Carry and Auxiliary Carry Flags

Correct Answer

A — CY = 0, AC = 0

Concept and Reasoning

C2H + 3DH = FFH. There is no carry out of bit 7, so CY=0. In the lower nibble, 2H+DH=FH, which also produces no carry from bit 3 to bit 4, so AC=0. The flag pair therefore corresponds to option A.

Calculation / Key Relation

C2H+3DH=FFH

CY=0

AC=0

Exam Takeaway

CY checks carry out of bit 7; AC checks carry from bit 3 to bit 4.

Common Mistake

Do not set AC merely because the lower-nibble result is F; AC requires a carry beyond F.