Atmel Electronic Components Datasheet



ATMEGA128

8-bit Atmel Microcontroller


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Features
High-performance, Low-power Atmel®AVR®8-bit Microcontroller
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 16MIPS Throughput at 16MHz
– On-chip 2-cycle Multiplier
High Endurance Non-volatile Memory segments
– 128Kbytes of In-System Self-programmable Flash program memory
– 4Kbytes EEPROM
– 4Kbytes Internal SRAM
– Write/Erase cycles: 10,000 Flash/100,000 EEPROM
– Data retention: 20 years at 85°C/100 years at 25°C(1)
– Optional Boot Code Section with Independent Lock Bits
In-System Programming by On-chip Boot Program
True Read-While-Write Operation
– Up to 64Kbytes Optional External Memory Space
– Programming Lock for Software Security
– SPI Interface for In-System Programming
QTouch® library support
– Capacitive touch buttons, sliders and wheels
– QTouch and QMatrix acquisition
– Up to 64 sense channels
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 2 to 16 Bits
– Output Compare Modulator
– 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 Two-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 and 64-pad QFN/MLF
Operating Voltages
– 2.7 - 5.5V ATmega128L
– 4.5 - 5.5V ATmega128
Speed Grades
– 0 - 8MHz ATmega128L
– 0 - 16MHz ATmega128
8-bit Atmel
Microcontroller
with 128KBytes
In-System
Programmable
Flash
ATmega128
ATmega128L
Rev. 2467X–AVR–06/11


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Pin
Configurations
Figure 1. Pinout ATmega128
PEN
RXD0/(PDI) PE0
(TXD0/PDO) PE1
(XCK0/AIN0) PE2
(OC3A/AIN1) PE3
(OC3B/INT4) PE4
(OC3C/INT5) PE5
(T3/INT6) PE6
(ICP3/INT7) PE7
(SS) PB0
(SCK) PB1
(MOSI) PB2
(MISO) PB3
(OC0) PB4
(OC1A) PB5
(OC1B) PB6
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
ATmega128
48 PA3 (AD3)
47 PA4 (AD4)
46 PA5 (AD5)
45 PA6 (AD6)
44 PA7 (AD7)
43 PG2(ALE)
42 PC7 (A15)
41 PC6 (A14)
40 PC5 (A13)
39 PC4 (A12)
38 PC3 (A11)
37 PC2 (A10)
36 PC1 (A9)
35 PC0 (A8)
34 PG1(RD)
33 PG0(WR)
Overview
2467X–AVR–06/11
Note: The Pinout figure applies to both TQFP and MLF packages. The bottom pad under the QFN/MLF
package should be soldered to ground.
The Atmel® AVR® 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 1MIPS per MHz allowing the system designer to
optimize power consumption versus processing speed.
2


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Block Diagram
Figure 2. Block Diagram
ATmega128
VCC
GND
PF0 - PF7
PORTF DRIVERS
PA0 - PA7
PORTA DRIVERS
PC0 - PC7
PORTC DRIVERS
DATA REGISTER
PORTF
DATA DIR.
REG. PORTF
DATA REGISTER
PORTA
DATA DIR.
REG. PORTA
DATA REGISTER
PORTC
8-BIT DATA BUS
DATA DIR.
REG. PORTC
AVCC
AGND
AREF
JTAG TAP
ON-CHIP DEBUG
BOUNDARY-
SCAN
PEN
PROGRAMMING
LOGIC
ADC
PROGRAM
COUNTER
PROGRAM
FLASH
INSTRUCTION
REGISTER
INSTRUCTION
DECODER
CONTROL
LINES
USART0
STACK
POINTER
SRAM
GENERAL
PURPOSE
REGISTERS
X
Y
Z
ALU
STATUS
REGISTER
INTERNAL
OSCILLATOR
WATCHDOG
TIMER
MCU CONTROL
REGISTER
TIMER/
COUNTERS
INTERRUPT
UNIT
EEPROM
CALIB. OSC
OSCILLATOR
OSCILLATOR
TIMING AND
CONTROL
SPI
USART1
TWO-WIRE SERIAL
INTERFACE
DATA REGISTER
PORTE
DATA DIR.
REG. PORTE
DATA REGISTER
PORTB
DATA DIR.
REG. PORTB
DATA REGISTER
PORTD
DATA DIR.
REG. PORTD
DATA REG. DATA DIR.
