piclist-bounces@mit.edu wrote:
> I'm looking for a 555-based monostable (one-shot) circuit
> whose output will STAY high as long as short negative-going
> pulses are present at the input.

I think the 74HC123 will do this. Once triggered, the output pulse can
be extended by retriggering. IIRC, it can be configured for either
positive or negative pulses.

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