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