Welcome, dave ...

There might be a joke: the Hi 200 µs part is always the same value ...so, may be it is not compulsory to MEASURE it, just verify its presence ... ( no change for 150µs, for instance ...)

a simple PULSIN input, 0, value could do the work ... and catch all the incoming pulses !!!

a small mistake, in the lines:

PULSE = (Highpart + Lowpart) * 10 'pulse width in us

as resolution is 2µs @ 20 Mhz ... you should write:

PULSE = (Highpart + Lowpart) * 2 'pulse width in us

Alain