200mV is inadquate for direct connection to a PIC - UNLESS you have built-in Comparators. Set your VRef to trip say at 100mV, use the option to feedback the Comparator Output to the pin you will be taking the measurements with Count. Refer to your PIC's Datasheet on how to do this.

You have an error in your code... remove the comma from the line...

IF F=1000 THEN,OK

If you are using a PIC as a 1kHz detector... it's probably cheaper to use an NE567.