8086-ASSEMBLY-LANGUAGE-PROGRAMS/Source Code/Stack Operations/push_pop.asm at main · Amey-Thakur/8086-ASSEMBLY-LANGUAGE-PROGRAMS · GitHub

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; =============================================================================
; TITLE: PUSH and POP Mechanics
; DESCRIPTION: Demonstrate the fundamental Last-In-First-Out (LIFO) behavior
;              of the 8086 hardware stack through register manipulation.
; AUTHOR: Amey Thakur (https://github.com/Amey-Thakur)
; REPOSITORY: https://github.com/Amey-Thakur/8086-ASSEMBLY-LANGUAGE-PROGRAMS
; LICENSE: MIT License
; =============================================================================

.MODEL SMALL
.STACK 100H

; -----------------------------------------------------------------------------
; DATA SEGMENT
; -----------------------------------------------------------------------------
.DATA
    MSG DB 'Stack Operations Trace - Observe Registers in Debugger$'

; -----------------------------------------------------------------------------
; CODE SEGMENT
; -----------------------------------------------------------------------------
.CODE
MAIN PROC
    ; Initialize context
    MOV AX, @DATA
    MOV DS, AX

    ; 1. PUSH OPERATIONS
    ; Values are added to the stack; SP (Stack Pointer) decrements by 2.
    MOV AX, 1234H
    PUSH AX                         ; Stack Top: 1234H

    MOV BX, 5678H
    PUSH BX                         ; Stack Top: 5678H, 1234H

    MOV CX, 9ABCH
    PUSH CX                         ; Stack Top: 9ABCH, 5678H, 1234H

    ; 2. POP OPERATIONS
    ; Values are removed in reverse order; SP increments by 2.
    POP DX                          ; DX = 9ABCH (Last pushed)
    POP DX                          ; DX = 5678H
    POP DX                          ; DX = 1234H (First pushed)

    ; Graceful Exit
    MOV AH, 4CH
    INT 21H
MAIN ENDP
END MAIN

; =============================================================================
; TECHNICAL NOTES
; =============================================================================
; 1. STACK MECHANICS:
;    - The stack grows "downwards" in memory (from higher towards lower addresses).
;    - PUSH: Decrements SP by 2, then copies word to [SS:SP].
;    - POP: Copies word from [SS:SP], then increments SP by 2.
;    - PUSH/POP must operate on 16-bit (Word) operands in 8086.
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