What are the different modes in which 8255 Programmable Peripheral Interface (PPI) can operate?
- Twenty Four I/O lines in 38-bit port groups - A, B and C
- A and B can be 8-bit input/output ports
- C can serve as twenty four-bit input /output ports
- 3 modes of operation:
- Mode 0: A, B, C simple input / output level sensitive ports
- Mode 1: A, B input / output ports along with strobe control in C
- Mode 2: A is bidirectional along with control/handshake in B and C
- A, B can only modify 1 byte at a time
- C has individual bit set/reset ability
- Improvement is non-dedicated circuit can change port configuration along with software and no "glue logic"
- Ports A, B and C are utilized for I/O data.
- The control register is programmed to choose the operation mode of the three ports A, B and C.
- Mode 0: simple I/O mode
- Any of the ports A, B, CL and CU can be programmed as input / output.
- No control of individual bits (all bits are out or in