in CO and Architecture
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2 votes
2 votes

in CO and Architecture
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2 Answers

3 votes
3 votes
Best answer

The DAD instruction (Double Add) allows 16-bit addition between the HL register pair and any one of the BC, DE, HL, or SP register pairs, putting the result in HL. It takes a single operand which may be B, D, H, or SP. The carry flag is set to indicate overflow is sum exceeds 16 bits. The contents of source register pair is not altered 

so DAD H  performs

HL=HL+HL

Hence ans is B 

DAD D performs 

HL=HL+DE

DAD B performs 

HL=HL+BC 

DAD SP

HL=HL+SP

edited by
1 vote
1 vote

HL is a pair of registers being used in 8085 microprocessor..So together H and L registers comprise of 16 bit operand..

Hence for addition of 16 bit numbers we require separate instruction so we have DAD instruction instead of ADD instruction..Further we are operating on HL pair registers..

Hence B) is the correct answer..