JK flip-flop
JK flip-flop: like RS, but J=K=1 toggles instead of being forbidden.
Characteristic table (on the CLK 0→1 edge)
| J | K | Q⁺ |
|---|---|---|
| 0 | 0 | Q (hold) |
| 0 | 1 | 0 |
| 1 | 0 | 1 |
| 1 | 1 | Q̄ (toggle) |
Pins
J, K and CLK on the left; Q and its complement Q̅ on the right.
How to use it
Tie J and K to 1 and it becomes a T flip-flop — the classic building block of synchronous counters.
Usage example
Switches J and K plus a clock go on the left. With J = K = 1, Q flips on every tick; otherwise it behaves like an RS flip-flop.
Common mistakes
Q only changes when CLK goes from 0 to 1 — drive CLK with a clock or flip a switch by hand.