JK flip-flop truth table — identify the “no change” input condition For a JK flip-flop, which input combination leaves the current state unchanged on the active clock edge?

Introduction / Context:
The JK flip-flop generalizes the SR flip-flop by resolving the forbidden input while providing useful functions—set, reset, toggle, and hold—via different input combinations. Recognizing the “no change” condition is essential when designing counters and state machines that must preserve state under certain inputs.

Given Data / Assumptions:

• Synchronous edge-triggered JK flip-flop behavior is assumed.
• Inputs J and K are sampled on the active clock edge.
• Asynchronous preset/clear (if present) are inactive.

Concept / Approach:
The canonical JK truth table is: J=0,K=0 → no change (hold); J=0,K=1 → reset (Q←0); J=1,K=0 → set (Q←1); J=1,K=1 → toggle (Q←/Q). Thus the specific “no change” case is J=0 and K=0.

Step-by-Step Solution:

Verification / Alternative check:
Examine a vendor timing diagram; with J=K=0 at the clock edge, Q follows its previous value with no transition, confirming the hold behavior. HDL simulation with a JK primitive (or a behavioral model) will show the same.

Why Other Options Are Wrong:

• J=1,K=1: toggles, not hold.
• J=1,K=0: sets Q=1.
• J=0,K=1: resets Q=0.
• J=X,K=X: not a defined, guaranteed hold condition; behavior depends on specific X values.

Common Pitfalls:

• Assuming J=K=1 is a hold; it is the toggle case for JK.

Final Answer:
J = 0, K = 0