Port D, Bit 2

INT2, External Interrupt source 2. The PD2 pin can serve as an external interrupt source to the MCU.

RXD1, Receive Data (Data input pin for the USART1). When the USART1 receiver is enabled this pin is configured as an input regardless of the value of DDD2. When the USART forces this pin to be an input, the pull-up can still be controlled by the PORTD2 bit.

• INT1/SDA - Port D, Bit 1

INT1, External Interrupt source 1. The PD1 pin can serve as an external interrupt source to the MCU.

SDA, 2-wire Serial Interface Data: When the TWEN bit in TWCR is set (one) to enable the 2-wire Serial Interface, pin PD1 is disconnected from the port and becomes the Serial Data I/O pin for the 2-wire Serial Interface. In this mode, there is a spike filter on the pin to suppress spikes shorter than 50 ns on the input signal, and the pin is driven by an open drain driver with slew-rate limitation.

• INT0/SCL - Port D, Bit 0

INT0, External Interrupt source 0. The PD0 pin can serve as an external interrupt source to the MCU.

SCL, 2-wire Serial Interface Clock: When the TWEN bit in TWCR is set (one) to enable the 2-wire Serial Interface, pin PD0 is disconnected from the port and becomes the Serial Clock I/O pin for the 2-wire Serial Interface. In this mode, there is a spike filter on the pin to suppress spikes shorter than 50 ns on the input signal, and the pin is driven by an open drain driver with slew-rate limitation.

Table 37 and Table 38 relates the alternate functions of Port D to the overriding signals

shown in

Figure 32 on page 66.

ATmega128(L)

2467B–09/01

ATmega128(L)

Table 37. Overriding Signals for Alternate Functions PD7..PD4

Signal Name PD7/T2 PD6/T1 PD5/XCK1 PD4/IC1

PUOE000 0

PUOV000 0

DDOE 0 0 0 0

DDOV 0 0 0 0

PVOE 0 0 UMSEL1 0

PVOV 0 0 XCK1 OUTPUT 0

DIEOE000 0

DIEOV000 0

DI T2 INPUT T1 INPUT XCK1 INPUT IC1 INPUT

AIO ––– –

Table 38. Overriding Signals for Alternate Functions in PD3..PD0

(1)

Signal Name PD3/INT3/TXD1 PD2/INT2/RXD1 PD1/INT1/SDA PD0/INT0/SCL

PUOE TXEN1 RXEN1 TWEN TWEN

PUOV 0 PORTD2 • PUD

DDOE TXEN1 RXEN1 TWEN TWEN

DDOV 1 0 SDA_OUT SCL_OUT

PVOE TXEN1 0 TWEN TWEN

PVOV TXD1 0 0 0

DIEOE INT3 ENABLE INT2 ENABLE INT1 ENABLE INT0 ENABLE

DIEOV 1 1 1 1

DI INT3 INPUT INT2 INPUT/RXD1 INT1 INPUT INT0 INPUT

AIO –– SDA INPUT SCL INPUT

Note: 1. When enabled, the Two-wire Serial Interface enables Slew-Rate controls on the out-

put pins PD0 and PD1. This is not shown in this table. In addition, spike filters are connected between the AIO outputs shown in the port figure and the digital logic of the TWI module.

PORTD1 • PUD PORTD0 • PUD

2467B–09/01

Alternate Functions of Port E The Port E pins with alternate functions are shown in Table 39.

Table 39. Port E Pins Alternate Functions

Port Pin Alternate Function

PE7 INT7/IC3

PE6 INT6/ T3

PE5

PE4

PE3

PE2

PE1 PDO/TXD0 (Programming Data Output or UART0 Transmit Pin)

PE0 PDI/RXD0 (Programming Data Input or UART0 Receive Pin)

Note: 1. IC3, T3, OC3C, OC3B, OC3B, OC3A, and XCK0 not applicable in ATmega103 com-

INT5/OC3C Timer/Counter3)

INT4/OC3B Timer/Counter3)

AIN1/OC3A Output A for Timer/Counter3)

AIN0/XCK0 input/output)

patibility mode.

(1)

(External Interrupt7 Input or Timer/Counter3 Input Capture Trigger)

(1)

(External Interrupt6 Input or Timer/Counter3 Clock Input)

(1)

(External Interrupt5 Input or Output Compare and PWM Output C for

(1)

(External Interrupt4 Input or Output Compare and PWM Output B for

(1)

(Analog Comparator Negative Input or Output Compare and PWM

(1)

(Analog Comparator Positive Input or USART0 external clock

• INT7/IC3 - Port E, Bit 7

INT7, External Interrupt source 7: The PE7 pin can serve as an external interrupt source.

IC3 - Input Capture Pin3: The PE7 pin can act as an input capture pin for Timer/Counter3.

• INT6/T3 - Port E, Bit 6

INT6, External Interrupt source 6: The PE6 pin can serve as an external interrupt source.

T3, Timer/Counter3 counter source.

• INT5/OC3C - Port E, Bit 5

INT5, External Interrupt source 5: The PE5 pin can serve as an external interrupt source.

OC3C, Output Compare matchC output: The PE5 pin can serve as an external output for the Timer/Counter3 output compareC. The pin has to be configured as an output (DDE5 set “one”) to serve this function. The OC3C pin is also the output pin for the PWM mode timer function.

• INT4/OC3B - Port E, Bit 4

INT4, External Interrupt source 4: The PE4 pin can serve as an external interrupt source.

OC3B, Output Compare matchB output: The PE4 pin can serve as an external output for the Timer/Counter3 output compareB. The pin has to be configured as an output (DDE4 set (one)) to serve this function. The OC3B pin is also the output pin for the PWM mode timer function.

• AIN1/OC3A - Port E, Bit 3

AIN1 - Analog Comparator Negative Input. This pin is directly connected to the negative input of the analog comparator.

ATmega128(L)

2467B–09/01

ATmega128(L)

OC3A, Output Compare matchA output: The PE3 pin can serve as an external output for the Timer/Counter3 output compareA. The pin has to be configured as an output (DDE3 set “one”) to serve this function. The OC3A pin is also the output pin for the PWM mode timer function.

• AIN0/XCK0 - Port E, Bit 2

AIN0 - Analog Comparator Positive Input. This pin is directly connected to the positive input of the analog comparator.

XCK0, USART0 external clock. The Data Direction Register (DDE2) controls whether the clock is output (DDE2 set) or input (DDE2 cleared). The XCK0 pin is active only when the USART0 operates in synchronous mode.

• PDO/TXD0 - Port E, Bit 1

PDO, Serial Programming Data Output. During Serial Program Downloading, this pin is used as data output line for the ATmega128.

TXD0, UART0 Transmit Pin.

• PDI/RXD0 - Port E, Bit 0

PDI, Serial Programming Data Input. During Serial Program Downloading, this pin is used as data input line for the ATmega128.

