74HC123
74HC123 is Dual retriggerable monostable multivibrator manufactured by Philips Semiconductors.
FEATURES
- DC triggered from active HIGH or active LOW inputs
- Retriggerable for very long pulses up to 100% duty factor
- Direct reset terminates output pulse
- Schmitt-trigger action on all inputs except for the reset input
- Output capability: standard (except for n REXT/CEXT)
- ICC category: MSI GENERAL DESCRIPTION
The 74HC/HCT123 are high-speed Si-gate CMOS devices and are pin patible with low power Schottky TTL (LSTTL). They are specified in pliance with JEDEC standard no. 7A. The 74HC/HCT123 are dual retriggerable monostable multivibrators with output pulse width control by three methods. The basic pulse time is programmed by selection of an external resistor (REXT) and capacitor (CEXT). The external resistor and capacitor are normally connected as shown in Fig.6. Once triggered, the basic output pulse width may be extended by retriggering the gated active LOW-going edge input (n A) or the active HIGH-going edge input (n B). By repeating this process, the output pulse period (n Q = HIGH, n Q = 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 n RD, which also inhibits the triggering. An internal connection from n RD to the input gates makes it possible to trigger the circuit by a positive-going signal at input n RD as shown in the function table. Figures 7 and 8 illustrate pulse control by retriggering 1998 Jul 08 2 QUICK REFERENCE DATA GND = 0 V; Tamb = 25 °C; tr = tf = 6 ns and early reset. The basic output pulse width is essentially determined by the values of the external timing ponents REXT and CEXT. For pulse widths, when CEXT < 10 000 p F, see Fig.9. When CEXT > 10 000 p F, the typical output pulse width is defined as: t W = 0.45 × REXT × CEXT (typ.),
74HC/HCT123 where: t W = pulse width in ns; REXT = external resistor in kΩ; CEXT = external capacitor in p F. Schmitt-trigger action in the n A and n B inputs, makes the circuit highly tolerant to slower input rise and fall times. The ‘123’...
