Gated S–R flip-flop — condition for output change For a gated S–R flip-flop (latch with an enable/control input), the Q output changes state only if which condition about the control input and data is true?

Introduction / Context:
A gated S–R flip-flop includes an enable or control input that determines when the S and R inputs are allowed to affect the stored state. Understanding this gating is essential for preventing unintended state changes and for correct interfacing with asynchronous sources, such as mechanical switches or combinational logic that may glitch.

Given Data / Assumptions:

• The device has S and R inputs plus a control (enable) input.
• When the control input is inactive, the latch is opaque and holds state.
• When the control input is active, the latch is transparent to S/R commands.

Concept / Approach:
The output changes only when the control input allows the internal gating to pass the effects of S and/or R to the storage nodes. In many texts, this is phrased as “the output changes only when the control input changes from inactive to active (or is asserted).” In other words, a meaningful change on the control/enable that admits S/R information is required; otherwise, the latch holds its current state regardless of S and R line chatter.

Step-by-Step Solution:

Verification / Alternative check:
Examine a gated S–R symbol and truth table: the enable (or C) input qualifies S and R; without enable, the next-state function equals present state.

Why Other Options Are Wrong:

• “Flip-flop is set” or “flip-flop is reset” are results, not conditions that permit change.
• “Input data has no change” directly contradicts the need for a qualifying control action.

Common Pitfalls:
Confusing edge-triggered control with level-enabled control; for gated latches, sustained enable keeps transparency, so care must be taken to avoid hazards while enabled.

Final Answer:
control input data has changed