SR flip-flop

hardware (Or "RS flip-flop") A "set/reset" flip-flop in

which activating the "S" input will switch it to one stable

state and activating the "R" input will switch it to the other

state.

The outputs of a basic SR flip-flop change whenever its R or S

inputs change appropriately. A clocked SR flip-flop has an

extra clock input which enables or disables the other two

inputs. When they are disabled the outputs remain constant.

If we connect two clocked SR flip-flops so that the Q and /Q

outputs of the first, "master" flip-flop drive the S and R

inputs of the second, "slave" flip-flop, and we drive the

slave's clock input with an inverted version of the master's

clock, then we have an edge-triggered RS flip-flop. The

external R and S inputs of this device are latched on one edge

(transition) of the clock (e.g. the falling edge) and the

outputs will only change on the next opposite (rising) edge.

If both R and S inputs are active (when enabled), a racecondition occurs and the outputs will be in an indeterminate

state. A JK flip-flop avoids this possibility.

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(1997-05-15)