SR flip-flop
(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 {race
condition} occurs and the outputs will be in an indeterminate
state. A {JK flip-flop} avoids this possibility.
{(http://www.play-hookey.com/digital/logic4.html)}.
(1997-05-15)