Engineering Questions with Answers - Multiple Choice Questions

# MCQs on Instruction Set of 8086/8088 – 2

1 - Question

The instruction, “INC” increases the contents of the specified register or memory location by
a) 2
b) 0
c) 1
d) 3

Explanation: This instruction adds 1 to the contents of the operand and so increments by 1.

2 - Question

The instruction that subtracts 1 from the contents of the specified register/memory location is
a) INC
b) SUBB
c) SUB
d) DEC

Explanation: The DEC instruction decrements the contents of a specified register/memory location by 1.

3 - Question

The instruction that enables subtraction with borrow is
a) DEC
b) SUB
c) SBB
d) None of the mentioned

Explanation: The SBB instruction subtracts the source operand and the borrow flag from the destination operand.

4 - Question

The flag that acts as Borrow flag in the instruction, SBB is
a) direction flag
b) carry flag
c) parity flag
d) trap flag

Explanation: If borrow exists in the subtraction operation performed then carry flag is set.

5 - Question

In general, the source operand of an instruction can be
a) memory location
b) register
c) immediate data
d) all of the mentioned

Explanation: The source operand is the element which is data or data stored memory location on which operation is performed.

6 - Question

In general, the destination operand of an instruction can be
a) memory location
b) register
c) immediate data
d) memory location and register

Explanation: Since the destination should be able to store the data, immediate data cannot be considered as a destination operand.

7 - Question

The instruction, CMP to compare source and destination operands it performs
b) subtraction
c) division
d) multiplication

Explanation: For comparison, the instruction CMP subtracts source operand from destination operand.

8 - Question

During comparison operation, the result of comparing or subtraction is stored in
a) memory
b) registers
c) stack
d) no where

Explanation: The result of subtraction operation is not stored anywhere during a comparison.

9 - Question

The instruction that converts the result in an unpacked decimal digits is
a) AAA
b) AAS
c) AAM
d) All of the mentioned

Explanation: All the ASCII adjust instructions give result in unpacked decimal form and so are called as “Unpacked BCD arithmetic instructions”.

10 - Question

Which of the following is a mnemonic?
c) AAA

Explanation: AAA is a mnemonic. It doesn’t have either a source or destination operand.

11 - Question

The instruction in which adjustment is made before performing the operation is
a) AAA
b) AAS
c) AAM

Explanation: 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 - Question

The expansion of DAA is

Explanation: This instruction performs conversion operation.

13 - Question

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

Explanation: In this conversion, the result has to be only in AL.

14 - Question

The ROR instruction rotates the contents of the destination operand to
a) left
b) right
c) left and then right
d) right and then left