The basic AVR feature set of the ATmega128RFA1 is derived from the
ATmega1281/2561. Address locations and names of the implemented modules and
registers are unchanged as long as it fits the target application of a very small and
power efficient radio system. In addition, several new features were added.
Backward compatibility of the ATmega128RFA1 to the ATmega1281/2561 is provided
in most cases. However some incompatibilities between the microcontrollers exist.