RXD0, USART0 Receive Pin. Receive Data (Data input pin for the USART0). When the USART0 receiver is enabled this pin is configured as an input regardless of the value of DDRE0. When the USART0 forces this pin to be an input, a logical one in PORTE0 will turn on the internal pull-up.

Table 40 and Table 41 relates the alternate functions of Port E to the overriding signals

shown in

Figure 32 on page 66.

Table 40. Overriding Signals for Alternate Functions PE7..PE4

Signal Name PE7/INT7/IC3 PE6/INT6/T3 PE5/INT5/OC3C PE4/INT4/OC3B

PUOE 0 0 0 0

PUOV 0 0 0 0

DDOE 0 0 0 0

DDOV 0 0 0 0

PVOE 0 0 OC3C ENABLE OC3B ENABLE

PVOV 0 0 OC3C OC3B

DIEOE INT7 ENABLE INT6 ENABLE INT5 ENABLE INT4 ENABLE

DIEOV 1 1 1 1

DI INT7 INPUT/IC3

INPUT

INT7 INPUT/T3 INPUT

INT5 INPUT INT4 INPUT

2467B–09/01

AIO ––––

Table 41. Overriding Signals for Alternate Functions in PE3..PE0

Signal Name PE3/AIN1/OC3A PE2/AIN0/XCK0 PE1/PDO/TXD0 PE0/PDI/RXD0

PUOE 0 0 TXEN0 RXEN0

PUOV 0 0 0 PORTE0 • PUD

DDOE 0 0 TXEN0 RXEN0

DDOV 0 0 1 0

PVOE OC3B ENABLE UMSEL0 TXEN0 0

PVOV OC3B XCK0 OUTPUT TXD0 0

DIEOE 0 0 0 0

DIEOV 0 0 0 0

DI 0 XCK0 INPUT – RXD0

AIO AIN1 INPUT AIN0 INPUT ––

Alternate Functions of Port F The Port F has an alternate function as analog input for the ADC as shown in Table 42.

If some Port F pins are configured as outputs, it is essential that these do not switch when a conversion is in progress. This might corrupt the result of the conversion. In ATmega103 compatibility mode Port F is input only. If the JTAG interface is enabled, the pull-up resistors on pins PF7(TDI), PF5(TMS) and PF4(TCK) will be activated even if a reset occurs.

Table 42. Port F Pins Alternate Functions

Port Pin Alternate Function

PF7 ADC7/TDI (ADC input channel 7 or JTAG Test Data Input)

PF6 ADC6/TDO (ADC input channel 6 or JTAG Test Data Output)

PF5 ADC5/TMS (ADC input channel 5 or JTAG Test Mode Select)

PF4 ADC4/TCK (ADC input channel 4 or JTAG Test ClocK)

PF3 ADC3 (ADC input channel 3)

PF2 ADC2 (ADC input channel 2)

PF1 ADC1 (ADC input channel 1)

PF0 ADC0 (ADC input channel 0)

• TDI, ADC7 - Port F, Bit 7

ADC7, Analog to Digital Converter, Channel 7

TDI, JTAG Test Data In: Serial input data to be shifted in to the Instruction Register or Data Register (scan chains). When the JTAG interface is enabled, this pin can not be used as an I/O pin.

• TCK, ADC6 - Port F, Bit 6

ADC6, Analog to Digital Converter, Channel 6

TDO, JTAG Test Data Out: Serial output data from Instruction register or Data Register. When the JTAG interface is enabled, this pin can not be used as an I/O pin.

ATmega128(L)

2467B–09/01

• TMS, ADC5 - Port F, Bit 5

ATmega128(L)

ADC5, Analog to Digital Converter, Channel 5

TMS, JTAG Test Mode Select: This pin is used for navigating through the TAP-controller state machine. When the JTAG interface is enabled, this pin can not be used as an I/O pin.

• TDO, ADC4 - Port F, Bit 4

ADC4, Analog to Digital Converter, Channel 4

TCK, JTAG Test Clock: JTAG operation is synchronous to TCK. When the JTAG interface is enabled, this pin can not be used as an I/O pin.

• ADC3 - ADC0 - Port F, Bit 3..0

Analog to Digital Converter, Channel 3..0.

Table 43. Overriding Signals for Alternate Functions in PF7..PF4

Signal Name PF7/ADC7/TDI PF6/ADC6/TDO PF5/ADC5/TMS PF4/ADC4/TCK

PUOE JTAGEN JTAGEN JTAGEN JTAGEN

PUOV 1 0 1 1

D DO E J TAG E N J TA GE N J TAG E N J TA GE N

DDOV 0 SHIFT_IR +

SHIFT_DR

PVOE 0 JTAGEN 0 0

PVOV 0 TDO 0 0

D IE OE J TAG E N J TAG E N J TA GE N J TAG E N

DIEOV 0 0 0 0

DI –– – –

AIO TDI/ADC7 INPUT ADC6 INPUT TMS/ADC5

INPUT

TCKADC4 INPUT

Table 44. Overriding Signals for Alternate Functions in PF3..PF0

Signal Name PF3/ADC3 PF2/ADC2 PF1/ADC1 PF0/ADC0

PUOE0000

PUOV0000

DDOE0000

DDOV0000

PVOE0000

PVOV0000

DIEOE0000

DIEOV0000

DI ––––

AIO ADC3 INPUT ADC2 INPUT ADC1 INPUT ADC0 INPUT

2467B–09/01

Alternate Functions of Port G In ATmega103 compatibility mode, only the alternate functions are the defaults for Port

G, and Port G cannot be used as General Digital Port Pins. The alternate pin configuration is as follows:

Table 45. Port G Pins Alternate Functions

Port Pin Alternate Function

PG4 TOSC1 (RTC oscillator Timer/Counter 0)

PG3 TOSC2 (RTC oscillator Timer/Counter 0)

PG2 ALE (Address Latch Enable to external memory)

PG1 RD

PG0 WR

(Read strobe to external memory)

(Write strobe to external memory)

• TOSC1 - Port G, Bit 4

TOSC2, Timer Oscillator pin 1: When the AS0 bit in ASSR is set (one) to enable asynchronous clocking of Timer/Counter0, pin PG4 is disconnected from the port, and becomes the inverting output of the oscillator amplifier. In this mode, a crystal oscillator is connected to this pin, and the pin can not be used as an I/O pin.

• TOSC2 - Port G, Bit 3

TOSC2, Timer Oscillator pin 2: When the AS0 bit in ASSR is set (one) to enable asynchronous clocking of Timer/Counter0, pin PG3 is disconnected from the port, and becomes the input of the inverting oscillator amplifier. In this mode, a crystal oscillator is connected to this pin, and the pin can not be used as an I/O pin.

• ALE - Port G, Bit 2

ALE is the external data memory Address Latch Enable signal.

- Port G, Bit 1

• RD

is the external data memory read control strobe.

• WR - Port G, Bit 0

is the external data memory write control strobe.

