250+ TOP MCQs on Instruction Set of 8086/8088 – 2 and Answers

Microprocessors Interview Questions and Answers on “Instruction Set of 8086/8088 – 2”.

1. The instruction, “INC” increases the contents of the specified register or memory location by
a) 2
b) 0
c) 1
d) 3
Answer: c
Clarification: This instruction adds 1 to the contents of the operand and so increments by 1.

2. The instruction that subtracts 1 from the contents of the specified register/memory location is
a) INC
b) SUBB
c) SUB
d) DEC
Answer: d
Clarification: The DEC instruction decrements the contents of a specified register/memory location by 1.

3. The instruction that enables subtraction with borrow is
a) DEC
b) SUB
c) SBB
d) None of the mentioned
Answer: c
Clarification: The SBB instruction subtracts the source operand and the borrow flag from the destination operand.

4. The flag that acts as Borrow flag in the instruction, SBB is
a) direction flag
b) carry flag
c) parity flag
d) trap flag
Answer: b
Clarification: If borrow exists in the subtraction operation performed then carry flag is set.

5. In general, the source operand of an instruction can be
a) memory location
b) register
c) immediate data
d) all of the mentioned
Answer: d
Clarification: The source operand is the element which is data or data stored memory location on which operation is performed.

6. In general, the destination operand of an instruction can be
a) memory location
b) register
c) immediate data
d) memory location and register
Answer: d
Clarification: Since the destination should be able to store the data, immediate data cannot be considered as a destination operand.

7. The instruction, CMP to compare source and destination operands it performs
a) addition
b) subtraction
c) division
d) multiplication
Answer: b
Clarification: For comparison, the instruction CMP subtracts source operand from destination operand.

8. During comparison operation, the result of comparing or subtraction is stored in
a) memory
b) registers
c) stack
d) no where
Answer: d
Clarification: The result of subtraction operation is not stored anywhere during a comparison.

9. The instruction that converts the result in an unpacked decimal digits is
a) AAA
b) AAS
c) AAM
d) All of the mentioned
Answer: d
Clarification: All the ASCII adjust instructions give result in unpacked decimal form and so are called as “Unpacked BCD arithmetic instructions”.

10. Which of the following is a mnemonic?
a) ADD
b) ADC
c) AAA
d) ADD & ADC
Answer: c
Clarification: AAA is a mnemonic. It doesn’t have either a source or destination operand.

11. The instruction in which adjustment is made before performing the operation is
a) AAA
b) AAS
c) AAM
d) AAD
Answer: d
Clarification: The AAD instruction converts two unpacked BCD digits in AH and AL to the equivalent binary number in AL. This adjustment must be made before dividing the two unpacked BCD digits.

12. The expansion of DAA is
a) decimal adjust after addition
b) decimal adjust before addition
c) decimal adjust accumulator
d) decimal adjust auxiliary
Answer: c
Clarification: This instruction performs conversion operation.

13. The instruction that is used to convert the result of the addition of two packed BCD numbers to a valid BCD number is
a) DAA
b) DAS
c) AAA
d) AAS