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 Programma-
ble 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 Two-wire Serial Interface, an 8-channel, 10-bit ADC with optional differential
input stage with programmable gain, programmable Watchdog Timer with Internal Oscil-
lator, 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 asyn-
chronous 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 Asynchro-
nous Timer continue to run.
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. Soft-
ware 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.
ATmega103 and
ATmega128
Compatibility
The ATmega128 is a highly complex microcontroller where the number of I/O locations
supersedes the 64 I/O locations reserved in the AVR instruction set. To ensure back-
ward 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 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 vec-
tors are removed.
4
ATmega128
2467OS–AVR–10/06
ATMEL [ ATMEL CORPORATION ]
