When the clock input on the JK flip-flop changes from '0' to '1', the 'Q' and '~Q' outputs change according to the state of the 'J' and 'K' inputs.
The device acts as a latch, so that the 'J' and 'K' inputs may change but the output remains constant until the next clock edge.
You can use Set ('S') and Reset ('R') control pins to put the output in a predefined state.
Truth table:
| J | K | Q | ~Q |
|---|---|---|---|
| 0 | 0 | unchanged | unchanged |
| 0 | 1 | 0 | 1 |
| 1 | 0 | 1 | 0 |
| 1 | 1 | toggle | toggle |