20 MHz 8-bit AVR with 64 KB Flash — what the memory map buys you
The 64 KB Flash (organized as 32K x 16) gives you room for a full control firmware stack — think motor-control loops, sensor fusion, or a Modbus slave — without needing external memory. The 4 KB SRAM handles moderate data buffers and stack depth; the 2 KB EEPROM stores calibration coefficients and configuration parameters that survive power cycles.
On-chip peripherals include an 8-channel 10-bit ADC, three PWM channels, brown-out detection, power-on reset, and a watchdog timer — enough to run a closed-loop control system without external supervisory ICs.
Microchip lists the ATMEGA644A-MU as an active product (ROHS3 compliant). The 44-VQFN package is a common footprint across the ATmega644A family, so a pin-compatible density upgrade (e.g., to the 128 KB variant) is possible without a board spin if firmware grows.
44-VQFN footprint and layout notes
The pad is electrically connected to ground (VSS) on the die, so the PCB landing pattern should match the 7x7 mm body with a central ground slug.