Hi!!

Has anyone ported the frecuency counter application note from
microchip to
16x84?...

I havent looked at that appnote, but I did build a counter described
by Halicky which works perfectly on a 16F84. I redesigned the
frontend to get more sensitivity, but if you arent interested in
millivolt levels, his original design is fine. Here is a link. If you have
trouble getting the files, let me know.

http://www.qsl.net/ta1dr/fm.htm