SR flip-flop
Table of contents
Introduction
SR flip-flop operates with only positive clock transitions or negative clock transitions. Whereas, SR latch operates with enable signal. The circuit diagram of SR flip-flop is shown in the following figure.
his circuit has two inputs S & R and two outputs Q(t) & Q(t)’. The operation of SR flipflop is similar to SR Latch. But, this flip-flop affects the outputs only when positive transition of the clock signal is applied instead of active enable.
State table
| S | R | Q(t+1) |
|---|---|---|
| 0 | 0 | Q(t) |
| 0 | 1 | 0 |
| 1 | 0 | 1 |
| 1 | 1 | - |
Here, Q(t) & Q(t + 1) are present state & next state respectively. So, SR flip-flop can be used for one of these three functions such as Hold, Reset & Set based on the input conditions, when positive transition of clock signal is applied.
Characteristic table
Therefore, SR Latch performs three types of functions such as Hold, Set & Reset based on the input conditions.
| S | R | Q(t) | Q(t+1) |
|---|---|---|---|
| 0 | 0 | 0 | 0 |
| 0 | 0 | 1 | 1 |
| 0 | 1 | 0 | 0 |
| 0 | 1 | 1 | 0 |
| 1 | 0 | 0 | 1 |
| 1 | 0 | 1 | 1 |
| 1 | 1 | 0 | x |
| 1 | 1 | 1 | x |
By using three variable K-Map, you can get the simplified expression for next state, Q(t + 1). The three variable K-Map for next state, Q(t + 1) is shown in the following figure.
The maximum possible groupings of adjacent ones are already shown in the figure. Therefore, the simplified expression for next state Q(t + 1) is
Q(t + 1) = S + R'.Q(t)