When i use external memory, port 0 and 2 will be used for data and addressing, so i'll be left with only the serial port and port 1. I open to suggestion on ways to add another two I/O ports. Thanks
Ricky, We found the Atmel ATF15XXASL series of CPLDs to work fine for our port expansions. I do suggest the "L" version for reducing your power requirement. We just used the Atmel ATF1502ASL for expansion on a 89C51 device...works great. Alan