ATmega64/128 Datasheet, Pinout, Minimal Circuit, Maximum Frequency Calculator

The ATmega64/128 are larger at 64-pins than most other AVR devices, but that is because they not only have an external memory interface, but I/O that can be used at the same time. There are 2 other ATmega's with external memory interfaces, but both are 40-pin, and most of the I/O is used by the memory bus.

The ATmega64/128 have an external memory bus for interfacing with up to 64k of memory. There are two 8-bit timers, and two 16-bit, as well as two USARTS. The ISP programming port on these parts is a "dedicated" SPI port for programming, but it shares SCK with the other SPI port.

Power Supply vs. Maximum Frequency

The ATmega64/128 are specified at a power supply voltage of 4.5V to 5.5V, 16MHz maximum frequency. The -L parts are rated 8MHz from 2.7V to 5.5V. The calculator below will help determine the frequency you can run with a given power supply voltage.

Maximum Frequency Calculator for ATmega64/128

ATmega64/128 Features
Flash 64k128k
RAM 2k4k
I/O Pins 53
Interrupts 35
ADC Channels 8
RT Counter 1
Timers (8-bit) 2
Timers (16-bit) 2
PWM (8-bit) 2
PWM (16-bit) 4
Price (1's) $12.10$17.61
Power Consumption (approximate) 2.0mA/MHz@5V
Maximum I/O Current (per pin) 40mA
Maximum I/O Current (all ports) unspecified
Maximum I/O Current (total)400mA (QFP/MLF)

ATmega64/128 Datasheet

Link to ATmega64 datasheet from Atmel's website.
Link to ATmega128 datasheet from Atmel's website.

ATmega128 Pinout

ATmega128 pinout
"Minimal" ATmega128 Schematic Diagram

This is a minimal ATmega128 circuit. A more complete system would have an external memory interface as well.

ATmega128 minimal schematic diagram