Interface 8255 with 8085 microprocessor for addition

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 –

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 –

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 –

1. 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.

2. OUT 83 putting the vaue 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