Engineering Questions with Answers - Multiple Choice Questions

MCQs on Instruction Set of 8086/8088 – 3

1 - Question

The mnemonic that is placed before the arithmetic operation is performed is
a) AAA
b) AAS
c) AAM
d) AAD

View Answer

Answer: d
Explanation: The AAD instruction converts two unpacked BCD digits in AH and AL to the equivalent binary number in AL.




2 - Question

The Carry flag is undefined after performing the operation
a) AAA
b) ADC
c) AAM
d) AAD

View Answer

Answer: d
Explanation: Since the operation, AAD is performed before division operation is performed, the carry flag, auxiliary flag and overflow flag are undefined.




3 - Question

The instruction that performs logical AND operation and the result of the operation is not available is
a) AAA
b) AND
c) TEST
d) XOR

View Answer

Answer: c
Explanation: In the TEST instruction, the logical AND operation is performed and the result is not stored but flags are affected.




4 - Question

In the RCL instruction, the contents of the destination operand undergo function as
a) carry flag is pushed into LSB & MSB is pushed into the carry flag
b) carry flag is pushed into MSB & LSB is pushed into the carry flag
c) auxiliary flag is pushed into LSB & MSB is pushed into the carry flag
d) parity flag is pushed into MSB & LSB is pushed into the carry flag

View Answer

Answer: a
Explanation: In RCL(Rotate right through carry), for each operation, the carry flag is pushed into LSB and the MSB of the operand is pushed into carry flag.




5 - Question

The instruction that is used as prefix to an instruction to execute it repeatedly until the CX register becomes zero is
a) SCAS
b) REP
c) CMPS
d) STOS

View Answer

Answer: b
Explanation: The instruction to which the REP is prefix, is executed repeatedly until CX register becomes zero. When CX becomes zero, the execution proceeds to the next instruction in sequence.




6 - Question

Match the following

A) MOvSB/SW       1) loads AL/AX register by content of a string
B) CMPS           2) moves a string of bytes stored in source to destination
C) SCAS           3) compares two strings of bytes or words whose length is stored in CX register
D) LODS           4) scans a string of bytes or words

a) A-3,B-4,C-2,D-1
b) A-2,B-1,C-4,D-3
c) A-2,B-3,C-1,D-4
d) A-2,B-3,C-4,D-1

View Answer

Answer: d
Explanation: By using the string instructions, the operations on strings can be performed.




7 - Question

The instructions that are used to call a subroutine from the main program and return to the main program after execution of called function are
a) CALL, JMP
b) JMP, IRET
c) CALL, RET
d) JMP, RET

View Answer

Answer: c
Explanation: At each CALL instruction, the IP and CS of the next instruction are pushed onto the stack, before the control is transferred to the procedure. At the end of the procedure, the RET instruction must be executed to retrieve the stored contents of IP & CS registers from a stack.




8 - Question

The instruction that unconditionally transfers the control of execution to the specified address is
a) CALL
b) JMP
c) RET
d) IRET

View Answer

Answer: b
Explanation: In this the control transfers to the address specified in the instruction and flags are not affected by this instruction.




9 - Question

Which instruction cannot force the 8086 processor out of ‘halt’ state?
a) Interrupt request
b) Reset
c) Both interrupt request and reset
d) Hold

View Answer
Answer: d
Explanation: Only an interrupt request or Reset will force the 8086 processor to come out of the ‘halt’ state.

 




10 - Question

NOP instruction introduces
a) Address
b) Delay
c) Memory location
d) None of the mentioned

View Answer

Answer: b
Explanation: NOP is the No operation. It means that the processor performs no operation for the clock cycle and thus there exists a delay.




11 - Question

Which of the following is not a machine controlled instruction?
a) HLT
b) CLC
c) LOCK
d) ESC

View Answer

Answer: b
Explanation: Since CLC is a flag manipulation instruction where CLC stands for Clear Carry Flag.

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