Hi,Kevj

That's quite simple : the datas from µChip give a minimum transition time the PIC can see on its inputs ... whether the clock frequency.

Ioannis gave you the link to AN592 that uses this feature of their chips; I cant tell you it works well, and 50Mhz input frequency is a minimum ... ( If PCB is well designed ... LOL !!! )

Now, understand you won't READ the spike length, but only "FLAG" it

if you want to catch much shorter events, You probably can use some Very High speed TTL ( or CMOS ? ) monostable to lengthen the spike ... once more, it will only be a spike "flagging" ....

Alain