PORTG REG. PORTG
PORTE DRIVERS
PORTB DRIVERS
PORTD DRIVERS
PORTG DRIVERS
PE0 - PE7
PB0 - PB7
PD0 - PD7
PG0 - PG4
2467X–AVR–06/11
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ATmega128
ATmega103 and
ATmega128
Compatibility
The Atmel® AVR® core combines a rich instruction set with 32 general purpose working regis-
ters. 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: 128Kbytes of In-System Programmable Flash
with Read-While-Write capabilities, 4Kbytes EEPROM, 4Kbytes SRAM, 53 general purpose I/O
lines, 32 general purpose working registers, Real Time Counter (RTC), four flexible Timer/Coun-
ters with compare modes and PWM, 2 USARTs, a byte oriented Two-wire Serial Interface, an 8-
channel, 10-bit ADC with optional differential input stage with programmable gain, programma-
ble 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 contin-
ues 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.
Atmel offers the QTouch® library for embedding capacitive touch buttons, sliders and wheels
functionality into AVR microcontrollers. The patented charge-transfer signal acquisition offers
robust sensing and includes fully debounced reporting of touch keys and includes Adjacent Key
Suppression® (AKS) technology for unambiguous detection of key events. The easy-to-use
QTouch Suite toolchain allows you to explore, develop and debug your own touch applications.
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 effec-
tive solution to many embedded control applications.
The ATmega128 device 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 super-
sedes the 64 I/O locations 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 locations can be reached by using
LD/LDS/LDD and ST/STS/STD instructions only, not by using IN and OUT instructions. The relo-
cation 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.
2467X–AVR–06/11
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ATmega128
ATmega103
Compatibility Mode
Pin Descriptions
VCC
GND
Port A (PA7..PA0)
Port B (PB7..PB0)
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.
By programming the M103C fuse, the Atmel®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 eight least significant bits of
the Baud Rate Register is available.
• One 16 bits Timer/Counter with two compare registers instead of two 16-bit Timer/Counters
with three compare registers.
• Two-wire serial interface is not supported.
• Port C is output only.
• 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.
In addition, there are some other minor differences to make it more compatible to ATmega103:
• Only EXTRF and PORF exists in MCUCSR.
• Timed sequence not required for Watchdog Time-out change.
• External Interrupt pins 3 - 0 serve as level interrupt only.
• USART has no FIFO buffer, so data overrun comes earlier.
Unused I/O bits in ATmega103 should be written to 0 to ensure same operation in ATmega128.
Digital supply voltage.
Ground.
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 on page
72.
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 on page
73.
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ATmega128
Port C (PC7..PC0)
Port D (PD7..PD0)
Port E (PE7..PE0)
Port F (PF7..PF0)
Port G (PG4..PG0)
Port C is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port C output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port C pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port C pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port C also serves the functions of special features of the Atmel® AVR®ATmega128 as listed on
page 76. In ATmega103 compatibility mode, Port C is output only, and the port C pins are not tri-
stated when a reset condition becomes active.
Note:
The ATmega128 is by default shipped in ATmega103 compatibility mode. Thus, if the parts are not
programmed before they are put on the PCB, PORTC will be output during first power up, and until
the ATmega103 compatibility mode is disabled.
Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port D output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port D pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port D pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port D also serves the functions of various special features of the ATmega128 as listed on page
77.
Port E is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port E output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port E pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port E pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port E also serves the functions of various special features of the ATmega128 as listed on page
80.
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 sym-
metrical 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.
The TDO pin is tri-stated unless TAP states that shift out data are entered.
Port F also serves the functions of the JTAG interface.
In ATmega103 compatibility mode, Port F is an input Port only.
Port G is a 5-bit bi-directional 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.
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RESET
XTAL1
XTAL2
AVCC
AREF
PEN
ATmega128
In ATmega103 compatibility mode, these pins only serves as strobes signals to the external
memory as well as input to the 32kHz 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 input. A low level on this pin for longer than the minimum pulse length will generate a
reset, even if the clock is not running. The minimum pulse length is given in Table 19 on page
50. Shorter pulses are not guaranteed to generate a reset.
Input to the inverting Oscillator amplifier and input to the internal clock operating circuit.
Output from the inverting Oscillator amplifier.
AVCC is the supply voltage pin for Port F and the A/D Converter. It should be externally con-
nected 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 is the analog reference pin for the A/D Converter.
PEN is a programming enable pin for the SPI Serial Programming mode, and is internally pulled
high . By holding this pin low during a Power-on Reset, the device will enter the SPI Serial Pro-
gramming mode. PEN has no function during normal operation.
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ATmega128
Resources
A comprehensive set of development tools, application notes, and datasheets are available for
download on http://www.atmel.com/avr.
Note: 1.
Data Retention Reliability Qualification results show that the projected data retention failure rate is much less
than 1 PPM over 20 years at 85°C or 100 years at 25°C
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 compi-
lation. 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.
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI”
instructions must be replaced with instructions that allow access to extended I/O. Typically
“LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
Capacitive touch sensing
The Atmel QTouch Library provides a simple to use solution to realize touch sensitive interfaces
on most Atmel AVR microcontrollers. The QTouch Library includes support for the QTouch and
QMatrix acquisition methods.
