PIC18F2620 CCP Double Edge Triggering

[jmb1539]

I'm using a PIC18F2620 to measure a frequency of an incoming signal consisting of a 5V - 0V square wave. My CCP1 is setup for capture mode falling edge detection. While running, I'm getting an occasional interrupt on the falling edge (as I should) and the rising edge (should not happen) of the incoming signal. Sometimes this happens more frequently, and at other times it happens less frequently. I verified the double edge triggering by toggling an output every time the interrupt is generated and observing it on a scope.

Has anyone seen this before or read about it in any errata? Does anyone know a work around?

Thanks,

JuBo

[PCM programmer]

How clean is the input signal ? Does it have noise on the edges ?
You could put in an RC filter (low pass) to remove the noise.
Try the circuit below. This gives a cutoff frequency of 159 KHz.
You didn't say what your input signal frequency is. But I think
this would be worth trying, at least initially.

[jmb1539]

My frequency input is in the range of 3-50Hz. It was a bit unstable, so I passed it through a schmit trigger to square off the signal. This really cleaned it up, but I was still getting a trigger on both edges of the input signal. I went and installed a 70Hz RC filter on the output of the schmit trigger and this really seems to have stabilized the interrupts. I guess there was enough instability on the schmit trigger transition that it caused an interrupt to be serviced by the PIC. Once again, thanks for your help.

JuBo