Parallel Port Interface / Programmable Input Output(PPI / PIO )
One of the many chips that can be programmed port-The port is 8255 (PIO = Programmable Input Output). 8255 has 3 I / O ports (A, B, C), each port consists of 8 bits that can be programmed as input or output. Port 8255 is divided into two groups, group A consists of Port A and 4 high bits (upper bits) port C (C7, C6, C5 and C4). Port B consists of port B and the lower 4 bits (lower bits) port C (C3, C2, C1 and C0).carried out in groups rather than on each port. 8255 PIO can be programmed for three modes namely:
- Mode 0 (simple I / O)
- Mode 1 (handshake I / O)
- Mode 2 (double handshake I / O)
Parallel Port Interface Block Diagram 8255
To use ports 8255 first we must program the ports in accordance with the desired. Programming can be done by sending the bits of control bits (control word) the Control Word is the work of 8255 will determine whether the use mode 0, mode 1 or mode 2. In addition the control word is also used to set the third port if all three inputs, outputs or a combination of both.