GATE | GATE-CS-2002 | Question 29

What are the states of the Auxiliary Carry (AC) and Carry Flag (dCY) after executing the following 8085 program?

   MVI L, 5DH
   MVI L, 6BH
   MOV A, H
   ADD L

(A) AC = 0 and CY = 0
(B) AC = 1 and CY = 1
(C) AC = 1 and CY = 0
(D) AC = 0 and CY = 0


Answer: (C)

Explanation: First we load  5D in L register But we have not stored it to the accumulator So, when we load 6B in L register, it overwrites 5D in L register and the same value 6BH is copied to accumulator

Now A = 6BH
L = 6BH
ADD L i.e. A = A + L
It will generate internal carry i.e. B + B = 22 i.e. 22 – 16 = 6
adding 2 to 6 + 6 => we get 14 => D
Hence answer is D6
Since there is internal carry only, no final carry as 14 < 16 So, Auxiliary carry flag(AC) = 1 Carry Flag(CY) = 0    

This solution is contributed by Mohit Gupta .

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