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Access & Exchange Content of Flag Register F with Register B in 8085 Microprocessor

In this tutorial, we will learn how to access and exchange the content of flag register F with register B in 8085 Microprocessor? By Ayush Sharma Last updated : May 13, 2023

8085 program to access and exchange the content of Flag register with register B

Problem Statement

Write an assembly language program in 8085 microprocessor to access Flag register and exchange the content of flag register F with register B.

Assumptions

Initial values of flag register, register B and stack pointer are 00, 3F, and 3FFF respectively.

PSW stands for PROGRAM STATUS WORD. PSW combines accumulator A and flag register F.

Algorithm

1. Push the value of PSW in memory stack by help of PUSH instruction
2. Pop the value of Flag register and store it in register H by help of POP instruction
3. Move the value of register H in register C
4. Move the value of register B in register H
5. Move the value of register C in register B
6. Push the value of register H in memory stack by help of PUSH instruction
7. Pop the value of PSW from memory stack using POP instruction

Program

ADDRESS	MNEMONICS	COMMENTS
2000	PUSH PSW	Push value of accumulator and flag in stack
2001	POP H	Pop value from TOP of memory stack in H
2002	MOV C, H	C ← H
2003	MOV H, B	H ← B
2004	MOV B, C	B ← C
2005	PUSH H	Push the value of register H
2006	POP PSW	Pop value of flag register and Accumulator
2007	HLT	END

Explanation – Registers used A, B, C, H, F

1. PUSH PSW instruction performs the following task:
   • SP ← SP - 1
   • M[SP] ← A
   • SP ← SP - 1
   • M[SP] ← F
2. POP H instruction performs the following task:
   • H ← M[SP]
   • SP ← SP + 1
3. MOV C, H – moves the value of H in register C
4. MOV H, B – moves the value of B in register H, hence H is updated
5. MOV B, C – moves the value of C in register B, hence B is updated
6. PUSH H performs the following task:
   • SP ← SP - 1
   • M[SP] ← H
7. POP PSW performs the following task:
   • F ← M[SP]
   • SP ← SP + 1
   • A ← M[SP]
   • SP ← SP + 1
8. HLT – stops executing the program and halts any further execution

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