Electronic – Unclocked, edge-triggered version of RS flip-flop

flipflop

Is there such a thing as an edge-triggered RS flip-flop? That is, one input would, on rising edge, set the output to 1, and the other input would, on rising edge, set the output to 0. Falling edges would be ignored. I feel like this must exist, but I don't know what it would be called.

Best Answer

Yes, such a thing is possible, but it isn't more useful than more conventional flip-flops. Here's one way to make one:

schematic

simulate this circuit – Schematic created using CircuitLab

The output is the XOR of two internal flip-flops. If they're different, the output is high; otherwise, the output is low.

REG1 will toggle on the rising edge of the S input only if the output is low; if the output is high, it won't change state.

Similarly, REG2 will toggle on the rising edge of the R input only if the output is high; if the output is low, it won't change state.

Note that there's a requirement that near-simultaneous rising edges on both S and R have a minimum spacing, basically determined by the delay time of the feedback gates.