S–R NAND latch behavior If both inputs of an S–R NAND latch are driven LOW simultaneously, what happens at the outputs?

Introduction / Context:NAND-based S–R latches interpret LOW as the active assertion of Set or Reset. Applying LOW to both inputs simultaneously produces a forbidden condition. Understanding this case prevents design errors and metastability in larger systems where latches are sub-elements.

Given Data / Assumptions:

• NAND S–R latch (active-LOW S and R).
• Both inputs forced LOW at the same time.
• Standard cross-coupled configuration.

Concept / Approach:

For a NAND gate, any LOW input forces a HIGH output. With both inputs LOW, each NAND output goes HIGH, momentarily giving Q = 1 and Q̄ = 1, which violates complementarity. When inputs return HIGH, slight asymmetries decide the final latched state, making it unpredictable or indeterminate.

Step-by-Step Explanation:

Verification / Alternative check:

Timing diagrams show both outputs driven HIGH during the forbidden input, then a potentially random resolution after inputs are released, consistent with the latch truth table warning.

Why Other Options Are Wrong:

• Toggle (b) implies deterministic alternation, which does not occur.
• Reset (c) or no change (d) depend on valid inputs, not on the forbidden case.
• Complementary outputs (e) contradict the actual simultaneous HIGH outputs during the violation.

Common Pitfalls:

• Confusing NAND and NOR versions; the forbidden combination differs.
• Assuming hardware will always settle to a preferred state; it may vary each time.

Final Answer:

The output would become unpredictable (forbidden state).