Low frequency measurement for a PIC

The system based on a 16f877a is operational. It is used to make an automatic start of a diesel generator to recharge the batteries on my boat. I would like to add an action that will be initiated by the frequency of a pulse generated by a reed switch that would be installed near a pulley with a small magnet
The frequency at witch I would want a trigger is when it excedeed 6 to 7 Hz at a certain point where it would indicate that the rpm is now above 800rpm at the crankshaft.
This is to tell the controller that the engine is started and accellerating and therefore, to stop the starter. At this time, it is done by the oil pressure and limited by a 3 seconds interval. This is not satisfactory. Many missed starts...

Thanks in advance for any help.

you can set up a timer that can count pulses on PortA.4 and delay for one second then read the value that is on Timer0.

have a look here

thanks
I did it and it works