I regards to aka j's reply, I was thinking along the same lines. As long as i never go above the 16k point in ram or eprom, then i should not have a problem. I have a system which has a bit banged serial port currently using p3.0 and p3.1. I need to use this pins for a real serial UART. So i needed to come up with a way to get two more output pins. Originally i was going to use a little AVR chip to pull 8 bits of the the main board thru an extra port on a 8255. This is a good solution, cause it is faster than bit banging with the 8051, allowing the 8051 to do other things, while the AVR chip did the work. But that involves using another chip. So then i realized that i might be able to limit my ram access, and steal those pins. But as Peter says, I guess everytime i use MOVX, i will be writting zeros to these pins, no matter what. So i guess this is up in the air. I would like to move to a chip with more ports, but don't want to spend the money. If i did move to another chip, does anyone have any suggestions? I'm using a Dallas 80C320 right now, so it needs to be fast. Thanks.