Touch sensing can be added to any application by linking the appropriate Atmel QTouch Library
for the AVR Microcontroller. This is done by using a simple set of APIs to define the touch chan-
nels and sensors, and then calling the touch sensing API’s to retrieve the channel information
and determine the touch sensor states.
The QTouch Library is FREE and downloadable from the Atmel website at the following location:
www.atmel.com/qtouchlibrary. For implementation details and other information, refer to the
Atmel QTouch Library User Guide - also available for download from the Atmel website.
2467X–AVR–06/11
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ATmega128
AVR CPU Core
Introduction
Architectural
Overview
This section discusses the Atmel® 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.
Figure 3. Block Diagram of the AVR Architecture
Data Bus 8-bit
Flash
Program
Memory
Instruction
Register
Instruction
Decoder
Control Lines
Program
Counter
Status
and Control
32 x 8
General
Purpose
Registrers
ALU
Interrupt
Unit
SPI
Unit
Watchdog
Timer
Analog
Comparator
Data
SRAM
EEPROM
I/O Module1
I/O Module 2
I/O Module n
I/O Lines
In order to maximize performance and parallelism, the AVR uses a Harvard architecture – with
separate memories and buses for program and data. Instructions in the program memory are
executed with a single level pipelining. While one instruction is being executed, the next instruc-
tion is pre-fetched from the program memory. This concept enables instructions to be executed
in every clock cycle. The program memory is In-System Reprogrammable Flash memory.
The fast-access Register file contains 32 x 8-bit general purpose working registers with a single
clock cycle access time. This allows single-cycle Arithmetic Logic Unit (ALU) operation. In a typ-
ical ALU operation, two operands are output from the Register file, the operation is executed,
and the result is stored back in the Register file – in one clock cycle.
Six of the 32 registers can be used as three 16-bit indirect address register pointers for Data
Space addressing – enabling efficient address calculations. One of the these address pointers
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 an arithmetic opera-
tion, the Status Register is updated to reflect information about the result of the operation.
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ATmega128
Program flow is provided by conditional and unconditional jump and call instructions, able to
directly address the whole address space. Most AVR instructions have a single 16-bit word for-
mat. Every program memory address contains a 16-bit or 32-bit instruction.
Program Flash memory space is divided in two sections, the Boot Program section and the
Application Program section. Both sections have dedicated Lock bits for write and read/write
protection. The SPM instruction that writes into the Application Flash Memory section must
reside in the Boot Program section.
During interrupts and subroutine calls, the return address Program Counter (PC) is stored on the
Stack. The Stack is effectively allocated in the general data SRAM, and consequently the stack
size is only limited by the total SRAM size and the usage of the SRAM. All user programs must
initialize the SP in the reset routine (before subroutines or interrupts are executed). The Stack
Pointer – SP – is read/write accessible in the I/O space. The data SRAM can easily be accessed
through the five different addressing modes supported in the AVR architecture.
The memory spaces in the AVR architecture are all linear and regular memory maps.
A flexible interrupt module has its control registers in the I/O space with an additional global
interrupt enable bit in the Status Register. All interrupts have a separate interrupt vector in the
interrupt vector table. The interrupts have priority in accordance with their interrupt vector posi-
tion. The lower the interrupt vector address, the higher the priority.
The I/O memory space contains 64 addresses 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 “Instruction Set” section for a detailed description.
Status Register
The Status Register contains information about the result of the most recently executed arithme-
tic instruction. This information can be used for altering program flow in order to perform
conditional operations. Note that the Status Register is updated after all ALU operations, as
specified in the Instruction Set Reference. This will in many cases remove the need for using the
dedicated compare instructions, resulting in faster and more compact code.
The status register is not automatically stored when entering an interrupt routine and restored
when returning from an interrupt. This must be handled by software.
The AVR status Register – SREG – is defined as:
Bit
Read/Write
Initial Value
76543210
I T H S V N Z C SREG
R/W R/W R/W R/W R/W R/W R/W R/W
00000000
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ATmega128
General Purpose
Register File
• Bit 7 – I: Global Interrupt Enable
The Global Interrupt Enable bit must be set for the interrupts to be enabled. The individual inter-
rupt enable control is then performed in separate control registers. If the Global Interrupt Enable
Register is cleared, none of the interrupts are enabled independent of the individual interrupt
enable settings. The I-bit is cleared by hardware after an interrupt has occurred, and is set by
the RETI instruction to enable subsequent interrupts. The I-bit can also be set and cleared 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 desti-
nation for the operated bit. A bit from a register in the Register file can be copied into T by the
BST instruction, and a bit in T can be copied into a bit in a register in the Register file by the BLD
instruction.
