Logic function table for the SN74LVC1G123
Most monostable multivibrator (MMV) devices have very similar logic tables to the one provided above.
The inputs A\, B, and CLR\ all trigger the same output timing circuit -- so the device can be configured to use one, two, or all three of these actively as long as all other timing specifications are followed.
For a falling-edge trigger configuration, set B = HIGH and CLR\ = HIGH and use A\ for the triggering signal.
For a rising-edge trigger configuration, set A\ = LOW and CLR\ = HIGH and use B for the triggering signal.
The CLR\ input can also be used for a rising edge trigger, with A\ = LOW and B = HIGH. The difference is that the CLR\ pin can asychronously disable the output pulse at any time, whereas the other inputs can only trigger on the appropriate rising/falling edge.