The '123 is a dual retriggerable monostable multivibrator capable of generating output pulses from a few nano-seconds to extremely long duration up to 100% duty cycle Each device has three inputs permitting the choice of either leading-edge or trailing edge triggering Pin (A) is an activelow transition trigger input and pin (B) is an active-high transition trigger input A low at the clear (CLR) input terminates the output pulse which also inhibits triggering An internal connection from CLR to the input gate makes it possible to trigger the circuit by a positive-going signal on CLR as shown in the truth table