U74HC123

DESCRIPTION 

The U74HC123 is high-speed Si-gate CMOS device and is pin 

compatible with low power Schottky TTL (LSTTL). 

The U74HC123 is a dual retriggerable monostable 

multivibrator with output pulse width control by three methods.

The basic pulse time is programmed by selection of an external 

resistor (REXT) and capacitor (CEXT). 

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 (nB). By repeating this process,

the output pulse period (nQ=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 nR , which also inhibits 

the triggering. 

An internal connection from nR to the input gates makes it D possible 

to trigger the circuit by a positive-going signal at input nR as shown in 

the function table. The basic out D put pulse width is essentially determined 

by the values of the external timing components REXT and CEXT. 

Schmitt-trigger action in the n A and nB inputs, makes the circuit highly 

tolerant to slower input rise and fall times. 

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

规格书U74HC123