Question

Explain the following instructions of 8085 Microprocessor with one
example of each : PUSH PSW

Answer 1

PUSH PSW : [PUSH ACCUMULATOR AND FLAG REGISTER ON STACK]
Format: [[SP] - 1] ←[A]
[[SP]- 2]₀ ←[Cy], [[SP]-2]₁ ←x,
[[SP]-2]₂ ←[P], [[SP]-2]₃ ←x,
[[SP]-2]₄ ←[Ac], [[SP]-2]₅ ←x,
[[SP]-2]₆ ←[Z], [[SP]-2]₇ ←S ,
[SP]←[SP]-2 (x -Undefined)
Addressing: Register indirect addressing
Bytes : 1 byte
Flag : None

Comment:
(1) The content of accumulator are moved to the memory location, whose address is one less than the content of stack pointer.
(2) The content of processor status word (flag register) are moved to the memory location, whose address is two less than the content of stack pointer.
(3) The stack pointer is decremented by 2

Example: Let [A] = 33 H and Flag Register = 25 H, [SP] = D015
Instruction: PUSH PSW
After execution : [D014] = 33 H, [D013] = 25H
[SP] = D013 H

Answer 2

PUSH PSW : [PUSH ACCUMULATOR AND FLAG REGISTER ON STACK]
Format: [[SP] - 1] ←[A]
[[SP]- 2]₀ ←[Cy], [[SP]-2]₁ ←x,
[[SP]-2]₂ ←[P], [[SP]-2]₃ ←x,
[[SP]-2]₄ ←[Ac], [[SP]-2]₅ ←x,
[[SP]-2]₆ ←[Z], [[SP]-2]₇ ←S ,
[SP]←[SP]-2 (x -Undefined)
Addressing: Register indirect addressing
Bytes : 1 byte
Flag : None

Comment:
(1) The content of accumulator are moved to the memory location, whose address is one less than the content of stack pointer.
(2) The content of processor status word (flag register) are moved to the memory location, whose address is two less than the content of stack pointer.
(3) The stack pointer is decremented by 2

Example: Let [A] = 33 H and Flag Register = 25 H, [SP] = D015
Instruction: PUSH PSW
After execution : [D014] = 33 H, [D013] = 25H
[SP] = D013 H