Wednesday, June 29, 2011

Draw the pin-out diagram of 82C55A PPI. How many modes you can select on 82C55A PPI? Explain.

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


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