• Bit 5 – H: Half Carry Flag
The Half Carry Flag H indicates a half carry in some arithmetic operations. Half carry is useful in
BCD arithmetic. See the “Instruction Set Description” for detailed information.
• Bit 4 – S: Sign Bit, S = N V
The S-bit is always an exclusive or between the negative flag N and the two’s complement over-
flow flag V. See the “Instruction Set Description” for detailed information.
• Bit 3 – V: Two’s Complement Overflow Flag
The Two’s Complement Overflow Flag V supports two’s complement arithmetics. See the
“Instruction Set Description” for detailed information.
• Bit 2 – N: Negative Flag
The Negative Flag N indicates a negative result in an arithmetic or logic operation. See the
“Instruction Set Description” for detailed information.
• Bit 1 – Z: Zero Flag
The Zero Flag Z indicates a zero result in an arithmetic or logic operation. See the “Instruction
Set Description” for detailed information.
• Bit 0 – C: Carry Flag
The Carry Flag C indicates a carry in an arithmetic or logic operation. See the “Instruction Set
Description” for detailed information.
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 on page 12 shows the structure of the 32 general purpose working registers in the
CPU.
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ATmega128
Figure 4. AVR CPU General Purpose Working Registers
General
Purpose
Working
Registers
70
R0
R1
R2
R13
R14
R15
R16
R17
R26
R27
R28
R29
R30
R31
Addr.
$00
$01
$02
$0D
$0E
$0F
$10
$11
$1A
$1B
$1C
$1D
$1E
$1F
X-register Low Byte
X-register High Byte
Y-register Low Byte
Y-register High Byte
Z-register Low Byte
Z-register High Byte
Most of the instructions operating on the Register file have direct access to all registers, and
most of them are single cycle instructions.
As shown in Figure 4, each register is also assigned a data memory address, mapping them
directly into the first 32 locations of the user Data Space. Although not being physically imple-
mented as SRAM locations, this memory organization provides great flexibility in access of the
registers, as the X-, Y-, and Z-pointer Registers can be set to index any register in the file.
X-register, Y-register,
and Z-register
The registers R26..R31 have some added functions to their general purpose usage. These reg-
isters are 16-bit address pointers for indirect addressing of the Data Space. The three indirect
address registers X, Y, and Z are described in Figure 5.
Figure 5. The X-, Y-, and Z-registers
X - register
15
7
R27 ($1B)
XH
07
R26 ($1A)
XL
0
0
Y - register
15
7
R29 ($1D)
YH
07
R28 ($1C)
YL
0
0
Z - register
15
7
R31 ($1F)
ZH
07
R30 ($1E)
ZL
0
0
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).
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Stack Pointer
The Stack is mainly used for storing temporary data, for storing local variables and for storing
return addresses after interrupts and subroutine calls. The Stack Pointer Register always points
to the top of the Stack. Note that the Stack is implemented as growing from higher memory loca-
tions to lower memory locations. This implies that a Stack PUSH command decreases the Stack
Pointer.
The Stack Pointer points to the data SRAM stack area where the Subroutine and Interrupt
Stacks are located. This Stack space in the data SRAM must be defined by the program before
any subroutine calls are executed or interrupts are enabled. The Stack Pointer must be set to
point above $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 implementa-
tions of the AVR architecture is so small that only SPL is needed. In this case, the SPH Register
will not be present.
Bit
15 14 13 12 11 10
9
8
SP15
SP14
SP13
SP12
SP11
SP10
SP9
SP8
SPH
SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 SPL
76543210
Read/Write
R/W R/W R/W R/W R/W R/W R/W R/W
R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value
0
0
0
0
0
0
0
0
00000000
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..1 – 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 0 – 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:
RAMPZ0 = 1:
Program memory address $0000 - $7FFF (lower 64 Kbytes) is
accessed by ELPM/SPM
Program memory address $8000 - $FFFF (higher 64 Kbytes) is
accessed by ELPM/SPM
Note that LPM is not affected by the RAMPZ setting.
Instruction
Execution Timing
This section describes the general access timing concepts for instruction execution. The AVR
CPU is driven by the CPU clock clkCPU, directly generated from the selected clock source for the
chip. No internal clock division is used.
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ATmega128
Figure 6 shows the parallel instruction fetches and instruction executions enabled by the Har-
vard architecture and the fast-access Register file concept. This is the basic pipelining concept
to obtain up to 1 MIPS per MHz with the corresponding unique results for functions per cost,
functions per clocks, and functions per power-unit.
Figure 6. The Parallel Instruction Fetches and Instruction Executions
T1 T2 T3
T4
clkCPU
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 destina-
tion register.
