74LV123PW,118

The 74LV123PW is a dual Si-gate CMOS retriggerable Monostable Multivibrator with reset. It is pin and function compatible with the 74HC123 and 74HCT123. It uses three methods to control the output pulse width, first - The basic pulse time is programmed by the selection of an external resistor (REXT) and capacitor (CEXT). These are normally connected. Second - once triggered, the basic output pulse width may be extended by retriggering the gated active low-going edge input (nA) or the active high-going edge input (nB). By repeating this process, the output pulse period (nQ = high, nQ = low) can be made as long as desired. Third - alternatively, an output delay can be terminated at any time by a low-going edge on input nRD, which also inhibits the triggering. Schmitt-trigger action in the nA and nB inputs makes the circuit highly tolerant of slower input rise and fall times.