A flip-flop (FF) is a bistable flip-flop circuit which, among other things, can store one bit in semiconductor memories. Such a digital logic circuit is used, among other things, as a bistable multivibrator in memory devices such as RAMs, shift registers and counters.
A flipflop knows two stable states, which represent the binary states "0" and "1". The states depend on the logic states at the inputs or they are changed clock-synchronously by means of triggers. In flip-flops whose states depend on the input states, the output levels are stable until the state of an input changes. The new state is then stable again.
The state change can be triggered synchronously or asynchronously by one or both pulse edges of a clock pulse. These are then referred to as state-controlled or edge-controlled flip-flops. There are also flip-flops that switch with a time delay.
A flipflop can be composed of single logics in the combination of two NOR gates or two NAND gates. In the basic circuit a flipflop has two inputs "A" and "B" and two outputs "P" and "Q".
To meet different memory device requirements, there are different flip-flop variants such as the JK flip-flop, RS flip-flop, T fl ip-flop and D flip-flop.