Table 46 and Table 47 relates the alternate functions of Port G to the overriding signals

shown in

Figure 32 on page 66.

Table 46. Overriding Signals for Alternate Functions in PG4..PG1

Signal Name PG4/TOSC1 PG3/TOSC2 PG2/ALE PG1/RD

PUOE AS0 AS0 SRE SRE

PUOV 0 0 0 0

DDOE AS0 AS0 SRE SRE

DDOV 0 0 1 1

PVOE 0 0 SRE SRE

PVOV 0 0 ALE RD

DIEOE AS0 AS0 0 0

DIEOV 0 0 0 0

DI –– ––

AIO T/C0 OSC INPUT T/C0 OSC OUTPUT ––

ATmega128(L)

2467B–09/01

Register Description for I/O Ports

ATmega128(L)

Table 47. Overriding Signals for Alternate Functions in PG0

Signal Name PG0/WR

PUOE SRE

PUOV 0

DDOE SRE

DDOV 1

PVOE SRE

PVOV WR

DIEOE 0

DIEOV 0

DI -

AIO -

Port A Data Register – PORTA

Port A Data Direction Register – DDRA

Port A Input Pins Address – PINA

Port B Data Register – PORTB

Port B Data Direction Register – DDRB

Bit 76543210

PORTA7 PORTA6 PORTA5 PORTA4 PORTA3 PORTA2 PORTA1 PORTA0 PORTA

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial value 0 0 0 0 0 0 0 0

Bit 76543210

DDA7 DDA6 DDA5 DDA4 DDA3 DDA2 DDA1 DDA0 DDRA

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial value 0 0 0 0 0 0 0 0

Bit 76543210

PINA7 PINA6 PINA5 PINA4 PINA3 PINA2 PINA1 PINA0 PINA

Read/WriteRRRRRRRR

Initial value N/A N/A N/A N/A N/A N/A N/A N/A

Bit 76543210

PORTB7 PORTB6 PORTB5 PORTB4 PORTB3 PORTB2 PORTB1 PORTB0 PORTB

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial value 0 0 0 0 0 0 0 0

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 value 0 0 0 0 0 0 0 0

2467B–09/01

Port B Input Pins Address – PINB

Bit 76543210

PINB7 PINB6 PINB5 PINB4 PINB3 PINB2 PINB1 PINB0 PINB

Read/WriteRRRRRRRR

Initial value N/A N/A N/A N/A N/A N/A N/A N/A

Port C Data Register – PORTC

Port C Data Direction Register – DDRC

Port C Input Pins Address – PINC

Port D Data Register – PORTD

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 value 0 0 0 0 0 0 0 0

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 value 0 0 0 0 0 0 0 0

Bit 76543210

PINC7 PINC6 PINC5 PINC4 PINC3 PINC2 PINC1 PINC0 PINC

Read/WriteRRRRRRRR

Initial value N/A N/A N/A N/A N/A N/A N/A N/A

In ATmega103 compatibility mode, DDRC and PINC registers are initialized to being Push-Pull Zero Output. The port pins assumes their initial value, even if the clock is not running. Note that the DDRC and PINC registers are available in ATmega103 compatibility mode, and should not be used for 100% back-ward compatibility.

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 value 0 0 0 0 0 0 0 0

Port D Data Direction Register – DDRD

Port D Input Pins Address – PIND

Port E Data Register – PORTE

ATmega128(L)

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 value 0 0 0 0 0 0 0 0

Bit 76543210

PIND7 PIND6 PIND5 PIND4 PIND3 PIND2 PIND1 PIND0 PIND

Read/WriteRRRRRRRR

Initial value N/A N/A N/A N/A N/A N/A N/A N/A

Bit 76543210

PORTE7 PORTE6 PORTE5 PORTE4 PORTE3 PORTE2 PORTE1 PORTE0 PORTE

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

2467B–09/01

ATmega128(L)

Port E Data Direction Register – DDRE

Port E Input Pins Address – PINE

Port F Data Register – PORTF

Port F Data Direction Register – DDRF

Port F Input Pins Address – PINF

Bit 76543210

DDE7 DDE6 DDE5 DDE4 DDE3 DDE2 DDE1 DDE0 DDRE

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 76543210

PINE7 PINE6 PINE5 PINE4 PINE3 PINE2 PINE1 PINE0 PINF

Read/WriteRRRRRRRR

Initial value N/A N/A N/A N/A N/A N/A N/A N/A

Bit 76543210

PORTF7 PORTF6 PORTF5 PORTF4 PORTF3 PORTF2 PORTF1 PORTF0 PORTF

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 76543210

DDF7 DDF6 DDF5 DDF4 DDF3 DDF2 DDF1 DDF0 DDRF

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 76543210

PINF7 PINF6 PINF5 PINF4 PINF3 PINF2 PINF1 PINF0 PINF

Read/WriteRRRRRRRR

Initial value N/A N/A N/A N/A N/A N/A N/A N/A

Port G Data Register – PORTG

Port G Data Direction Register – DDRG

Port G Input Pins Address – PING

Note that PORTF and DDRF registers are not available in ATmega103 compatibility mode where Port F serves as digital input only.

Bit 765 4 32 10

–––PORTG4 PORTG3 PORTG2 PORTG1 PORTG0 PORTG

Read/Write R R R R/W R/W R/W R/W R/W

Initial value 0 0 0 0 0 0 0 0

Bit 76543210

–––DDG4 DDG3 DDG2 DDG1 DDG0 DDRG

Read/Write R R R R/W R/W R/W R/W R/W

Initial value 0 0 0 0 0 0 0 0

Bit 76543210

- - - PING4 PING3 PING2 PING1 PING0 PING

Read/WriteRRRRRRRR

Initial value 0 0 0 N/A N/A N/A N/A N/A

Note that PORTG, DDRG, and PING are not available in ATmega103 compatibility mode. In the ATmega103 compatibility mode Port G serves its alternate functions only (TOSC1, TOSC2, WR

, RD and ALE).

2467B–09/01

External Interrupts The external interrupts are triggered by the INT7:0 pins. Observe that, if enabled, the

interrupts will trigger even if the INT7:0 pins are configured as outputs. This feature provides a way of generating a software interrupt. The external 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 Registers – EICRA (INT3:0) and EICRB (INT7:4). When the external interrupt is enabled and is configured as level triggered, the interrupt will trigger as long as the pin is held low. Note that recognition of falling or rising edge interrupts on INT7:4 requires the presence of an I/O clock, described in

their Distribution” on page 33

. Low level interrupts and the edge interrupt on INT3:0 are detected asynchronously. This implies that these interrupts can be used for waking the part also from sleep modes other than Idle mode. The I/O clock is halted in all sleep modes except Idle mode.

