ATMEGA644-20AU Datasheet PDF - Microchip

The ATMEGA644-20AU is a 8-bit high-performance, low-power AVR RISC-based Microcontroller Unit combines 64kB ISP flash memory with read-while-write capabilities, 2kB EEPROM, 4kB SRAM, 32 general purpose I/O lines, 32 general purpose working registers, real time counter, three flexible timer/counters with compare modes and PWM, 2 USARTs, byte oriented 2-wire serial interface, 8-channel/10-bit A/D converter with optional differential input stage with programmable gain, programmable watchdog timer with internal oscillator, SPI serial port, JTAG test interface for on-chip debugging and six software selectable power saving modes. All the 32 registers are directly connected to the Arithmetic Logic Unit, 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.