SR-Flipflop
The SR flip-flop, also known as a SR Latch, can be considered as one of the most basic sequential logic circuit possible. This simple flip-flop is basically a one-bit memory bistable device that has two inputs, one which will “SET” the device (meaning the output = hihg (1)), and is labelled S and another which will “RESET” the device (meaning the output = low (0)), labelled R. Then the SR description stands for “Set-Reset”. The reset input resets the flip-flop back to its original state with an output Q that will be either at a logic level “1” or logic “0” depending upon this set/reset condition.
Equation: $$Q= R'Q + R'S$$
SR flip-flop symbol
SR flip-flop circuits
SR flip-flop truth table
| CLK | S | R | Q | Q' | Description |
|---|---|---|---|---|---|
| ↑ | 0 | 0 | Q | Q' | Memory no change |
| ↑ | 0 | 1 | 0 | 1 | Reset Q » 0 |
| ↑ | 1 | 0 | 1 | 0 | Set Q » 1 |
| ↑ | 1 | 1 | X | X | Invalid |