Figure 7. Single Cycle ALU Operation
T1
T2 T3
T4
clkCPU
Total Execution Time
Register Operands Fetch
ALU Operation Execute
Result Write Back
Reset and
Interrupt Handling
The AVR provides several different interrupt sources. These interrupts and the separate reset
vector each have a separate program vector in the program memory space. All interrupts are
assigned individual enable bits which must be written logic one together with the Global Interrupt
Enable bit in the Status Register in order to enable the interrupt. Depending on the Program
Counter value, interrupts may be automatically disabled when Boot Lock bits BLB02 or BLB12
are programmed. This feature improves software security. See the section “Memory Program-
ming” on page 286 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 59. 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 59 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
273.
When an interrupt occurs, the Global Interrupt Enable I-bit is cleared and all interrupts are dis-
abled. The user software can write logic one to the I-bit to enable nested interrupts. All enabled
interrupts can then interrupt the current interrupt routine. The I-bit is automatically set when a
Return from Interrupt instruction – RETI – is executed.
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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 inter-
rupt 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 */
__disable_interrupt();
EECR |= (1<<EEMWE); /* start EEPROM write */
EECR |= (1<<EEWE);
SREG = cSREG; /* restore SREG value (I-bit) */
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ATmega128
Interrupt Response
Time
When using the SEI instruction to enable interrupts, the instruction following SEI will be exe-
cuted before any pending interrupts, as shown in this example.
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
__enable_interrupt(); /* set global interrupt enable */
__sleep(); /* enter sleep, waiting for interrupt */
/* note: will enter sleep before any pending interrupt(s) */
The interrupt execution response for all the enabled AVR interrupts is four clock cycles mini-
mum. After four clock cycles, the program vector address for the actual interrupt handling routine
is executed. During this 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 three clock cycles. If
an interrupt occurs during execution of a multi-cycle instruction, this instruction is completed
before the interrupt is served. If an interrupt occurs when the MCU is in Sleep mode, the inter-
rupt execution response time is increased by four clock cycles. This increase comes in addition
to the start-up time from the selected sleep mode.
A return from an interrupt handling routine takes four clock cycles. During these 4-clock cycles,
the Program Counter (two bytes) is popped back from the Stack, the Stack Pointer is incre-
mented by two, and the I-bit in SREG is set.
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ATmega128
AVR
ATmega128
Memories
This section describes the different memories in the Atmel® AVR® ATmega128. The AVR archi-
tecture 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 128Kbytes 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 10,000 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 “Boot Loader Support – Read-While-Write Self-Programming” on page
273. “Memory Programming” on page 286 contains a detailed description on Flash programming
in SPI, JTAG, or Parallel Programming mode.
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 “Instruction Execution Tim-
ing” on page 13.
Figure 8. Program Memory Map
Program Memory
$0000
Application Flash Section
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Boot Flash Section
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SRAM Data
Memory
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ATmega128
The Atmel® AVR® ATmega128 supports two different configurations for the SRAM data memory
as listed in Table 1.
Table 1. Memory Configurations
Configuration
Internal SRAM Data Memory External SRAM Data Memory
Normal mode
ATmega103 Compatibility
mode
4096
4000
up to 64K
up to 64K
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 com-
patibility 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 Reg-
ister 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 inter-
nal 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
occupies the lowest 4352bytes in normal mode, and the lowest 4096bytes in the ATmega103
compatibility mode (Extended I/O not present), so when using 64Kbyte (65536 bytes) of Exter-
nal Memory, 61184bytes of External Memory are available in normal mode, and 61440 bytes in
ATmega103 compatibility mode. See “External Memory Interface” on page 25 for details on how
to take advantage of the external memory map.
When the addresses accessing the SRAM memory space exceeds the internal data memory
locations, the external data SRAM is accessed using the same instructions as for the internal
data memory access. When the internal data memories are accessed, the read and write strobe
pins (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 two-byte 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. Interrupts, subroutine calls and returns will need five, seven, or nine clock cycles
more than specified in the instruction set manual for one, two, and three wait-states.
The five different addressing modes for the data memory cover: Direct, Indirect with Displace-
ment, Indirect, Indirect with Pre-decrement, and Indirect with Post-increment. In the Register file,
registers R26 to R31 feature the indirect addressing pointer registers.
The direct addressing reaches the entire data space.
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The Indirect with Displacement mode reaches 63 address locations from the base address given
by the Y- or Z-register.
When using register indirect addressing modes with automatic pre-decrement and post-incre-
ment, the address registers X, Y, and Z are decremented or incremented.
The 32 general purpose working registers, 64 I/O registers, and the 4096bytes 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 11.
Figure 9. Data Memory Map
Memory Configuration A
Memory Configuration B
Data Memory
32 Registers
64 I/O Registers
160 Ext I/O Reg.
Internal SRAM
(4096 x 8)
$0000 - $001F
$0020 - $005F
$0060 - $00FF
$0100
$10FF
$1100
External SRAM
(0 - 64K x 8)
Data Memory
32 Registers
64 I/O Registers
Internal SRAM
(4000 x 8)
$0000 - $001F
$0020 - $005F
$0060
$0FFF
$1000
External SRAM
(0 - 64K x 8)
$FFFF
$FFFF
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ATmega128
Data Memory Access
Times
This section describes the general access timing concepts for internal memory access. The
internal data SRAM access is performed in two clkCPU cycles as described in Figure 10.
