Abstract : The 8255 is a general purpose programmable I/O device designed for use with microprocessors to send 8 bit data from Microprocessor to I/O device and vice versa through interface modules known as ports . It has three 8-bit ports. These ports are called port A, port B ,port C. Thus in all ,there are 24(=8*3) bits available from these ports of 8255 .