Note that if a level triggered interrupt is used for wake-up from Power-down mode, the changed level must be held for some time to wake up the MCU. This makes the MCU less sensitive to noise. The changed level is sampled twice by the watchdog oscillator clock. The period of the watchdog oscillator is 1

µs (nominal) at 5.0V and 25°C. The fre-

quency of the watchdog oscillator is voltage dependent as shown in the

Characteristics” on page 310

. The MCU will wake up if the input has the required level during this sampling or if it is held until the end of the start-up time. The start-up time is defined by the SUT fuses as described in

page 33

. If the level is sampled twice by the watchdog oscillator clock but disappears

“Clock Systems and their Distribution” on

before the end of the start-up time, the MCU will still wake up, but no interrupt will be generated. The required level must be held long enough for the MCU to complete the wake up to trigger the level interrupt.

“Clock Systems and

“Electrical

External Interrupt Control Register A – EICRA

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

This Register can not be reached in ATmega103 compatibility mode, but the initial value defines INT3:0 as low level interrupts, as in ATmega103.

• Bits 7..0 - ISC31, ISC30 - ISC00, ISC00: External Interrupt 3 - 0 Sense Control

Bits

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 interrupts are defined in

Table 48. Edges on INT3..INT0

are registered asynchronously. Pulses on INT3:0 pins wider than the minimum pulse width given in

Table 49 will generate an interrupt. Shorter pulses are not guaranteed to

generate an interrupt. If low level interrupt is selected, the low level must be held until the completion of the currently executing instruction to generate an interrupt. If enabled, a level triggered interrupt will generate an interrupt request as long as the pin is held low. When changing the ISCn bit, an interrupt can occur. Therefore, it is recommended to first disable INTn by clearing its Interrupt Enable bit in the EIMSK register. Then, the ISCn bit can be changed. Finally, the INTn interrupt flag should be cleared by writing a logical one to its Interrupt Flag bit (INTFn) in the EIFR register before the interrupt is reenabled.

ATmega128(L)

2467B–09/01

ATmega128(L)

External Interrupt Control Register B – EICRB

Table 48. Interrupt Sense Control

ISCn1 ISCn0 Description

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

01Reserved

1 0 The falling edge of INTn generates asynchronously an interrupt request.

1 1 The rising edge of INTn generates asynchronously an interrupt request.

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

(1)

Table 49. Asynchronous External Interrupt Characteristics

Symbol Parameter Condition Min Typ Max Units

INT

Bit 76543210

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial value00000000

Minimum pulse width for asynchronous external interrupt

ISC71 ISC70 ISC61 ISC60 ISC51 ISC50 ISC41 ISC40 EICRB

TBD 50 TBD ns

• Bits 7..0 - ISC71, ISC70 - ISC41, ISC40: External Interrupt 7 - 4 Sense Control

Bits

The External Interrupts 7 - 4 are activated by the external pins INT7:4 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 interrupts are defined in

Table 50. The value on the

INT7:4 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 the 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 50. 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 = 7, 6, 5 or 4.

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.

(1)

2467B–09/01

External Interrupt Mask Register – EIMSK

External Interrupt Flag Register - EIFR

Bit 76543210

INT7 INT6 INT5 INT4 INT3 INT2 INT1 IINT0 EIMSK

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial value00000000

• Bits 7..4 - INT7 - INT0: External Interrupt Request 7 - 0 Enable

When an INT7- INT4 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 Registers - EICRA and EICRB 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.

Bit 76543210

INTF7 INTF6 INTF5 INTF4 INTF3 INTF2 INTF1 IINTF0 EIFR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial value00000000

• Bits 7..0 - INTF7 - INTF0: External Interrupt Flags 7 - 0

When an edge or logic change on the INT7:0 pin triggers an interrupt request, INTF7:0 becomes set (one). If the I-bit in SREG and the corresponding interrupt enable bit, INT7:0 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 INT7:0 are configured as level interrupt. Note that when entering sleep mode with the INT3:0 interrupts disabled, the input buffers on these pins will be disabled. This may cause a logic change in internal signals which will set the INTF3:0 flags. See

on page 65

for more information.

“Digital Input Enable and Sleep Modes”

ATmega128(L)

2467B–09/01

ATmega128(L)

8-bit Timer/Counter0 with PWM and Asynchronous Operation

Timer/Counter0 is a general purpose, single channel, 8-bit Timer/Counter module. The main features are:

• Single Channel Counter

• Clear Timer on Compare Match (Auto Reload)

• Glitch-free, Phase Correct Pulse Width Modulator (PWM)

• Frequency Generator

• 10-bit Clock Prescaler

• Overflow and Compare Match Interrupt Sources (TOV0 and OCF0)

• Allows Clocking from External 32 kHz Watch Crystal Independent of the I/O Clock

Overview A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 33. For the

actual placement of I/O pins, refer to 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

page 98

Figure 33. 8-bit Timer/Counter Block Diagram

“Pin Configurations” on page 2. CPU accessible

“8-bit Timer/Counter Register Description” on

TCCRn

Timer/Counter

TCNTn

OCRn

count

clear

direction

= 0

Control Logic

TOPBOTTOM

= 0xFF

clk

Prescaler

OCn (Int.Req.)

Wavefor m Generation

T/C

Oscillator

TOVn (Int.Req.)

clk

I/O

OCn

TOSC1

TOSC2

DATA B U S

clk

I/O

clk

ASY

Status flags

Synchronized Status flags

ASSRn

asynchronous mode

select (ASn)

Synchronization Unit

Registers The Timer/Counter (TCNT0) and Output Compare Register (OCR0) are 8-bit registers.

Interrupt request (shorten as Int.Req.) signals are all visible in the Timer Interrupt Flag Register (TIFR). All interrupts are individually masked with the Timer Interrupt Mask register (TIMSK). TIFR and TIMSK are not shown in the figure since these registers are shared by other timer units.

2467B–09/01

The Timer/Counter can be clocked internally, via the prescaler, or asynchronously clocked from the TOSC1/2 pins, as detailed later in this chapter. The asynchronous operation is controlled by the Asynchronous Status Register (ASSR). The Clock Select logic block controls which clock source the Timer/Counter uses to increment (or decrement) its value. The Timer/Counter is 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 Register (OCR0) is compared with the Timer/Counter value at all times. The result of the compare can be used by the waveform generator to generate a PWM or variable frequency output on the Output Compare Pin (OC0).

See “Output Compare Unit” on page 89. for details. The compare match

event will also set the compare flag (OCF0) which can be used to generate an output compare interrupt request.

Definitions Many register and bit references in this document are written in general form. A lower

case “n” replaces the Timer/Counter number, in this case 0. However, when using the register or bit defines in a program, the precise form must be used (i.e., TCNT0 for accessing Timer/Counter0 counter value and so on).

The definitions in

Table 51 are also used extensively throughout the document.

Table 51. Definitions

BOTTOM The counter reaches the BOTTOM when it becomes zero (0x00)

MAX The counter reaches its MAXimum when it becomes 0xFF (decimal 255).