Figure 10. On-chip Data SRAM Access Cycles
T1 T2
T3
clk
CPU
Address
Data
WR
Data
RD
Compute Address
Address valid
Memory access instruction
Next instruction
EEPROM Data
Memory
The Atmel® AVR®ATmega128 contains 4Kbytes of data EEPROM memory. It is organized as a
separate data space, in which single bytes can be read and written. The EEPROM has an
endurance of at least 100,000 write/erase cycles. The access between the EEPROM and the
CPU is described in the following, specifying the EEPROM Address Registers, the EEPROM
Data Register, and the EEPROM Control Register.
“Memory Programming” on page 286 contains a detailed description on EEPROM programming
in SPI, JTAG, or Parallel Programming mode
EEPROM Read/Write
Access
The EEPROM access registers are accessible in the I/O space.
The write access time for the EEPROM is given in Table 2. A self-timing function, however, lets
the user software detect when the next byte can be written. If the user code contains instructions
that write the EEPROM, some precautions must be taken. In heavily filtered power supplies, VCC
is likely to rise or fall slowly on Power-up/down. This causes the device for some period of time
to run at a voltage lower than specified as minimum for the clock frequency used. See “Prevent-
ing EEPROM Corruption” on page 24. for details on how to avoid problems in these situations.
In order to prevent unintentional EEPROM writes, a specific write procedure must be followed.
Refer to the description of the EEPROM Control Register for details on this.
When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction is
executed. When the EEPROM is written, the CPU is halted for two clock cycles before the next
instruction is executed.
EEPROM Address
Register – EEARH and
EEARL
Bit
Read/Write
Initial Value
15
EEAR7
7
R
R/W
0
X
14
EEAR6
6
R
R/W
0
X
13
EEAR5
5
R
R/W
0
X
12
EEAR4
4
R
R/W
0
X
11
EEAR11
EEAR3
3
R/W
R/W
X
X
10
EEAR10
EEAR2
2
R/W
R/W
X
X
9
EEAR9
EEAR1
1
R/W
R/W
X
X
8
EEAR8
EEAR0
0
R/W
R/W
X
X
EEARH
EEARL
• 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.
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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 4
Kbytes 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 7 6 5 4 3 2 1 0
MSB
LSB
EEDR
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
• 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 7 6 5 4 3 2 1 0
EERIE EEMWE EEWE EERE
EECR
Read/Write
R
R
R
R
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
X
0
• 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 inter-
rupt when EEWE is cleared.
• Bit 2 – EEMWE: EEPROM Master Write Enable
The EEMWE bit determines whether setting EEWE to one causes the EEPROM to be written.
When EEMWE is written to one, writing EEWE to one within four 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 SPMCSR 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.
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The EEPROM can not be programmed during a CPU write to the Flash memory. The software
must check that the Flash programming is completed before initiating a new EEPROM write.
Step 2 is only relevant if the software contains a boot loader allowing the CPU to program the
Flash. If the Flash is never being updated by the CPU, step 2 can be omitted. See “Boot Loader
Support – Read-While-Write Self-Programming” on page 273 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 four last steps to avoid these problems.
When the write access time has elapsed, the EEWE bit is cleared by hardware. The user soft-
ware can poll this bit and wait for a zero before writing the next byte. When EEWE has been set,
the CPU is halted for two cycles before the next instruction is executed.
• Bit 0 – EERE: EEPROM Read Enable
The EEPROM Read Enable Signal EERE is the read strobe to the EEPROM. When the correct
address is set up in the EEAR Register, the EERE bit must be written to a logic one to trigger the
EEPROM read. The EEPROM read access takes one instruction, and the requested data is
available immediately. When the EEPROM is read, the CPU is halted for four cycles before the
next instruction is executed.
The user should poll the EEWE bit before starting the read operation. If a write operation is in
progress, it is neither possible to read the EEPROM, nor to change the EEAR Register.
The calibrated Oscillator is used to time the EEPROM accesses. Table 2 lists the typical pro-
gramming time for EEPROM access from the CPU.
Table 2. EEPROM Programming Time
Symbol
Number of Calibrated RC
Oscillator Cycles(1)
Typ Programming Time
EEPROM Write (from CPU)
8448
Note: 1. Uses 1MHz clock, independent of CKSEL-fuse settings.
