At these speeds, I think I would put the uP in the loop. The problem with something that is just neg edge triggered only is that it would get tripped on each power down cycle. The unique thing about your trigger is the negative edge is followed by a positive edge in your max pulse width. You could detect the drop out with a comparator or logic gate, have this go to an interrupt and then have the uP watch for the rising edge in the right time window. Is this doable?- I don't know what you mean by "load" signal. If there's no uP, then I think some kind of more complex 555 type circuit or comparators with open collectors/open drains acting as monostables? LM393.