DatasheetCafe

These d-c triggered multivibrators feature output pulse-duration control by three methods. The basic pulse time is programmed by selection of external resistance and capacitance values (see typical application data). The ‘122 and ‘LS122 have internal timing resistors that allow the circuits to be used with only an external capacitor, if so desired. Once triggered, the basic pulse duration may be extended by retriggering the gated low-level-active (A) or high-level-active (B) inputs, or be reduced by  se of the overriding clear.

Features

1. D-C Triggered from Active-High or Active-Low Gated Logic Inputs
2. Retriggerable for Very Long Output Pulses, Up to 100% Duty Cycle
3. Overriding Clear Terminates Output Pulse

Official Homepage : http://www.ti.com/product/SN54LS123