Unclocked, edge-triggered version of RS flip-flop?
Yes, such a thing is possible, but it isn't more useful than more conventional flip-flops. Here's one way to make one:







simulate this circuit &ndash; 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.