Replacing At90s4433 By Atmega48

 This application note is a guide to assist current AT90S4433 users in converting
existing designs to ATmega48. ATMEGA48 is not designed to be a replacement for
AT90S4433 but is pin compatible and has a very similar feature set.
ATMEGA48 contains more SRAM memory  than AT90S4433 and it has additional
peripheral modules and features. However with a few modifications to the I/O
register access, ATMEGA48 CAN replace AT90S4433 on existing circuit boards. In
addition to the functional changes, the electrical characteristics of the ATMEGA48
are different, including an increase in operating frequency ranges. Check the
datasheet for detailed information.
Improvements and added features in ATMEGA48 that are not in conflict with those
in AT90S4433 are not covered by the scope of this document. Throughout this
document it is assumed that ATMEGA48 factory-default settings are used unless
otherwise noted.