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
|MVI A, 90||A ← 92|
|OUT 83||Control Register ← A|
|IN 80||A → Port A;|
|OUT 81||Port C A ← A|
- 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
- The program is simple and straightforward, consisting of only two instructions.
- The program uses the input/output instruction to read the status of the switches, which is an efficient method.
- The program uses the store accumulator instruction to transfer the status of the switches to a memory location.
- The program can be easily modified to transfer the status of other input devices, such as sensors or buttons.
- The program assumes that the switches are connected to port 00H, and does not provide error checking for invalid input.
- The program assumes that the memory location 1000H is available for use and does not check for memory conflicts.
- The program does not provide any feedback to the user or the system to indicate that the transfer has been completed successfully.
- The program does not provide any error checking or recovery mechanisms in case of hardware or software failures.
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