8.5ms
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The following code examples show one assembly and one C function for writing to the
EEPROM. The examples assume that interrupts are controlled (for example, by disabling inter-
rupts globally) so that no interrupts will occur during execution of these functions. The examples
also assume that no flash boot loader is present in the software. If such code is present, the
EEPROM write function must also wait for any ongoing SPM command to finish.
Assembly Code Example
EEPROM_write:
; Wait for completion of previous write
sbic EECR,EEWE
rjmp EEPROM_write
; Set up address (r18:r17) in address register
out EEARH, r18
out EEARL, r17
; Write data (r16) to data register
out EEDR,r16
; Write logical one to EEMWE
sbi EECR,EEMWE
; Start eeprom write by setting EEWE
sbi EECR,EEWE
ret
C Code Example
void EEPROM_write(unsigned int uiAddress, unsigned char ucData)
{
/* Wait for completion of previous write */
while(EECR & (1<<EEWE))
;
/* Set up address and data registers */
EEAR = uiAddress;
EEDR = ucData;
/* Write logical one to EEMWE */
EECR |= (1<<EEMWE);
/* Start eeprom write by setting EEWE */
EECR |= (1<<EEWE);
}
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The next code examples show assembly and C functions for reading the EEPROM. The exam-
ples assume that interrupts are controlled so that no interrupts will occur during execution of
these functions.
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;
}
EEPROM Write During
Power-down Sleep
Mode
When entering Power-down sleep mode while an EEPROM write operation is active, the
EEPROM write operation will continue, and will complete before the write access time has
passed. However, when the write operation is completed, the Oscillator continues running, and
as a consequence, the device does not enter Power-down entirely. It is therefore recommended
to verify that the EEPROM write operation is completed before entering Power-down.
Preventing EEPROM
Corruption
During periods of low VCC, the EEPROM data can be corrupted because the supply voltage is
too low for the CPU and the EEPROM to operate properly. These issues are the same as for
board level systems using EEPROM, and the same design solutions should be applied.
An EEPROM data corruption can be caused by two situations when the voltage is too low. First,
a regular write sequence to the EEPROM requires a minimum voltage to operate correctly. Sec-
ondly, the CPU itself can execute instructions incorrectly, if the supply voltage is too low.
EEPROM data corruption can easily be avoided by following this design recommendation:
Keep the AVR RESET active (low) during periods of insufficient power supply voltage. This can
be done by enabling the internal Brown-out Detector (BOD). If a reset occurs while a write oper-
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ATmega128
I/O Memory
External Memory
Interface
Overview
ation is in progress, the write operation will be completed provided that the power supply voltage
is sufficient.
The I/O space definition of the ATmega128 is shown in “Register Summary” on page 362.
All Atmel® AVR®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 section 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.
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).
When the eXternal MEMory (XMEM) is enabled, address space outside the internal SRAM
becomes available using the dedicated External Memory pins (see Figure 1 on page 2, Table 27
on page 72, Table 33 on page 76, and Table 45 on page 84). The memory configuration is
shown in Figure 11.
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ATmega128
Figure 11. External Memory with Sector Select
Memory Configuration A
0x0000
Memory Configuration B
0x0000
Internal memory
Lower sector
SRW01
SRW00
0x10FF
0x1100
Internal memory
0x0FFF
0x1000
External Memory
(0-60K x 8)
Upper sector
SRL[2..0]
External Memory
(0-60K x 8)
SRW10
SRW11
SRW10
ATmega103
Compatibility
Using the External
Memory Interface
0xFFFF
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)
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.
• RD, WR and ALE pins are output only (Port G in ATmega128).
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.
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Address Latch
Requirements
ATmega128
The control bits for the External Memory Interface are located in three registers, the MCU Con-
trol 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 “I/O Ports” on page 65. The XMEM
interface will auto-detect whether an access is internal or external. If the access is external, the
XMEM interface will output address, data, and the control signals on the ports according to Fig-
ure 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 inter-
face 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.
Due to the high-speed operation of the XRAM interface, the address latch must be selected with
care for system frequencies above 8MHz @ 4V and 4MHz @ 2.7V. When operating at condi-
tions above these frequencies, the typical old style 74HC series latch becomes inadequate. The
External Memory Interface is designed in compliance to the 74AHC series latch. However, most
latches can be used as long they comply with the main timing parameters. The main parameters
for the address latch are:
• D to Q propagation delay (tPD).
• Data setup time before G low (tSU).
• Data (address) hold time after G low (TH).
The External Memory Interface is designed to guaranty minimum address hold time after G is
asserted low of th = 5 ns. Refer to tLAXX_LD/tLLAXX_ST in “External Data Memory Timing” Tables
137 through Tables 144 on pages 328 - 330. The D-to-Q propagation delay (tPD) must be taken
into consideration when calculating the access time requirement of the external component. The
data setup time before G low (tSU) must not exceed address valid to ALE low (tAVLLC) minus PCB
wiring delay (dependent on the capacitive load).
