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.
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.
To draw the stack and its content for the duration of the program execution, we would need to trace the changes to the stack pointer (SP) and the values being pushed and popped from the stack.
Initially, the stack pointer (SP) is set to 0460H. Therefore, the stack is empty.
Step 1: MOV SP, 0460H
- The SP is updated to 0460H.
Stack (Addr):
0460H: Empty
Step 2: MOV AL, 1
- A value of 1 is moved to the AL register.
Stack (Addr):
0460H: Empty
Step 3: MOV BX, 0
- A value of 0 is moved to the BX register.
Stack (Addr):
0460H: Empty
Step 4: MOV CX, 7
- A value of 7 is moved to the CX register.
Stack (Addr):
0460H: Empty
Step 5: CALL SHERIDAN
- The address of the next instruction (0420H) is pushed onto the stack.
Stack (Addr):
0460H: 0420H
Step 6: SHL AL, 1
- The AL register value is shifted left by 1.
Stack (Addr):
0460H: 0420H
Step 7: OUT 0, AL
- The AL register value (after shifting) is sent to output port 0.
Stack (Addr):
0460H: 0420H
Step 8: LOOP AGAIN
- The CX register is decremented by 1.
Stack (Addr):
0460H: 0420H
Step 9: CALL SHERIDAN
- The address of the next instruction (0420H) is pushed onto the stack.
Stack (Addr):
0460H: 0420H: 0420H
Step 10: SHL AL, 1
- The AL register value is shifted left by 1.
Stack (Addr):
0460H: 0420H: 0420H
Step 11: OUT 0, AL
- The AL register value (after shifting) is sent to output port 0.
Stack (Addr):
0460H: 0420H: 0420H
Step 12: LOOP AGAIN
- The CX register is decremented by 1.
Stack (Addr):
0460H: 0420H: 0420H
Step 13: CALL SHERIDAN
- The address of the next instruction (0420H) is pushed onto the stack.
Stack (Addr):
0460H: 0420H: 0420H: 0420H
Step 14: SHL AL, 1
- The AL register value is shifted left by 1.
Stack (Addr):
0460H: 0420H: 0420H: 0420H
Step 15: OUT 0, AL
- The AL register value (after shifting) is sent to output port 0.
Stack (Addr):
0460H: 0420H: 0420H: 0420H
Step 16: LOOP AGAIN
- The CX register is decremented by 1.
Stack (Addr):
0460H: 0420H: 0420H: 0420H
Step 17: CALL SHERIDAN
- The address of the next instruction (0420H) is pushed onto the stack.
Stack (Addr):
0460H: 0420H: 0420H: 0420H: 0420H
Step 18: SHL AL, 1
- The AL register value is shifted left by 1.
Stack (Addr):
0460H: 0420H: 0420H: 0420H: 0420H
Step 19: OUT 0, AL
- The AL register value (after shifting) is sent to output port 0.
Stack (Addr):
0460H: 0420H: 0420H: 0420H: 0420H
Step 20: LOOP AGAIN
- The CX register is decremented by 1.
Stack (Addr):
0460H: 0420H: 0420H: 0420H: 0420H
Step 21: INT3
- Interrupt instruction, no change to the stack.
Stack (Addr):
0460H: 0420H: 0420H: 0420H: 0420H
At this point, the program ends and the stack remains unchanged.
Please note that the content of the stack is represented in hexadecimal format.
To draw the stack and its content during the execution of the given program, we can analyze the program step by step and keep track of the changes to the stack.
1. The program starts at address 0x0400. We initialize the stack pointer (SP) to 0x0460:
Stack: [Empty]
2. MOV AL, 1
The value in accumulator AL is set to 1. This does not affect the stack.
3. MOV BX, 0
The value in register BX is set to 0. This does not affect the stack.
4. MOV CX, 7
The value in register CX is set to 7. This does not affect the stack.
5. CALL SHERIDAN
The address of the next instruction (0420H) is pushed onto the stack. Stack pointer (SP) is decremented by 2.
Stack: [0420H] (SP: 045E)
6. SHERIDAN:
PUSH CX
The value in register CX (7) is pushed onto the stack. Stack pointer (SP) is decremented by 2.
Stack: [0420H, 0007H] (SP: 045C)
7. MOV CX, AABBH
The value in register CX is set to AABBH (a hexadecimal value). This does not affect the stack.
8. LOOP $
Since CX (AABBH) is nonzero, the loop is executed. The address of the next instruction (0420H) is pushed onto the stack. Stack pointer (SP) is decremented by 2.
Stack: [0420H, 0007H, 0420H] (SP: 045A)
9. POP CX
The value at the top of the stack (0420H) is popped into register CX. Stack pointer (SP) is incremented by 2.
Stack: [0420H, 0007H] (SP: 045C)
10. RET
The address from the top of the stack (0420H) is popped and execution resumes from that address. Stack pointer (SP) is incremented by 2.
Stack: [0007H] (SP: 045E)
11. SHL AL, 1
The value in accumulator AL is shifted left by 1 bit. This does not affect the stack.
12. OUT 0, AL
The value in AL is outputted to port 0. This does not affect the stack.
13. LOOP AGAIN
Since the current value in CX (0007H) is nonzero, the loop is executed. The address of the next instruction (0420H) is pushed onto the stack. Stack pointer (SP) is decremented by 2.
Stack: [0420H, 0007H, 0420H] (SP: 045C)
14. INT3
The interrupt instruction INT3 is executed. This does not affect the stack.
At the end of the program execution, the stack will contain the following values:
Stack: [0420H, 0007H, 0420H] (SP: 045C)
Note: The drawing of the stack may vary depending on the specific representation format used, but the content and changes to the stack should be accurately reflected.