Introduction / Context:
The S-R storage primitive is simple but suffers from a forbidden input combination that complicates reliable operation. The J-K flip-flop generalizes S-R behavior to remove this invalid case, making it highly useful in synchronous counters and finite-state machines.
Given Data / Assumptions:
- S-R latch/flip-flop has a forbidden state (S=R=1 for NOR, or S̅=R̅=0 for NAND versions).
- J-K flip-flop introduces inputs J and K that map to set, reset, hold, and toggle behaviors under clock control.
- We compare device properties for robust synchronous design.
Concept / Approach:
The hallmark of the J-K is that the “both inputs asserted” case is defined as toggle, not forbidden. Thus, there is no invalid input combination in normal synchronous operation, provided setup/hold are met. This clears a major usability hurdle present with S-R devices.
Step-by-Step Solution:
Map S-R caveat: S=R=1 produces an illegal state (for NOR implementation).Map J-K behavior: J=1, K=1 → toggle at the active clock edge (Q(next)=Q’).Implication: J-K safely supports all input combinations, hence “no invalid states.”
Verification / Alternative check:
Examine truth tables: S-R has a forbidden row; J-K has a defined action for every row.
Why Other Options Are Wrong:
it has fewer gates: Often more complex than S-R; not the advantage.it has only one output: J-K devices present Q and Q’ like others.it does not require a clock input: J-K flip-flops are typically clocked.
Common Pitfalls:
Assuming “toggle” means asynchronous behavior; toggling is clocked.Confusing latches with edge-triggered flip-flops.
Final Answer:
it has no invalid states
Discussion & Comments