Asynchronous control of a J–K flip-flop: Which statement best characterizes the preset/clear (asynchronous) inputs on a J–K flip-flop?

Introduction / Context:
Flip-flops often include asynchronous control inputs such as preset (PRE/SET) and clear (CLR/RESET). These inputs override the synchronous data path and are essential for initialization, fault recovery, and forcing known states. Understanding their priority and timing relative to the clock is fundamental for robust sequential design.

Given Data / Assumptions:

• Device: J–K edge-triggered flip-flop with asynchronous PRE and CLR.
• Active level may be low or high depending on the family, but the logical effect is the same.
• Design goal: deterministic initialization and override behavior.

Concept / Approach:
Asynchronous inputs act immediately when asserted, independent of the clock. They also have higher priority than synchronous inputs (J and K), ensuring that when PRE or CLR is asserted, the output goes to the prescribed state regardless of upcoming clock edges. Good practice avoids asserting both active levels simultaneously, which could produce an invalid or unpredictable state.

Step-by-Step Solution:

Verification / Alternative check:
Datasheet truth tables show that asserting PRE or CLR immediately drives Q, and notes warn against simultaneous activation. Timing diagrams confirm no clock is required for their effect.

Why Other Options Are Wrong:

• Any single statement alone is incomplete; all are true together, making “all of the above” correct.
• “Affect output only after two clock cycles” is false; asynchronous means no clock is required.

Common Pitfalls:
Tying PRE and CLR together; forgetting they are often active-low; violating recovery/removal times, which can cause unpredictable behavior when releasing asynchronous signals near clock edges.

Final Answer:
all of the above