GATE 2022 BM – Question 17
Input bits X and Y are added by the combinational logic shown. S is their sum bit. For correct operation, what are D₀,D₁,D₂,D₃ in that order?
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Correct answer: (A) 1,0,0,1
Explanation
The sum bit is X XOR Y, so it is one for unequal inputs and zero for equal inputs. Trace the actual AND-gate select wiring: D₀ and D₃ select the unequal-input combinations, while D₁ and D₂ select the equal-input combinations. Thus D₀=D₃=1 and D₁=D₂=0, giving A. The gate labels are not in standard binary minterm order.