Gated S-R latch (gated S-R “flip-flop”) hold behavior: Under which condition does a gated S-R storage element remain in the hold (no-change) state while it is enabled?

Difficulty: Easy

the Gate Enable is HIGH
the Gate Enable is LOW
the S and R inputs are both LOW
the Gate Enable is HIGH and the S and R inputs are both LOW

Correct Answer: the Gate Enable is HIGH and the S and R inputs are both LOW

Explanation:

Introduction / Context:
A gated S-R latch adds an enable (gate) control to the basic S-R latch so that input commands are effective only when the gate is asserted. Knowing the exact condition that causes a hold (no change) while enabled helps avoid accidental state changes and race-through issues in combinational-to-sequential interfaces.

Given Data / Assumptions:

Device: gated S-R latch with inputs S, R, and a Gate Enable (often E or G).
Active gate level is assumed HIGH (common textbook convention).
We are asking for the condition that yields “no change” while enabled.

Concept / Approach:
The gated S-R truth table typically includes: E=1, S=0, R=0 → no change; E=1, S=1, R=0 → set; E=1, S=0, R=1 → reset; E=1, S=1, R=1 → invalid; and for E=0 the latch ignores S and R and simply holds. The question explicitly focuses on the hold condition when the device is enabled, so we select E=1 with S=0 and R=0.

Step-by-Step Solution:

Confirm active enable level: Gate Enable HIGH means inputs are “looked at.”Identify hold row in the truth table: S=0 and R=0 gives “no change.”Combine: E=1 and S=R=0 implies enabled but holding.Hence, the correct condition is “Gate Enable HIGH and S and R both LOW.”

Verification / Alternative check:

Cross-check with a standard truth table from textbooks or datasheets; the mapping is consistent.

Why Other Options Are Wrong:

the Gate Enable is HIGH: Incomplete—S and R values must be specified.the Gate Enable is LOW: This also produces hold, but the question asks for the enabled case.the S and R inputs are both LOW: Incomplete without the enable context.

Common Pitfalls:

Forgetting that “enabled” narrows the condition subset.Confusing the enabled hold with the disabled ignore case.

Final Answer:

the Gate Enable is HIGH and the S and R inputs are both LOW

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Gated S-R latch (gated S-R “flip-flop”) hold behavior: Under which condition does a gated S-R storage element remain in the hold (no-change) state while it is enabled?

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