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How can you control LEDs using microprocessor via 82C55A PPI? Draw the interface diagram & write the necessary assembly codes.

Controlling LEDs Using Microprocessor VIA 82C55A:

Using the 82C55A, we can control LED lights. We can use the pins of one port to connect with one leg of the LEDs and pins of another port to connect rest of the legs. Then we can program the 82C55A to control the LEDs. It can be done with a program like the one given below,

                   CONTROL  PROC                   NEAR
                                      MOV AL, 10000000B    ; creating format
                                      OUT  CR, AL                  ; setting command register
                                      MOV AL, 10101000B    ; sending 1 to LED0, LED2, LED4
                                      OUT PA, AL                 ; sending to port A
                                      MOV AL, 00000000B    ; sending 0 to LED0-LED7
                                      OUT  PB, AL                  ; sending to port B
                   CONTROL  ENDP

            Here first of all we are setting the command byte as A. Then we are sending 10101000 value to port A, in that way we are giving 1’s to LED0, LED2 and LED4. After that, sending 00000000 to port B. Now, those LED’s which has 1 at one leg and 0 at another will light up. So here, the LED0, LED1 and LED4 will light up.

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