Pin-Out Diagram of 82C55A:
I/O Ports: It has three I/O ports, A, B and C. Each of these has 8 pins.
CS : This is used to select the 82C55A for programming and reading or writing.
A0 & A1: Register selection is done using the A0 and A1, which select an internal register for programming or operation. Following given table shows those arrangements,
|
A0
|
A1
|
Function
|
|
0
|
0
|
Port A
|
|
0
|
1
|
Port B
|
|
1
|
0
|
Port C
|
|
1
|
1
|
Command Register
|
Groups: The total 24 pins of the 3 ports has been grouped into two groups, Group A contains Port A and the upper half portion of Port C (PC7 – PC4) and Group B contains Port B and the lower half portion of the Port C (PC3 – PC0).
RESET: This is used to initialize the 82C55A to mode 0 where all the three ports will be used as input. This is used to prevent damage.
Selectable Modes: We can select three modes in 82C55A, those are as follows,
Mode 0 : PA, PB and PC; all as I/O
Mode 1 : PA and PB as I/O and PC and control
Mode 2 : PA as bidirectional, PC as control and PB has no use