Positive edge-triggered flip-flop behavior — when are inputs sampled? A positive edge-triggered flip-flop changes state only at the active (rising) clock transition. Complete the statement: “A positive edge-triggered flip-flop will accept (sample) inputs only when the clock …”

Introduction / Context:
Synchronous sequential circuits rely on edge-triggered flip-flops to register data at precise instants. Understanding exactly when a positive edge-triggered flip-flop samples its inputs is crucial for proper timing closure, meeting setup/hold times, and avoiding metastability in digital systems.

Given Data / Assumptions:

• The device is a positive edge-triggered flip-flop (for instance, a D or J-K with a positive edge clock).
• Setup time (tsu) and hold time (th) constraints must be satisfied around the sampling edge.
• Asynchronous controls, if any, are inactive and do not influence the normal sampling behavior.

Concept / Approach:
By definition, a positive edge-triggered flip-flop samples its inputs at the instant the clock transitions from LOW to HIGH. Data present at the input must be stable for a window that starts tsu before the edge and continues through th after the edge. The output Q updates as a result of this sampling and remains stable until the next active edge (ignoring asynchronous overrides).

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