GATE | GATE-CS-2004 | Question 90

In an SR latch made by cross-coupling two NAND gates, if both S and R inputs are set to 0, then it will result in
(A) Q = 0, Q’ = 1
(B) Q = 1, Q’ = 0
(C) Q = 1, Q’ = 1
(D) Indeterminate states


Answer: (C)

Explanation: When both R and S are set as 0, we will get both Q and Q’ as 1. This output will be permanent and it is not dependent on any order of occurrence it only depends on the input values [NO RACE CONDITION].
But after this state if we make R=S=1, the output will be indeterminate depending on which NAND gate processes first (either Q or Q’ will become 0 but we can’t determine which [RACE CONDITION] and it will lead to an indeterminate state.

So, option (C) is correct.

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