ISRO2008-39

Question

Consider the following Assembly language program

MVIA	30 H
ACI	30 H
XRA	A
POP	H

After the execution of the above program, the contents of the accumulator will be

• A. $\textsf{30 H}$
• B. $\textsf{60 H}$
• C. $\textsf{00 H}$
• D. contents of stack

Comments

First instruction should be MVI A,30H

Answer 1

MVI: - move immediate data to a register or memory location.

ACI: - Add immediate to accumulator with carry.

XRA: - The content of accumulator are exclusive OR with specified register or memory location.

So after first instruction execution, Accumulator(assuming 8 bit) value will be A=30H=0011 0000

After second Instruction A=30+30=60H=0110 0000

After third Instruction A=A⊕A=0010 0000⊕0010 0000=0000 0000=00H

correct answer is C

Comments

What does POP H mean

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What is significant of fourth statement

POP H ?

at last if I POP contents of Accumulator to H, then what will be the value left in the Accumulator?

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In 8085 microprocessor, POP H is interpreted as:

Content at the memory location pointed stack pointer is copied into register pair specified in instruction operand field (HL pair in this case).

Thus, execution of the last instruction has no effect on the contents of Accumulator. Thereby, the answer remains the same.

(Reference)

Answer 2

XRA A means exclusive OR of Acumulator content with itself. Whatever the value would be of acumulator, ans is zero. Beacuse same number XOR operation with itself is zero.