Ports A, B, and C:
The 8255 have three 8-bit ports (A, B, and C). All of can be configured to a wide variety of functional characteristics by the system software but each has its own special features or "personality" to further enhance the power and flexibility of the 8255.
- Port A One 8-bit data input latch and one 8-bit data output latch/buffer. "Pull- up" and "pull-down" both of bus-hold devices are exists on Port A.
- Port B One 8-bit data input buffer and one 8-bit data input/output latch/buffer.
- Port C One 8-bit data output latch/buffer and one 8-bit data input buffer (no latch for input). This port might be divided into two 4-bit ports under the mode control.
Each 4-bit port contains 4-bit latch and it can be utilized for the control signal output and status signal inputs in conjunction with ports A and B.
Figure: Block Diagram of the 8255 Programmable Peripheral Interface (PPI)