Microprocessors Questions and Answers – Enhanced Instruction Set of 80386

This set of Microprocessor Multiple Choice Questions & Answers (MCQs) focuses on “Enhanced Instruction Set of 80386”.

1. Which of the following is not a newly added instruction of 80386, that are not present in 80286?
a) bit scan instructions
b) bit test instructions
c) shift double instructions
d) none of the mentioned
View Answer

Answer: d
Explanation: The newly added instructions of 80386 are categorized into
1. bit scan instructions
2. bit test instructions
3. conditional set byte instructions
4. shift double instructions
5. control transfer via gates instructions.

2. The BSF (bit scan forward) instruction scans the operand in the order
a) from left to right
b) from right to left
c) from upper nibble
d) none of the mentioned
View Answer

Answer: b
Explanation: The BSF (bit scan forward) instruction scans the operand from right to left.

3. The BSR (bit scan reverse) instruction scans the operand in the order
a) from left to right
b) from right to left
c) from upper nibble
d) none of the mentioned
View Answer

Answer: a
Explanation: The BSR (bit scan reverse) instruction scans the operand from left to right.
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4. If a ‘1’ is encountered when an operand is scanned by BSF, then
a) zero flag is reset
b) zero flag is set
c) VM flag is set
d) RF flag is reset
View Answer

Answer: b
Explanation: The BSF instruction scans the operand from right to left. If a ‘1’ is encountered during the scan, zero flag is set, and the bit position of ‘1’ is stored into the destination operand.

5. If a ‘1’ is not encountered when an operand is scanned by BSR, then
a) zero flag is reset
b) zero flag is set
c) VM flag is reset
d) RF flag is set
View Answer

Answer: a
Explanation: The BSR instruction scans the operand from left to right. If a ‘1’ is not encountered during the scan, zero flag is reset whether the scan is BSF or BSR.
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6. Which of the following is not a bit test instruction?
a) BTC
b) BTS
c) BSF
d) BTR
View Answer

Answer: c
Explanation: The instruction, BSF, is a bit scan instruction. The four bit test instructions are:
BT (Test a Bit), BTC (Test a Bit and Complement), BTR (Test and Reset a Bit) and BTS (Test and Set a bit).

7. In case of BT instruction, if the bit position in the destination operand specified by the source operand, is ‘1’, then
a) zero flag is reset
b) carry flag is set
c) VM flag is set
d) RF flag is reset
View Answer

Answer: b
Explanation: In case of BT instruction, if the bit position in the destination operand specified by the source operand, is ‘1’, the carry flag is set, otherwise it is cleared.
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8. Which of the following is not a conditional set byte instruction?
a) SETNP
b) SETO
c) SETNAE
d) SHRD
View Answer

Answer: d
Explanation: The SHRD (Shift Right Double) is a shift double instruction.

9. The instruction that shifts the specified number of bits in the instruction, from the upper side of the source operand into the lower side of the destination operand is
a) SHRD
b) SHLD
c) SETNS
d) None of the mentioned
View Answer

Answer: b
Explanation: The SHLD instruction shifts the specified number of bits in the instruction, from the upper side (i.e. MSB) of the source operand into the lower side (i.e. LSB) of the destination operand.
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10. The instruction that shifts 8 LSB bits of ECX into the MSB positions of EAX, one by one starting from LSB of ECX is
a) SHLD ECX,EAX,8
b) SHLD EAX,ECX,8
c) SHRD ECX,EAX,8
d) SHRD EAX,ECX,8
View Answer

Answer: d
Explanation: The SHRD instruction shifts the specified number of bits in the instruction, from the lower side (i.e. LSB) of the source operand into the upper side (i.e. MSB) of the destination operand.

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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