555/556 Bistable (flip-flop) circuit

555/556 Bistable (flip-flop) - a memory circuit

555 bistable circuit

The circuit is called a bistable because it is stable in two states: output high and output low. It is also known as a 'flip-flop'. It has two inputs:

• Trigger (555 pin 2) makes the output high.
  Trigger is 'active low', it functions when < ¹/₃ Vs.
• Reset (555 pin 4) makes the output low.
  Reset is 'active low', it resets when < 0.7V.

The power-on reset, power-on trigger and edge-triggering circuits can all be used as described above for the monostable.