Explain in detail the operation of 8255 in mode1 taking suitable example.

In mode1, Ports A and B are programmed as input or output ports and Port C is used for handshaking.

8255 handshaking

PPI Interface to CPU

Port A and or port B treated as latching input devices. External data is stored into the ports till the microprocessor is ready.

Port C is utilized for control or handshaking signal that cannot for data.

Signal Definitions for Mode 1 Strobed Input.

STB‾: The strobe input loads data in port latch on a 0 to 1 transition,

IFB: Input buffer full is an output specifying that input latch has information.

INTR: Interrupt requests outputs which request an interrupt.

 INTE: Interrupt enable signal is neither output nor an input; this is an internal bit programmed through the PC4 that is port A to PC2 that is port B bits.

PC7, PC6: The port C pins 7 and 6 both are general purpose I/O pins which are available for any reasons.