The ATMEGA644PA-AUR is an 8-bit AVR microcontroller from Microchip in TQFP-44, running at 20MHz with 64KB Flash, 4KB SRAM, and 2KB EEPROM. The -PA suffix indicates picoPower technology: the device draws 0.1uA in power-save mode and 0.5uA in power-down mode, 10x lower than the original ATMEGA644P. The 64KB Flash supports 10,000 write/erase cycles with 20-year data retention. The 10-bit ADC has 8 channels with 15ksps and auto-trigger from timer events. Two 8-bit timers (Timer0, Timer2) and one 16-bit timer (Timer1) provide 6 channels of PWM, input capture, and real-time clock. The USART supports serial at up to 2Mbps with framing error detection. The SPI port runs at up to 10MHz in master mode. The I2C/TWI interface supports 400kHz. The JTAG interface provides in-circuit debugging and boundary-scan testing. The device includes: analog comparator, watchdog timer, brown-out detection (programmable at 1.8V/2.7V/4.3V), and on-chip calibrated RC oscillator (8MHz +/-10%). The picoPower features include: clock prescaler for reducing power during low-activity periods, interrupt-driven wake-up from all sleep modes, and ADC noise reduction mode (sleeps CPU during ADC conversion). The -AUR suffix specifies TQFP-44, industrial temperature (-40C to +85C). The ATMEGA644PA is popular in Arduino Mega-compatible designs and industrial control applications requiring 64KB Flash.