The simplest form is the RS flip-flop; an implementation using NAND gates is shown in the diagram together with the flip-flop's truth table. A logic 1 on one of the two inputs either sets the Q output to logic 1 or resets Q to logic 0. Output Q̄ is the logical complement of Q. When R̄ and S̄ are both logic 1 (which is equivalent to R and S both logic 0), Q does not change state. The situation of both R̄ and S̄ at logic 0 is ambiguous and is avoided in more complex flip-flop implementations (see JK flip-flop). The outputs of this (and other) flip-flops are not just functions of the inputs but depend on both inputs and outputs. The device is thus a simple sequential circuit.
Extra logic gating may be included in the RS device, and in more complex flip-flops, to allow a clock signal to be input to the flip-flop, so producing a clocked flip-flop (see clock). The Q output will not then change state until an active edge of the clock pulse occurs (edge-triggered device) or a complete clock cycle has occurred (pulse-triggered device). Provision may also be made to set up a given output regardless of the state of the inputs.
Various forms of flip-flop are available to perform specific functions; these include JK, D, T, and master-slave flip-flops. Flip-flops are important as memory devices in digital counters. The RS flip-flop is often considered to be the universal flip-flop since it forms the basic building block for more sophisticated implementations. JK, master-slave, and D flip-flops are all available in the standard TTL and CMOS series of integrated-circuit components.
flip-flop • n. 1. a light sandal, typically of plastic or rubber, with a thong between the big and second toe. 2. a backward somersault or handspring. 3. inf. an abrupt reversal of policy: his flip-flop on taxes. 4. Electr. a switching circuit that works by changing from one stable state to another, or through an unstable state back to its stable state, in response to a triggering pulse. • v. [intr.] 1. move with a flapping sound or motion: she flip-flopped off the porch in battered sneakers. 2. perform a backward somersault or handspring: fig. Julie's stomach flip-flopped. 3. inf. make an abrupt reversal of policy: the candidate flip-flopped on a number of issues.