Engineering Questions with Answers - Multiple Choice Questions

# MCQs on 8051 Instruction Set -2

1 - Question

If the most significant bit of relative address byte is 1, then the short jump instruction is
a) forward jump
b) back jump
c) either forward or back jump
d) none

Explanation: If the most significant bit of relative address byte is 1, then the short jump instruction is back jump, else it is considered as forward jump.

2 - Question

The first byte of an absolute jump instruction consists of
a) 3 LSBs of opcode and 5 MSBs of 11-bit address
b) 5 MSBs of opcode and 3 LSBs of 11-bit address
c) 6 MSBs of opcode and 1 LSB of 11-bit address
d) 5 LSBs of opcode and 3 MSBs of 11-bit address

Explanation: The first byte of an absolute jump instruction consists of 5 LSBs of opcode and 3 MSBs of 11-bit address. The next byte carries the least significant 8 bits of the 11-bit address.

3 - Question

The third byte of the long jump instruction is
a) opcode
b) 5 LSBs of opcode
c) higher byte of jump location or subroutine
d) lower byte of jump location or subroutine

Explanation: The third byte of the long jump instruction is a higher byte of jump location or subroutine.

4 - Question

The absolute jump instruction is intended mainly for a jump within a memory space of
a) 2 bytes
b) 2 Kbytes
c) 2 Mbytes
d) none

Explanation: The absolute jump instruction is intended mainly for a jump within a memory space of 2 Kbytes.

5 - Question

The LJMP instruction is very useful in programming in the external code memory space of
a) 32 MB
b) 64 MB
c) 32 KB
d) 64 KB

Explanation: The LJMP instruction is very useful in programming in the external code memory space of 64 KB.

6 - Question

Which of the following is not an unconditional control transfer instruction?
a) JMP
b) RET
c) JNC
d) CALL

Explanation: The instructions, JMP, RET, RETI, CALL are the unconditional control transfer instructions.

7 - Question

The conditional control transfer instructions use
a) status flags
b) bits of bit addressable RAM
c) SFRs termed bit
d) all of the mentioned

Explanation: The conditional control transfer instructions use status flags or bits of bit addressable RAM or SFRs termed bit.

8 - Question

Which of the following is not a conditional control transfer instruction?
a) JC
b) JBC
c) JNC
d) NONE

Explanation: The instructions, JC, JBC, JNC, JB and JNB are the conditional control transfer instructions.

9 - Question

The mnemonic used to perform a subtraction of source with an 8-bit data and jumps to specified relative address if subtraction is non-zero is
a) DJNZ
b) CJNE
c) JZ
d) JNC

Explanation: The CJNE instruction perform a subtraction of source with an 8-bit data and jumps to specified relative address only if the result of the subtraction is non-zero, else continues to the next instruction.

10 - Question

a) specified bit=1
b) specified bit=0
c) specified bit is non-recursive
d) none

Explanation: The mnemonic, JNB is used to jump to the specified relative address only if specified bit=1, else continues to the next instruction.

11 - Question

The type of operand that is not allowed to use in boolean instructions of 8051 is
a) direct register operands
b) indirect register operands
c) immediate bit
d) none

Explanation: In boolean instructions, the immediate bit is not allowed as an operand.

12 - Question

In boolean instructions, the flag that is the only allowed destination operand for two operand instructions is
a) overflow flag
b) underflow flag
c) auxiliary flag
d) carry flag