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 –
- Construct the control word register
- Input the data from port A
- 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 –
- 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
- OUT 83 putting the value 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.
- OUT 81 displaying the result in 81H which is the port number of port B.
- RET return
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