For more I/O you can use the AT89S8252 (32 I/O) in DIP-40 case, which can be programmed on board.

I/O expansion can easy be done with standard CMOS/TTL circuits, e.g.:

8 outputs: 74HC595 or CD4094

8 inputs: 74HC165 or CD4021

Also some LED displays have build in drivers and can be controlled over only 2 wire, e.g. TSM6755 (4 digits).


With 2 TSM6755 you have an 8 digit display on 2 wire. And with the MAX127 on also 2 wire you have remaining 28 I/O free on the AT89S8252.


Peter