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Q1. Consider the following program segment given below: [5 POINTS]

ORG 0x0400
Address
0400h MOV SP, 0460H
MOV AL, 1
MOV BX, 0
MOV CX, 7
AGAIN: CALL SHERIDAN
0420H SHL AL, 1
OUT 0, AL
LOOP AGAIN
INT3
SHERIDAN:
PUSH CX
MOV CX, AABBH
LOOP $
POP CX
RET
In executing the above program, the Microprocessor is using the stack. In that respect, draw the stack along with its content for the duration of the program execution.

5 answers

Based on the given program segment, the stack is being utilized in the sub-routine SHERIDAN. Let's analyze the stack content for the duration of the program execution:

1. Initial stack state:
- Empty stack as the program hasn't started execution yet.

2. After the execution of the instructions from address 0400h to 0407h:
- Stack pointer (SP) is moved to 0460h after the execution of "MOV SP, 0460H".
- Stack content: (empty)

3. Execution enters the loop labeled "AGAIN":
- The program jumps to the SHERIDAN sub-routine at address 0420h.
- The current value of CX (7) is pushed onto the stack.
- Stack content: CX = 7

4. Execution enters the SHERIDAN sub-routine at address 0420h:
- The current value of CX (7) is moved to the register CX.
- The loop ("LOOP $") is executed with the value of CX being AABBH.
- This loop decrements CX until it becomes zero.
- During each iteration, CX is pushed onto the stack.
- After the completion of the loop, the initial value of 7 is popped from the stack to CX.
- Stack content: (empty) (CX values popped during the loop: AABBH, AAH, 99H, ...)
- The specific values depend on the number of iterations in the loop, but they form a descending pattern.

5. Execution returns to the main program after the completion of the SHERIDAN sub-routine:
- The loop "LOOP AGAIN" continues the execution until CX becomes zero.
- For each iteration, the AL register is shifted left by 1 (SHL AL, 1).
- The current value of AL is output to port 0 (OUT 0, AL).
- The stack remains unaffected during these instructions.
- Stack content: (empty)

6. After the completion of the loop "LOOP AGAIN":
- The program interrupts with an INT3 instruction.
- Stack content: (empty)

Note: The stack is mainly utilized in the SHERIDAN sub-routine, where it stores and retrieves the value of CX to be used in the loop.
Can make your explanation simpler
Certainly! Here's a simpler explanation of the stack content during program execution:

1. The program starts with an empty stack.

2. The stack pointer (SP) is moved to memory address 0460h.

3. The program enters a loop called "AGAIN" and jumps to a sub-routine called SHERIDAN.

4. Inside the SHERIDAN sub-routine:
- The current value of CX is pushed onto the stack.
- The value of CX is set to AABBH and a loop is executed.
- During each iteration of the loop, CX is pushed onto the stack.
- After the loop, the original value of CX is popped from the stack.

5. The program returns to the main program and continues the loop "LOOP AGAIN":
- The AL register is shifted left by 1 and the value is output to port 0.
- This loop continues until CX becomes zero.
- The stack remains empty during this loop.

6. The program ends with an interrupt instruction (INT3).

In summary, the stack is mainly used in the SHERIDAN sub-routine to store and retrieve the value of CX. During the main program execution, the stack remains empty.
Can you draw the stack along with its content for the duration of the program execution.
Certainly! Here is a visual representation of the stack along with its contents for the duration of the program execution:

```
Address | Content
---------------------
0460h |
-----------|----------
045Fh |
-----------|----------
045Eh |
-----------|----------
045Dh |
-----------|----------
045Ch |
-----------|----------
045Bh |
-----------|----------
045Ah |
-----------|----------
0459h |
-----------|----------
0458h |
-----------|----------
0457h |
-----------|----------
0456h |
-----------|----------
0455h |
-----------|----------
0454h |
-----------|----------
0453h |
-----------|----------
0452h |
-----------|----------
0451h |
-----------|----------
0450h |
-----------|----------
044Fh |
-----------|----------
044Eh |
-----------|----------
044Dh |
-----------|----------
044Ch |
-----------|----------
044Bh |
-----------|----------
044Ah |
-----------|----------
0449h |
-----------|----------
0448h |
-----------|----------
0447h |
-----------|----------
0446h |
-----------|----------
0445h |
-----------|----------
0444h |
-----------|----------
0443h |
-----------|----------
0442h |
-----------|----------
0441h |
-----------|----------
0440h |
-----------|----------
043Fh |
-----------|----------
043Eh |
-----------|----------
043Dh |
-----------|----------
043Ch |
-----------|----------
043Bh |
-----------|----------
043Ah |
-----------|----------
0439h |
-----------|----------
0438h |
-----------|----------
0437h |
-----------|----------
0436h |
-----------|----------
0435h |
-----------|----------
0434h |
-----------|----------
0433h |
-----------|----------
0432h |
-----------|----------
0431h |
-----------|----------
0430h |
-----------|----------
042Fh |
-----------|----------
042Eh |
-----------|----------
042Dh |
-----------|----------
042Ch |
-----------|----------
042Bh |
-----------|----------
042Ah |
-----------|----------
0429h |
-----------|----------
0428h |
-----------|----------
0427h |
-----------|----------
0426h |
-----------|----------
0425h |
-----------|----------
0424h |
-----------|----------
0423h |
-----------|----------
0422h |
-----------|----------
0421h |
-----------|----------
0420h |
-----------|----------
041Fh |
-----------|----------
041Eh |
-----------|----------
041Dh |
-----------|----------
041Ch |
-----------|----------
041Bh |
-----------|----------
041Ah |
-----------|----------
0419h |
-----------|----------
0418h |
-----------|----------
0417h |
-----------|----------
0416h |
-----------|----------
0415h |
-----------|----------
0414h |
-----------|----------
0413h |
-----------|----------
0412h |
-----------|----------
0411h |
-----------|----------
0410h |
-----------|----------
040Fh |
-----------|----------
040Eh |
-----------|----------
040Dh |
-----------|----------
040Ch |
-----------|----------
040Bh |
-----------|----------
040Ah |
-----------|----------
0409h |
-----------|----------
0408h |
-----------|----------
0407h | 1
-----------|----------
0406h |
-----------|----------
0405h |
-----------|----------
0404h |
-----------|----------
0403h |
-----------|----------
0402h |
-----------|----------
0401h |
-----------|----------
0400h |
-----------|----------
```

Please note that the stack grows downward in memory, meaning that the higher addresses are at the top of the diagram, while the lower addresses are at the bottom. The addresses and content in the diagram are examples and may vary based on the actual program execution.