RS flip-flop
RS flip-flop: S=1 sets Q to 1, R=1 resets it to 0, both 0 holds.
Characteristic table (on the CLK 0→1 edge)
| S | R | Q⁺ |
|---|---|---|
| 0 | 0 | Q (hold) |
| 0 | 1 | 0 |
| 1 | 0 | 1 |
| 1 | 1 | not allowed (kept unchanged here) |
Pins
S, R and CLK on the left; Q and its complement Q̅ on the right.
How to use it
Remember whether something happened, like a lamp that stays on after one button press until reset.
Usage example
Switches S and R plus a clock go on the left, Q drives an LED. On a rising edge: S = 1 sets, R = 1 resets, both 0 holds.
Common mistakes
S and R both 1 is not allowed. Also, Q only changes at the instant CLK goes from 0 to 1.