Problem – Interface 8255 with 8085 microprocessor and write an assembly program which determine the addition of contents of port A and port B and store the result in port C.
Example –
Algorithm –
- Construct the control word register
- Input the data from port A and port B
- Add the contents of port A and port B
- Display the result in port C
Program –
Mnemonics | Comments |
---|---|
MVI A, 90 | A ← 92 |
OUT 83 | Control Register ← A |
IN 80 | A ← Port A; |
MOV B, A | B ← A; |
IN 81 | A ← Port B; |
ADD B | A ← A+B; |
OUT 82 | Port C ← A |
RET | Return |
Explanation –
- MVI A, 92 means that the value of control regidter 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.
- OUT 83 putting the vaue of A in 83H which is the port number of port control register.
- IN 80 taking input from 80H which is the port number of port A.
- MOV B, A copies the content of A register to B register.
- IN 81 take input feom 81H which is the port number of port B.
- ADD B add the contents of A register and B register.
- OUT 82 displaying the result in 81H which is the port number of port C.
- RET return
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