In an SR latch made by cross-coupling two NAND gates, if both S and R inputs…
2004
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
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Correct answer: C
Answer: Q = 1, Q' = 1.
Explanation: In a cross-coupled NAND SR latch each NAND output goes to 1 if any of its inputs is 0. If both S and R are set to 0, each NAND gate receives a 0 input and therefore drives its output to 1, producing Q = 1 and Q' = 1.
How it happens: S = 0 forces the gate that drives Q to 1, and R = 0 forces the gate that drives Q' to 1, so both outputs become 1 due to the NAND truth behavior.
Why this is avoided: When S and R return to 1, the latch may become indeterminate because both outputs were 1 and tiny differences in gate propagation determine which output changes first. Therefore the both-0 input condition is considered a forbidden or undesirable input in normal operation.
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