# SN74LVC1G123 Monostable Multivibrator IC

Good afternoon,

I was hoping someone could help me understand some of the terminology in this data sheet and how I translate that into a basic one-shot multivibrator that is retriggerable.

Page 11-13 are the description and application portion of the datasheet. My questions are

1)The pins A and B, and how you work with them to trigger the one-shot. My interpretation is that either A or B must be brought HIGH by a transient signal and the other must be LO(grounded) to trigger the one-shot.

2)the term "gated" with regards to retriggering the one-shot while it is still HI to extend the duty cycle by restarting the RC constant (how to retrigger the one-shot before the duty cycle ends).

Any help in understanding the involved circuitry would be greatly appreciated.

Thank you!

• The reset must be high. If it is, and if A and B are high, then bringing A low will trigger. If A and B are low, bringing B high will trigger. Doing either of these while the output is active (in the middle of an output pulse) will extend the output pulse by the nominal pulse width. Mar 7, 2017 at 22:28
• Is the CLR pin what you are calling the "reset"? Mar 7, 2017 at 22:39
• Yes. CLR stands for "clear". Also known as reset. Same function is called MR (master reset) on some counters and shift registers. Mar 7, 2017 at 23:28
• – CL.
Mar 8, 2017 at 10:02

The term "gated" simply means that their are two inputs, $\small \overline{\text{A}}$ and B, only one of which can be used at a given time -- one input acts as a enable (gate) for the other. If B is held high, then the '123 one-shot is triggered by a falling edge pulse on $\small \overline{\text{A}}$. If $\small \overline{\text{A}}$ is held low, then the '123 one-shot is triggered by a rising edge pulse on B.
In either case, the reset line $\small \overline{\text{CLR}}$ must be held high. If it goes low, then any output timing is prematurely reset.
While output timing is active, if the input $\small \overline{\text{A}}$ or B is triggered again, then the output is extended for a full-time period from that point, which is what is meant by being retriggerable.