SN74LS221N (TEXAS INSTRUMENTS)

The SN74LS221N is a dual Monostable Multivibrator with schmitt-trigger inputs. Its performance characteristics virtually identical to those of the '121 devices. Each multivibrator features a negative-transition- triggered input and a positive-transition-triggered input, either of which can be used as an inhibit input. Pulse triggering occurs at a particular voltage level and is not directly related to the transition time of the input pulse. Schmitt-trigger input circuitry for B input allows jitter-free triggering from inputs with transition rates as slow as 1V/s, providing the circuit with excellent noise immunity, typically of 1.2V. A high immunity to VCC noise, typically of 1.5V, is also provided by internal latching circuitry. Once fired, the outputs are independent of further transitions of the A and B inputs and are a function of the timing components or the output pulses can be terminated by the overriding clear. Input pulses can be of any duration relative to the output pulse.