Flip-flop timing behavior: Generally, the hold time is short enough that the flip-flop output assumes the state dictated by synchronous control inputs just prior to the active clock edge. Evaluate the statement.

Difficulty: Easy

Correct Answer: Correct

Explanation:


Introduction / Context:
Flip-flops sample synchronous inputs (D, J/K, T with enables) around an active clock transition. Two key timing specs guarantee correct sampling: setup time and hold time. This item checks your understanding of how short hold time supports correct state capture.



Given Data / Assumptions:

  • Synchronous inputs satisfy setup time (stable before clock edge).
  • Hold time is small but nonzero (must remain stable briefly after the edge).
  • Active edge could be rising or falling, depending on the device.


Concept / Approach:
If inputs meet setup and hold, the device samples reliably at the active edge and the output transitions to the state commanded by those inputs. Many modern flip-flops specify minimal or even zero hold time thanks to internal clocking schemes, which aligns with the statement’s “generally short enough.”



Step-by-Step Solution:

Ensure synchronous inputs are valid and stable for at least t_setup before the active edge.Maintain inputs stable for at least t_hold after the edge.Given small t_hold, the output resolves to the state defined immediately prior to the edge.Therefore, the statement is correct under standard timing practice.


Verification / Alternative check:
Consult device timing diagrams: the sampling instant is at the active edge, and output changes after t_co (clock-to-output delay) when setup/hold are met.



Why Other Options Are Wrong:

Incorrect: Conflicts with basic edge-triggered sampling behavior.True only for asynchronous inputs: Asynchronous inputs are not governed by setup/hold in the same way and can violate metastability rules.True only for negative-edge devices: Applies to either edge; polarity is irrelevant.


Common Pitfalls:
Ignoring hold time because it is “small”; changing inputs right at the edge; mixing asynchronous set/reset with synchronous data timing.


Final Answer:
Correct

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