how to measure frequency...

[PCM programmer]

His question is really, can he use the Timer1 oscillator with an external
crystal in the CCP capture mode ? I tried experimenting with this a
few days or weeks ago, while reading one of his previous threads, and
I couldn't make it work. It would not capture. Switching to an internal
clock for Timer1 caused it to capture.

The 16F917 data sheet says this:

[RLScott]

Then here is what he can do. Forget about input capture mode. Use the frequency to be measured to generate an interrupt, either on RB0 or on some other interrupt-on-change input. Then in the ISR, read Timer 1. This will be just as good as input capture since 32kHz gives 30 microseconds between ticks. Therefore the interrupt latency is less than one tick.

Robert Scott
Real-Time Specialties

[deepakomanna]

[RLScott]

Since you have not told us which PIC you are using, I have no idea what functions are on RC5, RE3, RA7 and RA6. But if one of these is an input capture pin, perhaps the input capture interrupt will work even if the loading of the PR register does not. In that case you can use the interrupt to read Timer 1 yourself. If this interrupt does not work when Timer 1 is asynchronous, then you are out of luck.

Robert Scott
Real-Time Specialties

[Kenny]

Options are limited. I too experimented with the capture (on a different pic) and got some odd results.

Could just use timer 1 as a counter for the input signal on the T1CKI pin (RC5 if it's the 16F917), and count for one second.
The count is the frequency in Hz if the counter was cleared first.
Use
setup_timer_1(T1_EXTERNAL|T1_DIV_BY_1);

Another timer, timer 0 or timer 2, could be used for timing the one second. Timer 2 is convenient for this purpose.

eg with
setup_timer_2(T2_DIV_BY_16,249,10);
the timer 2 interrupt will occur every 20mS. In the timer 2 interrupt service routine count the interrupts,
and when 50 have occurred get the count from timer 1. Set a flag for main() to display the count.

Accuracy would be 1Hz at the 10 Hz end of the input range, and within the accuracy limits of the internal 8MHz RC oscillator higher up the range.