In an SR latch made by cross-coupling two NAND gates, if both S and R inputs…
2007
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: D
In an SR latch made from cross-coupled NAND gates, the inputs are active-low.
When S = 0 and R = 1, the latch is set.
When S = 1 and R = 0, the latch is reset.
When S = 1 and R = 1, the latch holds the previous state.
The problematic case is S = R = 0. While these inputs are held low, both NAND outputs are forced to 1. This violates the required complementary relation between Q and Q'. When the inputs are returned to the inactive state, the final stored state depends on gate delays and can become unpredictable.
Therefore, this condition is treated as the forbidden/indeterminate state. The correct answer is Indeterminate states.
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