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Write a set of instructions to read and complement the contents of the flag register.

Written by @
Apparatus Used: Microprocessor Kit, Keyboard
Assumption: In 8085, the contents of flag register and the accumulator together are called program status word (PSW). The PSW can be accessed by only using PUSH and POP instructions. The PUSH instructions move the flag register contents (as lower byte order) and the accumulator contents (as higher byte order) of the stack.
 
Algorithm:
  • Push the contents of the accumulator and the flag register onto the stack.
  • Bring the PSW to HL pair
  • Move the contents of the flag register to the accumulator
  • Complement the accumulator
  • Store the complemented flags in register L
  • Push the contents of the HL register pair onto the stack
  • Pop it back to the PSW
  • End the Program
Program:
Memory Address
Op-code
Operand
Comments
2000
PUSH
PSW
Push the contents of A and Flag in Stack
2003
POP
H
Store PSW in H-L pair
2004
MOV
A,L
Move the contents of Flag Register in A
2007
CMA
A,E
Complement the Accumulator  
2009
MOV
L,A
Store complemented flag in register L
200A
PUSH
H
Push the contents of HL pair onto stack
2010
RST
5
Set Break Point(Optional)
2011
END
End the program
Used Instruction:
PUSH: This instruction pushes the contents of the register pair onto a stack.
POP: Pops the top two memory locations on the stack on a register pair.
MOV rd, rs: This instruction copies data from the source register into destination register.
CMA: Complements the contents of accumulator.
RST 5: This instruction is used to set break-point for the execution.
END: This instruction is used to execute the program.

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