This application note explains how to migrate designs from ATmega16/32 microcontrollers to ATmega164P/324P/644P devices.
The document provides a migration guide for engineers moving existing ATmega16 or ATmega32 designs to the newer ATmega164P, ATmega324P, or ATmega644P parts. It covers general porting considerations, memory differences, I/O mapping, EEPROM programming, external crystal requirements, register and bit‑name changes, fuse settings, interrupt vector changes, JTAG boundary‑scan updates, and operational voltage ranges.
Key differences highlighted include the extended I/O space, additional USART, higher maximum clock speed (up to 20 MHz), low‑voltage operation (down to 1.8 V for some variants), and the presence of four fuse bytes instead of two. The note also points to the respective datasheets for detailed electrical specifications and provides example crystal ESR requirements.