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Interface 8255 with 8085 microprocessor for addition
• Last Updated : 04 May, 2020

Problem – Interface 8255 with 8085 microprocessor and write an assembly program that determines the addition of contents of port A and port B and store the result in port C.

Example –  Algorithm –

1. Construct the control word register
2. Input the data from port A and port B
3. Add the contents of port A and port B
4. Display the result in port C

Program –

MVI A, 90A ← 92
OUT 83Control Register ← A
IN 80A ← Port A;
MOV B, AB ← A;
IN 81A ← Port B;
ADD BA ← A+B;OUT 82Port C ← A
RETReturn

Explanation –

1. MVI A, 92 means that the value of control register is 92.
```D7=1 as it is in I/O mode.
D6=0 & D5=0 as Poet A is in m0 mode.
D4=1 as Port A is taking input.
D3=0 & D0=0 as Port C is not taking part.
D2=0 as mode of Port B is m0.
D1=1as Port B is taking the input.```
2. OUT 83 putting the value of A in 83H which is the port number of port control register.
3. IN 80 taking input from 80H which is the port number of port A.
4. MOV B, A copies the content of A register to B register.
5. IN 81 take input feom 81H which is the port number of port B.
6. ADD B add the contents of A register and B register.
7. OUT 82 displaying the result in 81H which is the port number of port C.
8. RET return
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