frequency counter circuit problem

[ahmad-al3omar]

dear friends;
i am using pic16f877a to count frequency by using the external interrupt and the timer1 , and i have my circuit which out a pulses with peak 5v
the problem is when i mesure the pulses by the Oscilloscope the pulses is good but when i connect the output of the pulsating circuit to the PIC the Oscilloscopes reading goes to zero , the simulation of the prgram is running greatfully ,, second problem if i dont connect any thing to the Interrupt pin , i read on the LCD a very huge number from where i dont know! so i have to put a capacitor to set it to zero.

please help me to find out where are my faults and errors??
thank you
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A.T.N

[SherpaDoug]

If the scope signal goes to zero when you connect the PIC it implies the PIC pin is set to be an output. Either that or you have some weird grounding problem, like the two leads from the signal source are reversed.
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