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.