# 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. – WhatRoughBeast Mar 7 '17 at 22:28
• Is the CLR pin what you are calling the "reset"? – LevyDee Mar 7 '17 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. – WhatRoughBeast Mar 7 '17 at 23:28
• – CL. Mar 8 '17 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.