The universal flip-flop. J=K=1 toggles — no forbidden state.
Change the inputs as often as you like between edges — the flip-flop only looks at them at the rising edge ▲. The dots on the timing diagram mark what it saw.
| J | K | Q next | Action |
|---|---|---|---|
| 0 | 0 | 0 | hold |
| 0 | 1 | 0 | reset |
| 1 | 0 | 1 | set |
| 1 | 1 | 1 | toggle |