I'm trying to interface a circuit through an 8255 PPI interface chip and then use a c program to manipulate the input. Once the circuit is interfaced to the PC how do I get the data into my c program
Look at the address decoding to activate the 8255's "CS" line. That decoding, plus the addresses of A0 and A1 will give you all 4 addresses of the chip. One of the addresses is a "control" register, the other 3 are the 3 ports.