Figure 12. External SRAM Connected to the AVR
AD7:0
ALE
AVR
A15:8
RD
WR
DQ
G
D[7:0]
A[7:0]
SRAM
A[15:8]
RD
WR
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Pull-up and Bus-
keeper
Timing
ATmega128
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.
The XMEM interface also provides a bus-keeper on the AD7:0 lines. The bus-keeper can be dis-
abled and enabled in software as described in “External Memory Control Register B – XMCRB”
on page 32. When enabled, the bus-keeper will ensure a defined logic level (zero or one) on the
AD7:0 bus when these lines would otherwise be tri-stated by the XMEM interface.
External Memory devices have different timing requirements. To meet these requirements, the
ATmega128 XMEM interface provides four different wait-states as shown in Table 4. It is impor-
tant to consider the timing specification of the External Memory device before selecting the wait-
state. The most important parameters are the access time for the external memory 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 tLLRL+ tRLRH - tDVRH in Tables 137
through Tables 144 on pages 328 - 330). The different wait-states are set up in software. As an
additional feature, it is possible to divide the external memory space in two sectors with individ-
ual 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 Table 137 to Table 144 and Figure 157 to Figure 160 in the “External Data Mem-
ory Timing” on page 328.
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). Conse-
quently, the XMEM interface is not suited for synchronous operation.
Figure 13. External Data Memory Cycles without Wait-state (SRWn1=0 and SRWn0=0)
T1 T2 T3 T4
System Clock (CLKCPU)
ALE
A15:8 Prev. addr.
Address
DA7:0 Prev. data
Address XX
Data
WR
DA7:0 (XMBK = 0) Prev. data
Address
Data
DA7:0 (XMBK = 1) Prev. data
Address XXXXX
Data
XXXXXXXX
RD
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).
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ATmega128
Figure 14. External Data Memory Cycles with SRWn1 = 0 and SRWn0 = 1(1)
T1 T2 T3 T4
System Clock (CLKCPU)
T5
ALE
A15:8 Prev. addr.
Address
DA7:0 Prev. data
Address XX
Data
WR
DA7:0 (XMBK = 0) Prev. data
Address
Data
DA7:0 (XMBK = 1) Prev. data
Address
Data
RD
Note:
1. SRWn1 = SRW11 (upper sector) or SRW01 (lower sector), SRWn0 = SRW10 (upper sector) or
SRW00 (lower sector).
The ALE pulse in period T5 is only present if the next instruction accesses the RAM (internal
or external).
Figure 15. External Data Memory Cycles with SRWn1 = 1 and SRWn0 = 0(1)
T1
T2
T3 T4
T5
System Clock (CLKCPU)
T6
ALE
A15:8 Prev. addr.
Address
DA7:0 Prev. data
Address XX
Data
WR
DA7:0 (XMBK = 0) Prev. data
Address
Data
DA7:0 (XMBK = 1) Prev. data
Address
Data
RD
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).
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ATmega128
Figure 16. External Data Memory Cycles with SRWn1 = 1 and SRWn0 = 1(1)
T1
T2
T3 T4
T5
System Clock (CLKCPU)
ALE
T6
A15:8 Prev. addr.
Address
DA7:0 Prev. data
Address XX
Data
WR
DA7:0 (XMBK = 0) Prev. data
Address
Data
DA7:0 (XMBK = 1) Prev. data
Address
Data
RD
T7
Note:
1. SRWn1 = SRW11 (upper sector) or SRW01 (lower sector), SRWn0 = SRW10 (upper sector) or
SRW00 (lower sector).
The ALE pulse in period T7 is only present if the next instruction accesses the RAM (internal
or external).
XMEM Register
Description
MCU Control Register
– MCUCR
Bit
Read/Write
Initial Value
7
SRE
R/W
0
6
SRW10
R/W
0
5
SE
R/W
0
4
SM1
R/W
0
3
SM0
R/W
0
2
SM2
R/W
0
1
IVSEL
R/W
0
0
IVCE
R/W
0
MCUCR
• Bit 7 – SRE: External SRAM/XMEM Enable
Writing SRE to one enables the External Memory Interface.The pin functions AD7:0, A15:8,
ALE, WR, and RD are activated as the alternate pin functions. The SRE bit overrides any pin
direction settings in the respective data direction registers. Writing SRE to zero, disables the
External Memory Interface and the normal pin and data direction settings are used.
• Bit 6 – SRW10: Wait-state Select Bit
For a detailed description 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
Figure 14.
External Memory
Control Register A –
XMCRA
Bit
Read/Write
Initial Value
76543210
SRL2
SRL1
SRL0 SRW01 SRW00 SRW11
XMCRA
R
R/W
R/W
R/W
R/W
R/W
R/W
R
00000000
• 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.
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