How Do Integrated Flip-Flop Circuits Work?

The 7474 integrated circuit has two flip-flops.

Integrated circuit (IC) flip-flops, such as the 7474, serve as simple electronic memory units. They have two stable states, either on or off, storing one binary bit of information. Because the flip-flop is a simple circuit, the 7474 contains two of them.

Inputs

A basic flip-flop has two inputs. Normally, the inputs, set and reset, are at a low voltage, nominally zero volts. If you apply a "high" DC voltage (about 5 volts) to the set input, the flip-flop's output also goes high and will stay that way until you turn the reset input high.

Outputs

The flip-flop has two outputs: a main output and its complement. When the main output goes high, the complement output goes low and vice-versa.

Other Inputs

Real-world ICs, such as the 7474, have two extra inputs: clock and data. For the output to go high, clock, data and set all must be high. This makes the flip-flop more useful as a binary memory circuit.

Forbidden State

If you apply a high signal to both the set and reset inputs, this normally drives both outputs low. This does not damage the flip-flop, but you should avoid this situation to keep the circuit's logic consistent.

References

• Electronics Tutorials: Edge-Triggered Latches: Flip-Flops
• NXP: 74F74 Flip Flop IC
• All About Circuits: The S-R Latch