SR flip-flop

SR flip-flop

(hardware)(Or "RS flip-flop") A "set/reset" flip-flop inwhich activating the "S" input will switch it to one stablestate and activating the "R" input will switch it to the otherstate.

The outputs of a basic SR flip-flop change whenever its R or Sinputs change appropriately. A clocked SR flip-flop has anextra clock input which enables or disables the other twoinputs. When they are disabled the outputs remain constant.

If we connect two clocked SR flip-flops so that the Q and /Qoutputs of the first, "master" flip-flop drive the S and Rinputs of the second, "slave" flip-flop, and we drive theslave's clock input with an inverted version of the master'sclock, then we have an edge-triggered RS flip-flop. Theexternal R and S inputs of this device are latched on one edge(transition) of the clock (e.g. the falling edge) and theoutputs will only change on the next opposite (rising) edge.

If both R and S inputs are active (when enabled), a race condition occurs and the outputs will be in an indeterminatestate. A JK flip-flop avoids this possibility.

http://play-hookey.com/digital/logic4.html.