Assembly program to transfer the status of switches

Problem – Write an assembly language program in 8085 of interfacing between 8085 and 8255. 8 switches are connected at port A. Transfer the status of these switches into port B where LEDs are connected.

Example –

Input port is A and output port is B.

Algorithm –

  1. Construct the control word register
  2. Input the data from port A
  3. Display the result in port B

Program –

Mnemonics Comments
MVI A, 90 A ← 92
OUT 83 Control Register ← A
IN 80 A → Port A;
OUT 81 Port C A ← A
RET Return

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=0as Port B is displaying the result
  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. OUT 81 displaying the result in 81H which is the port number of port B.
  5. RET return

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