PA0- PA7: port a, it is 8 bit bi-directional i/o pins.

PB0-PB7: port b, It is 8 bit bi-directional i/o pins.

PC0-PC7: port c, It is also a bi-directional i/o pins. It is divided in two sections: PC0-PC3 and PC4-PC7. These two section can be used to transfer 4 bit data.

D0-D7: data pins for data transfer

RESET: reset input, It is used to reset 8255 ic.

RD-bar: read input, it is used to coordination with other signals to send data through data lines.

WR-bar: write input, used in coordination with other signals to send data to 8255.

A1-A0: address pins

00-Port A
01-Port B
10-Port C
11-Control Reigster

CS-bar: chip select

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