Dual retriggerable monostable multivibrator with reset

The 74HC123; 74HCT123 is a dual retriggerable monostable multivibrator with reset. The basic output pulse width is programmed by selection of external components (REXT and CEXT). Once triggered this basic pulse width may be extended by retriggering either of the edge triggered inputs (nA or nB). By repeating this process, the output pulse period (nQ = HIGH, nQ = LOW) can be made as long as desired. Alternatively, an output delay can be terminated at any time by a LOW-going edge on input nRD. Inputs include clamp diodes. This enables the use of current limiting resistors to interface inputs to voltages in excess of VCC.

Schmitt-trigger action in the nA and nB inputs, makes the circuit highly tolerant to slower input rise and fall times.