hi,
I use port 0,port 1 and port3 as input port, and port 2 as output port.
when i simulate the program with 8052 simulator, it works fine. the truoble appears when i put the code to at89c51.the mcu seems "shaking" (every pin include the supply line) when i plug the input (at port0).all the input comes from ttl circuit the initial logic is 0. could anybody please tell me why this is happen?

best regard
ridvvan