74HCT423

The 74HCT423 is high-speed Si-gate CMOS devices and are pin compatible with low power Schottky TTL (LSTTL). They are specified in compliance with JEDEC standard no. 7A.

The 74HCT423 is dual retriggerable monostable multivibrators with output pulse width control by two methods. The basic pulse time is programmed by selection of an external resistor (RE_XT) and capacitor(CE_XT). The external resistor and capacitor are normally connected as shown in Fig.6.

Once triggered, the basic output pulse of the 74HCT423 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. When nRD is LOW, it forces the nQ output LOW, the nQ output HIGH and also inhibits the triggering.

Figures 7 and 8 illustrate pulse of the 74HCT423 control by reset. The basic output pulse width is essentially determined by the values of the external timing components RE_XT and CE_XT. For pulse widths, when CE_XT < 10 000 pF, see Fig.9. When CE_XT > 10 000 pF, the typical output pulse width is defined as:tW = 0.45 * RE_XT * CE_XT (typ.), where, tW = pulse width in ns; RE_XT = external resistor in kW; CE_XT = external capacitor in pF. Schmitt-trigger action in the nA and nB inputs, makes the circuit highly tolerant to slower input rise and fall times.

The "423" is identical to the "123" but cannot be triggered via the reset input.