CS401 - Computer Architecture and Assembly Language Programming: Addressing Modes MCQs with Answers & Solutions | VU SIGMA – Page 11 of 40

Question 1

Compare the roles of the Code Segment Register (CS) and Data Segment Registers (DS / general data registers) in 8088 architecture.

Accepted Answer

1. Code Segment Register (CS):
- Purpose: Stores the base address of the 64 KB memory segment containing executable machine instructions [14, 18].
- Association: Tied strictly with the Instruction Pointer (IP) to form the logical instruction address CS:IP [18, 19].
- Overriding Restrictions: CS cannot be overridden for instruction execution; the CPU always fetches instructions from CS:IP [18, 19].

2. Data Segment Register (DS) and General Data Registers:
- Purpose: DS holds the base address of the 64 KB memory segment dedicated to program variables and data arrays [14, 30]. General data registers (AX, BX, CX, DX) hold immediate operands and intermediate arithmetic results [15, 16, 35].
- Association: DS is the default segment for memory references involving SI, DI, or BX [19].
- Overriding Capability: Data segment associations can be overridden using segment override prefixes (e.g., ES:, CS:, SS:) [19, 36].

Question 2

Which 8088 assembly instruction decrements the Stack Pointer (SP) by two bytes and then transfers a 16-bit word from the source operand onto the top of the stack?

Accepted Answer

PUSH

Answer

POP

Answer

CALL

Answer

MOV

Question 3

Provide valid 8088 assembly instruction(s) to copy the contents of the FLAGS register into register AX.

Accepted Answer

Because FLAGS cannot be referenced directly in MOV instructions, PUSHF and POP AX are used in sequence.

Assembly Code:
```assembly
pushf           ; Push FLAGS register image onto stack
pop ax          ; Pop top word from stack into AX register
```

Question 4

Describe the working mechanism and stack operation of the POP instruction in 8088 assembly language.

Accepted Answer

The POP instruction operates as follows:
1. Reads the 16-bit word located at memory address SS:SP and transfers it into the specified destination register or memory location.
2. Increments the Stack Pointer (SP) by 2 bytes (SP = SP + 2) to adjust the stack top.

Question 5

When the instruction 'push ax' is executed in a downward-growing (decrementing) stack, how does the value of SP (Stack Pointer) change?

Accepted Answer

Executing 'push ax' alters SP as follows:
1. The processor first decrements the Stack Pointer (SP) by 2 (SP = SP - 2).
2. The 16-bit value in AX is then stored at the physical memory address SS:SP.

Question 6

In 8088 assembly language instructions, a constant (immediate value) can never be used as a ________ operand.

Accepted Answer

Destination

Answer

Source

Answer

Memory

Answer

Register

Question 7

True or False: In 8088 assembly language, a single MOV instruction can copy data directly from one memory location to another memory location (e.g., 'mov [num2], [num1]').

Accepted Answer

False

Answer

True

Question 8

True or False: In 8088 assembly language, arithmetic and data movement instructions allow mixing operands of different sizes (such as adding an 8-bit register directly to a 16-bit register: 'add bx, al') without explicit zero/sign extension.

Accepted Answer

False

Answer

True

Question 9

In the 8088 assembly language instruction 'MOV AX, 5', how many operands are present?

Accepted Answer

2

Answer

1

Answer

3

Answer

4

Question 10

All memory addressing modes in the Intel 8088 (iAPX88) processor calculate an offset within a segment, which is called the ________ address.

Accepted Answer

Effective Address

Answer

Indirect Address

Answer

Direct Address

Answer

Faulty Address

Addressing Modes

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