8085 program to exchange content of HL register pair with DE register pair
Problem – Write an assembly language program in 8085 microprocessor to exchange content of HL register pair with DE register pair using PUSH and POP instructions.
Example –
Assumption – Content is already present in HL and DE register.
Algorithm –
- Initialize stack pointer (SP) by 3FFF.
- Push the content of H and L register into the stack. Decrements SP by 2.
- Push the content of D and E register into the stack. Decrements SP by 2.
- Pop the upper two bytes from top of stack and place it in HL register. Increment SP by 2.
- Pop the remaining two bytes from top of stack and place it in DE register. Increment SP by 2.
Program –
| MEMORY ADDRESS | MNEMONICS | COMMENT |
|---|---|---|
| 2000 | LXI SP 3FFF | SP <- 3FFF |
| 2003 | PUSH H | SP <- SP – 1, M[SP] <- H, SP <- SP – 1, M[SP] <- L |
| 2004 | PUSH D | SP <- SP – 1, M[SP] <- D, SP <- SP – 1, M[SP] <- E |
| 2005 | POP H | L <- M[SP], SP <- SP + 1, H <- M[SP], SP <- SP + 1 |
| 2006 | POP D | E <- M[SP], SP <- SP + 1, D <- M[SP], SP <- SP + 1 |
| 2007 | HLT | ENDT |
Explanation – Registers used H, L, D, E:
- LXI SP 3FFF: initialize SP by 3FFF.
- PUSH H: push the content of H and L register into the stack and decrements stack pointer by 2.
- PUSH D: push the content of D and E register into the stack and decrements stack pointer by 2.
- POP H: pop the upper two bytes from top of stack and place it in HL register pair and increment SP by 2.
- POP D: pop the upper two bytes from top of stack and place it in DE register pair and increment SP by 2.
- HLT: stops executing the program and halts any further execution.
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