TOP The counter reaches the TOP when it becomes equal to the highest

value in the count sequence. The TOP value can be assigned to be the fixed value 0xFF (MAX) or the value stored in the OCR0 register. The assignment is dependent on the mode of operation.

Timer/Counter Clock Sources

The Timer/Counter can be clocked by an internal synchronous or an external asynchronous clock source. The clock source clk

is by default equal to the MCU clock, clk

I/O

When the AS0 bit in the ASSR register is written to logic one, the clock source is taken from the Timer/Counter Oscillator connected to TOSC1 and TOSC2. For details on asynchronous operation, see details on clock sources and prescaler, see

“Asynchronous Status Register – ASSR” on page 101. For

“Timer/Counter Prescaler” on page 104.

Counter Unit The main part of the 8-bit Timer/Counter is the programmable bidirectional counter unit.

Figure 34 shows a block diagram of the counter and its surrounding environment.

Figure 34. Counter Unit Block Diagram

DATA BU S

count

TCNTn Control Logic

clear

direction

TOVn

(Int.Req.)

clk

Prescaler

TOSC1

T/C

Oscillator

TOSC2

ATmega128(L)

topbottom

clk

I/O

2467B–09/01

Signal description (internal signals):

count Increment or decrement TCNT0 by 1.

direction Selects between increment and decrement.

clear Clear TCNT0 (set all bits to zero).

ATmega128(L)

clk

Timer/counter clock.

top Signalizes that TCNT0 has reached maximum value.

bottom Signalizes that TCNT0 has reached minimum value (zero).

Depending on the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clk

). clkT0 can be generated from an external or internal

clock source, selected by the clock select bits (CS02:0). When no clock source is selected (CS02:0 = 0) the timer is stopped. However, the TCNT0 value can be accessed by the CPU, regardless of whether clk

is present or not. A CPU write overrides (has

priority over) all counter clear or count operations.

The counting sequence is determined by the setting of the WGM01 and WGM00 bits located in the Timer/Counter control register (TCCR0). There are close connections between how the counter behaves (counts) and how waveforms are generated on the output compare output OC0. For more details about advanced counting sequences and waveform generation, see

“Modes of Operation” on page 92.

The Timer/Counter overflow (TOV0) flag is set according to the mode of operation selected by the WGM01:0 bits. TOV0 can be used for generating a CPU interrupt.

Output Compare Unit The 8-bit comparator continuously compares TCNT0 with the output compare register

(OCR0). Whenever TCNT0 equals OCR0, the comparator signals a match. A match will set the output compare flag (OCF0) at the next timer clock cycle. If enabled (OCIE0 = 1), the output compare flag generates an output compare interrupt. The OCF0 flag is automatically cleared when the interrupt is executed. Alternatively, the OCF0 flag can be cleared by software by writing a logical one to its I/O bit location. The waveform generator uses the match signal to generate an output according to operating mode set by the WGM01:0 bits and compare output mode (COM01:0) bits. The max and bottom signals are used by the waveform generator for handling the special cases of the extreme values in some modes of operation ( block diagram of the output compare unit.

“Modes of Operation” on page 92). Figure 35 shows a

2467B–09/01

Figure 35. Output Compare Unit, Block Diagram

DATA BU S

OCRn

TCNTn

= (8-bit Comparator )

OCFn (Int.Req.)

top

bottom

FOCn

The OCR0 register is double buffered when using any of the pulse width modulation (PWM) modes. For the normal and clear timer on compare (CTC) modes of operation, the double buffering is disabled. The double buffering synchronizes the update of the OCR0 compare register to either top or bottom of the counting sequence. The synchronization prevents the occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.

Waveform Generator

WGMn1:0

COMn1:0

OCxy

The OCR0 register access may seem complex, but this is not case. When the double buffering is enabled, the CPU has access to the OCR0 buffer register, and if double buffering is disabled the CPU will access the OCR0 directly.

Force Output Compare In non-PWM waveform generation modes, the match output of the comparator can be

forced by writing a one to the force output compare (FOC0) bit. Forcing compare match will not set the OCF0 flag or reload/clear the timer, but the OC0 pin will be updated as if a real compare match had occurred (the COM01:0 bits settings define whether the OC0 pin is set, cleared or toggled).

Compare Match Blocking by TCNT0 Write

All CPU write operations to the TCNT0 register will block any compare match that occurs in the next timer clock cycle, even when the timer is stopped. This feature allows OCR0 to be initialized to the same value as TCNT0 without triggering an interrupt when the Timer/Counter clock is enabled.

Using the Output Compare Unit

Since writing TCNT0 in any mode of operation will block all compare matches for one timer clock cycle, there are risks involved when changing TCNT0 when using the output compare channel, independently of whether the Timer/Counter is running or not. If the value written to TCNT0 equals the OCR0 value, the compare match will be missed, resulting in incorrect waveform generation. Similarly, do not write the TCNT0 value equal to BOTTOM when the counter is downcounting.

ATmega128(L)

2467B–09/01

ATmega128(L)

The setup of the OC0 should be performed before setting the data direction register for the port pin to output. The easiest way of setting the OC0 value is to use the force output compare (FOC0) strobe bit in normal mode. The OC0 register keeps its value even when changing between waveform generation modes.

Be aware that the COM01:0 bits are not double buffered together with the compare value. Changing the COM01:0 bits will take effect immediately.

Compare Match Output Unit

The compare output mode (COM01:0) bits have two functions. The waveform generator uses the COM01:0 bits for defining the output compare (OC0) state at the next compare match. Also, the COM01:0 bits control the OC0 pin output source.

Figure 36 shows a

simplified schematic of the logic affected by the COM01:0 bit setting. The I/O registers, I/O bits, and I/O pins in the figure are shown in bold. Only the parts of the general I/O port control registers (DDR and PORT) that are affected by the COM01:0 bits are shown. When referring to the OC0 state, the reference is for the internal OC0 register, not the OC0 pin.

Figure 36. Compare Match Output Unit, Schematic

COMn1

COMn0 FOCn

Waveform Generator

OCn

PORT

DATA BU S

OCn

Compare Output Mode and Waveform Generation

2467B–09/01

clk

I/O

DDR

The general I/O port function is overridden by the output compare (OC0) from the waveform generator if either of the COM01:0 bits are set. However, the OC0 pin direction (input or output) is still controlled by the data direction register (DDR) for the port pin. The data direction register bit for the OC0 pin (DDR_OC0) must be set as output before the OC0 value is visible on the pin. The port override function is independent of the waveform generation mode.

The design of the output compare pin logic allows initialization of the OC0 state before the output is enabled. Note that some COM01:0 bit settings are reserved for certain modes of operation.

See “8-bit Timer/Counter Register Description” on page 98.

