Flip-flop (electronics)

In electronics, flip-flops and latches are circuits that have two stable states that can store state information – a bistable multivibrator. The circuit can be made to change state by signals applied to one or more control inputs and will output its state (often along with its logical complement too). It is the basic storage element in sequential logic. Flip-flops and latches are fundamental building blocks of digital electronics systems used in computers, communications, and many other types of systems. Flip-flops and latches are used as data storage elements to store a single bit (binary digit) of data; one of its two states represents a "one" and the other represents a "zero". Such data storage can be used for storage of state, and such a circuit is described as sequential logic in electronics. When used in a finite-state machine, the output and next state depend not only on its current input, but also on its current state (and hence, previous inputs). It can also be used for counting of pulses, and for synchronizing variably-timed input signals to some reference timing signal. The term flip-flop has historically referred generically to both level-triggered (asynchronous, transparent, or opaque) and edge-triggered (synchronous, or clocked) circuits that store a single bit of data using gates. Modern authors reserve the term flip-flop exclusively for edge-triggered storage elements and latches for level-triggered ones. The terms "edge-triggered", and "level-triggered" may be used to avoid ambiguity. When a level-triggered latch is enabled it becomes transparent, but an edge-triggered flip-flop's output only changes on a clock edge (either positive going or negative going). Different types of flip-flops and latches are available as integrated circuits, usually with multiple elements per chip. For example, 74HC75 is a quadruple transparent latch in the 7400 series. The first electronic latch was invented in 1918 by the British physicists William Eccles and F. W. Jordan.