The waveform generator uses the COM01:0 bits differently in normal, CTC, and PWM modes. For all modes, setting the COM01:0 = 0 tells the waveform generator that no action on the OC0 register is to be performed on the next compare match. For compare output actions in the non-PWM modes refer to

Table 53 on page 99. For fast PWM

mode, refer to Table 54 on page 99, and for phase correct PWM refer to Table 55 on

page 100

A change of the COM01:0 bits state will have effect at the first compare match after the bits are written. For non-PWM modes, the action can be forced to have immediate effect by using the FOC0 strobe bits.

Modes of Operation The mode of operation, i.e. the behavior of the Timer/Counter and the output compare

pins, is defined by the combination of the waveform generation mode (WGM01:0) and compare output mode (COM01:0) bits. The compare output mode bits do not affect the counting sequence, while the waveform generation mode bits do. The COM01:0 bits control whether the PWM output generated should be inverted or not (inverted or noninverted PWM). For non-PWM modes the COM01:0 bits control whether the output should be set, cleared, or toggled at a compare match (

Unit” on page 91.

See “Compare Match Output

For detailed timing information refer to

Normal Mode The simplest mode of operation is the normal mode (WGM01:0 = 0). In this mode the

counting direction is always up (incrementing), and no counter clear is performed. The counter simply overruns when it passes its maximum 8-bit value (TOP = 0xFF) and then restarts from the 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 9th bit, except that it is only set, not cleared. However, combined with the timer overflow interrupt that automatically clears 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.

Clear Timer on Compare Match (CTC) Mode

In clear timer on compare or CTC mode (WGM01:0 = 2), the OCR0 register is used to manipulate the counter resolution. In CTC mode the counter is cleared to zero when the counter value (TCNT0) matches the OCR0. The OCR0 defines the top value for the counter, hence also its resolution. This mode allows greater control of the compare match output frequency. It also simplifies the operation of counting external events.

The timing diagram for the CTC mode is shown in (TCNT0) increases until a compare match occurs between TCNT0 and OCR0, and then counter (TCNT0) is cleared.

“Timer/Counter Timing Diagrams” on page 96.

TOV0 flag, the

Figure 37. The counter value

ATmega128(L)

2467B–09/01

Figure 37. CTC Mode, Timing Diagram

TCNTn

ATmega128(L)

OCn Interrupt Flag Set

OCn (Toggle)

Period

1 4

2 3

(COMn1:0 = 1)

An interrupt can be generated each time the counter value reaches the TOP value by using the OCF0 flag. If the interrupt is enabled, the interrupt handler routine can be used for updating the TOP value. However, changing the TOP to a value close to BOTTOM when the counter is running with none or a low prescaler value must be done with care since the CTC mode does not have the double buffering feature. If the new value written to OCR0 is lower than the current value of TCNT0, the counter will miss the compare match. The counter will then have to count to its maximum value (0xFF) and wrap around starting at 0x00 before the compare match can occur.

For generating a waveform output in CTC mode, the OC0 output can be set to toggle its logical level on each compare match by setting the compare output mode bits to toggle mode (COM01:0 = 1). The OC0 value will not be visible on the port pin unless the data direction for the pin is set to output. The waveform generated will have a maximum frequency of f

OC0

= f

/2 when OCR0 is set to zero (0x00). The waveform frequency is

clk_I/O

defined by the following equation:

OCn

clk_I/O

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

2 N 1 OCRn+()⋅⋅

The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).

As for the normal mode of operation, the

TOV0 flag is set in the same timer clock cycle

that the counter counts from MAX to 0x00.

Fast PWM Mode The fast pulse width modulation or fast PWM mode (WGM01:0 = 1) provides a high fre-

quency PWM waveform generation option. The fast PWM differs from the other PWM option by its single-slope operation. The counter counts from BOTTOM to MAX then restarts from BOTTOM. In non-inverting compare output mode, the output compare (OC0) is cleared on the compare match between TCNT0 and OCR0, and set at BOTTOM. In inverting compare output mode, the output is set on compare match and cleared at BOTTOM. Due to the single-slope operation, the operating frequency of the fast PWM mode can be twice as high as the phase correct PWM mode that uses dualslope operation. This high frequency makes the fast PWM mode well suited for power regulation, rectification, and DAC applications. High frequency allows physically small sized external components (coils, capacitors), and therefore reduces total system cost.

In fast PWM mode, the counter is incremented until the counter value matches the MAX value. The counter is then cleared at the following timer clock cycle. The timing diagram for the fast PWM mode is shown in

Figure 38. The TCNT0 value is in the timing diagram

shown as a histogram for illustrating the single-slope operation. The diagram includes

2467B–09/01

non-inverted and inverted PWM outputs. The small horizontal line marks on the TCNT0 slopes represent compare matches between OCR0 and TCNT0.

Figure 38. Fast PWM Mode, Timing Diagram

OCRn Interrupt Flag Set

OCRn Update and TOVn Interrupt Flag Set

TCNTn

OCn

Period

2 3

The Timer/Counter overflow flag (

4 5 6 7

TOV0) is set each time the counter reaches Max If the

(COMn1:0 = 2)

(COMn1:0 = 3)

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 OC0 pin. Setting the COM01:0 bits to 2 will produce a non-inverted PWM and an inverted PWM output can be generated by setting the COM01:0 to 3 (See

Table 54 on page 99).

The actual OC0 value will only be visible on the port pin if the data direction for the port pin is set as output. The PWM waveform is generated by setting (or clearing) the OC0 register at the compare match between OCR0 and TCNT0, and clearing (or setting) the OC0 register at the timer clock cycle the counter is cleared (changes from MAX to BOTTOM).

The PWM frequency for the output can be calculated by the following equation:

OCnPWM

clk_I/O

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

N 256⋅

The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).

The extreme values for the OCR0 register represent special cases when generating a PWM waveform output in the fast PWM mode. If the OCR0 is set equal to BOTTOM, the output will be a narrow spike for each MAX+1 timer clock cycle. Setting the OCR0 equal to MAX will result in a constantly high or low output (depending on the polarity of the output set by the COM01:0 bits.)

A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting OC0 to toggle its logical level on each compare match (COM01:0 = 1). The waveform generated will have a maximum frequency of f to zero. This feature is similar to the OC0 toggle in CTC mode, except the double buffer feature of the output compare unit is enabled in the fast PWM mode.

ATmega128(L)

oc0

= f

/2 when OCR0 is set

clk_I/O

2467B–09/01

ATmega128(L)

Phase Correct PWM Mode The phase correct PWM mode (WGM01:0 = 3) provides a high resolution phase correct

PWM waveform generation option. The phase correct PWM mode is based on a dualslope operation. The counter counts repeatedly from BOTTOM to MAX and then from MAX to BOTTOM. In non-inverting compare output mode, the output compare (OC0) is cleared on the compare match between TCNT0 and OCR0 while 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.

The PWM resolution for the phase correct PWM mode is fixed to 8 bits. In phase correct PWM mode the counter is incremented until the counter value matches Max When the counter reaches MAX, it changes the count direction. The TCNT0 value will be equal to MAX for one timer clock cycle. The timing diagram for the phase correct PWM mode is shown on for illustrating the dual-slope operation. The diagram includes non-inverted and inverted PWM outputs. The small horizontal line marks on the TCNT0 slopes represent compare matches between OCR0 and TCNT0.

Figure 39. Phase Correct PWM Mode, Timing Diagram

Figure 39. The TCNT0 value is in the timing diagram shown as a histogram

OCn Interrupt Flag Set

OCRn Update

TOVn Interrupt Flag Set

TCNTn

OCn

Period

1 2 3

The Timer/Counter overflow flag (

TOV0) is set each time the counter reaches BOTTOM.

(COMn1:0 = 2)

(COMn1:0 = 3)

The interrupt flag can be used to generate an interrupt each time the counter reaches the BOTTOM value.

In phase correct PWM mode, the compare unit allows generation of PWM waveforms on the OC0 pin. Setting the COM01:0 bits to 2 will produce a non-inverted PWM. An inverted PWM output can be generated by setting the COM01:0 to 3 (See

page 100

). The actual OC0 value will only be visible on the port pin if the data direction

Table 55 on

for the port pin is set as output. The PWM waveform is generated by clearing (or setting) the OC0 register at the compare match between OCR0 and TCNT0 when the counter increments, and setting (or clearing) the OC0 register at compare match between OCR0

2467B–09/01

and TCNT0 when the counter decrements. The PWM frequency for the output when using phase correct PWM can be calculated by the following equation:

clk_I/O

OCnPCPWM

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

N 510⋅

The N variable represents the prescale factor (1, 8, 32, 64, 128, 256, or 1024).

The extreme values for the OCR0 register represent special cases when generating a PWM waveform output in the phase correct PWM mode. If the OCR0 is set equal to BOTTOM, the 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.

Timer/Counter Timing Diagrams

Figure 40 and Figure 41 contain timing data for the Timer/Counter operation. The

Timer/Counter is a synchronous design and the timer clock (clk

) is therefore shown as

a clock enable signal. The figure shows the count sequence close to the MAX value.

Figure 42 and Figure 43 show the same timing data, but with the prescaler enabled. The

figures illustrate when interrupt flags are set.

The following figures show the Timer/Counter in synchronous mode, and the timer clock

) is therefore shown as a clock enable signal. In asynchronous mode, clk

(clk

should

I/O

be replaced by the Timer/Counter Oscillator clock. The figures include information on when interrupt flags are set.

Figure 40 contains timing data for basic Timer/Counter

operation. The figure shows the count sequence close to the MAX value in all modes other than phase correct PWM mode.

Figure 40. Timer/Counter Timing Diagram, No Prescaling

clk

I/O

clk

(clk

/1)

I/O

TCNTn

MAX - 1 MAX BOTTOM BOTTOM + 1

TOVn

Figure 41 shows the same timing data, but with the prescaler enabled.

ATmega128(L)

2467B–09/01

ATmega128(L)

Figure 41. Timer/Counter Timing Diagram, with Prescaler (f

clk

I/O

clk

(clk

/8)

I/O

TCNTn

MAX - 1 MAX BOTTOM BOTTOM + 1

clk_I/O

/8)

TOVn

Figure 42 shows the setting of OCF0 in all modes except CTC mode.

Figure 42. Timer/Counter Timing Diagram, Setting of OCF0, With Prescaler (f

clk

I/O

clk

(clk

/8)

I/O

clk_I/O

/8)

TCNTn

OCRn

OCRn - 1 OCRn OCRn + 1 OCRn + 2

OCRn Value

OCFn

Figure 43 shows the setting of OCF0 and the clearing of TCNT0 in CTC mode.

2467B–09/01

Figure 43. Timer/Counter Timing Diagram, Clear Timer on Compare Match Mode, with

Prescaler (f

clk

I/O

clk

(clk

/8)

I/O

clk_I/O

/8)

8-bit Timer/Counter Register Description

Timer/Counter Control Register - TCCR0

TCNTn

(CTC)

OCRn

TOP - 1 TOP BOTTOM BOTTOM + 1

TOP

OCFn

Bit 76543210

FOC0 WGM00 COM01 COM00 WGM01 CS02 CS01 CS00 TCCR0

Read/Write W R/W R/W R/W R/W R/W R/W R/W

Initial value00000000

• Bit 7 - FOC0: Force Output Compare

The FOC0 bit is only active when the WGM bits specify a non-PWM mode. However, for ensuring compatibility with future devices, this bit must be set to zero when TCCR0 is written when operating in PWM mode. When writing a logical one to the FOC0 bit, an immediate compare match is forced on the waveform generation unit. The OC0 output is changed according to its COM01:0 bits setting. Note that the FOC0 bit is implemented as a strobe. Therefore it is the value present in the COM01:0 bits that determines the effect of the forced compare.

A FOC0 strobe will not generate any interrupt, nor will it clear the timer in CTC mode using OCR0 as TOP.

The FOC0 bit is always read as zero.

• Bit 6,3 - WGM01:0: Waveform Generation Mode

These bits control the counting sequence of the counter, the source for the maximum (TOP) counter value, and what type of waveform generation to be used. Modes of operation supported by the Timer/Counter unit are: Normal mode, Clear Timer on Compare match (CTC) mode, and two types of Pulse Width Modulation (PWM) modes. See

ATmega128(L)

Table

and “Modes of Operation” on page 92.

2467B–09/01

ATmega128(L)

Table 52. Waveform Generation Mode Bit Description

(CTC0)

(1)

WGM00

WGM01

Mode

0 0 0 Normal 0xFF Immediate MAX

(PWM0)

(1)

Timer/Counter Mode of Operation TOP

Update of OCR0 at

TOV0 Flag Set on

1 0 1 PWM, Phase

Correct

2 1 0 CTC OCR0 Immediate MAX

31 1Fast PWM 0xFFTOPMAX

Note: 1. The CTC0 and PWM0 bit definition names are now obsolete. Use the WGM01:0 def-

initions. However, the functionality and location of these bits are compatible with previous versions of the timer.

0xFF TOP BOTTOM

• Bit 5:4 - COM01:0: Compare Match Output Mode

These bits control the output compare pin (OC0) behavior. If one or both of the COM01:0 bits are set, the OC0 output overrides the normal port functionality of the I/O pin it is connected to. However, note that the Data Direction Register (DDR) bit corresponding to OC0 pin must be set in order to enable the output driver.

When OC0 is connected to the pin, the function of the COM01:0 bits depends on the WGM01:0 bit setting.

Table 53 shows the COM01:0 bit functionality when the WGM01:0

bits are set to a normal or CTC mode (non-PWM).

Table 53. Compare Output Mode, Non-PWM Mode

COM01 COM00 Description

0 0 Normal port operation, OC0 disconnected.

0 1 Toggle OC0 on compare match

1 0 Clear OC0 on compare match

1 1 Set OC0 on compare match

Table 54 shows the COM01:0 bit functionality when the WGM01:0 bits are set to fast

PWM mode.

Table 54. Compare Output Mode, Fast PWM Mode

COM01 COM00 Description

0 0 Normal port operation,

01Reserved

10Clear

11Set

Note: 1. A special case occurs when OCR0 equals TOP and COM01 is set. In this case, the

compare match is ignored, but the set or clear is done at TOP. See “Fast PWM Mode” on page 93 for more details.

OC0 on compare match, set OC0 at TOP

OC0 on compare match, clear OC0 at TOP

(1)

OC0 disconnected.

Table 55 shows the COM01:0 bit functionality when the WGM01:0 bits are set to phase

correct PWM mode.

2467B–09/01

Table 55. Compare Output Mode, Phase Correct PWM Mode

COM01 COM00 Description

0 0 Normal port operation, OC0 disconnected.

01Reserved

(1)

1 0 Clear

OC0 on compare match when up-counting. Set OC0 on compare

match when downcounting.

11Set

OC0 on compare match when up-counting. Clear OC0 on compare

match when downcounting.

Note: 1. A special case occurs when OCR0 equals TOP and COM01 is set. In this case, the

compare match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” on page 95 for more details.

• Bit 2:0 - CS02:0: Clock Select

The three clock select bits select the clock source to be used by the Timer/Counter, see

Table 56.

Table 56. Clock Select Bit Description

CS02 CS01 CS00 Description

0 0 0 No clock source (Timer/counter stopped)

001

010clk

011

100

101clk

110clk

111clk

clk

/(No prescaling)

T0S

/8 (From prescaler)

T0S

clk

/32 (From prescaler)

T0S

clk

/64 (From prescaler)

T0S

/128 (From prescaler)

T0S

/256 (From prescaler)

T0S

/1024 (From prescaler)

T0S

Timer/Counter Register – TCNT0

Output Compare Register – OCR0

100

ATmega128(L)

Bit 76543210

TCNT0[7:0] TCNT0

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial value00000000

The Timer/Counter Register gives direct access, both for read and write operations, to the Timer/Counter unit 8-bit counter. Writing to the TCNT0 register blocks (removes) the compare match on the following timer clock. Modifying the counter (TCNT0) while the counter is running, introduces a risk of missing a compare match between TCNT0 and the OCR0 register.

Bit 76543210

OCR0[7:0] OCR0

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial value00000000

The Output Compare Register contains an 8-bit value that is continuously compared with the counter value (TCNT0). A match can be used to generate an output compare interrupt, or to generate a waveform output on the OC0 pin.

2467B–09/01

Rainbow Electronics ATmega128L User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Features

Pin Configurations Figure 1. Pinout ATmega128

Overview The ATmega128 is a low-power CMOS 8-bit microcontroller based on the AVR

Block Diagram

ATmega103 and ATmega128 Compatibility

ATmega103 Compatibility Mode

Pin Descriptions

Port A (PA7..PA0) Port A is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each

Port B (PB7..PB0) Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each

Port C (PC7..PC0) Port C is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each

Port D (PD7..PD0) Port D is an 8-bit bidirectional I/O port with internal pull-up resistors (selected for each

Port E (PE7..PE0) Port E is an 8-bit bidirectional I/O port with internal pull-up resistors (selected for each

Port F (PF7..PF0) Port F serves as the analog inputs to the A/D Converter.

Port G (PG4..PG0) Port G is a 5-bit bidirectional I/O port with internal pull-up resistors (selected for each

RESET

XTAL1 Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

XTAL2 Output from the inverting oscillator amplifier.

AVCC This is the supply voltage pin for Port F and the A/D Converter. It should be externally

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

About Code Examples

AVR CPU Core

Introduction This chapter discusses the AVR core architecture in general. The main function of the

Architectural Overview Figure 3. Block Diagram of the AVR Architecture

ALU – Arithmetic Logic Unit

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

General Purpose Register File

Stack Pointer The stack is mainly used for storing temporary data, for storing local variables and for

RAM Page Z Select Register – RAMPZ

Instruction Execution Timing

Reset and Interrupt Handling

Interrupt Response Time The interrupt execution response for all the enabled AVR interrupts is 4 clock cycles

AVR ATmega128 Memories

In-System Reprogrammable Flash Program Memory

SRAM Data Memory The ATmega128 supports two different configurations for the SRAM data memory as

Data Memory Access Times This section describes the general access timing concepts for internal memory access.

EEPROM Data Memory The ATmega128 contains 4K bytes of data EEPROM memory. It is organized as a sep-

EEPROM Read/Write Access The EEPROM access registers are accessible in the I/O space.

EEPROM Address Register – EEARH and EEARL

EEPROM Data Register – EEDR

EEPROM Control Register – EECR

Preventing EEPROM Corruption

I/O Memory The I/O space definition of the ATmega128 is shown in “Register Summary” on page

External Memory Interface

Overview When the eXternal MEMory (XMEM) is enabled, address space outside the internal

ATmega103 Compatibility Both External Memory Control Registers (XMCRA and XMCRB) are placed in Extended

Using the External Memory Interface

Address Latch Requirements Due to the high-speed operation of the XRAM interface, the address latch must be

Pull-up and Bus-keeper The pull-ups on the AD7:0 ports may be activated if the corresponding Port register is

Timing External memory devices have different timing requirements. To meet these require-

XMEM Register Description

MCU Control Register – MCUCR

External Memory Control Register A – XMCRA

External Memory Control Register B – XMCRB

Using all 64KB Locations of External Memory

System Clock and Clock Options

Clock Systems and their Distribution

Clock Sources The device has the following clock source options, selectable by Flash fuse bits as

Crystal Oscillator XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can

Low-frequency Crystal Oscillator

External RC Oscillator For timing insensitive applications, the external RC configuration shown in Figure 19

Calibrated Internal RC Oscillator

Oscillator Calibration Register – OSCCAL

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

Timer/Counter Oscillator For AVR microcontrollers with Timer/Counter Oscillator pins (TOSC1 and TOSC2), the

XTAL Divide Control Register – XDIV

Power Management and Sleep Modes

MCU Control Register – MCUCR

Idle Mode When the SM2..0 bits are written to 000, the SLEEP instruction makes the MCU enter

ADC Noise Reduction Mode

Power-down Mode When the SM2..0 bits are written to 010, the SLEEP instruction makes the MCU enter

Power-save Mode When the SM2..0 bits are written to 011, the SLEEP instruction makes the MCU enter

Standby Mode When the SM2..0 bits are 110 and an external crystal/resonator clock option is selected,

Extended Standby Mode When the SM2..0 bits are 111 and an external crystal/resonator clock option is selected,

Minimizing Power Consumption

Analog to Digital Converter If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should

Analog Comparator When entering Idle Mode, the Analog Comparator should be disabled if not used. When