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Thread: Need help using capture inputs on 16F877
face BY : Dan Michaels email (remove spam text)

Fred Bailey wrote:
>I'm having trouble with the capture input CCP1. I have capture input CCP2
>working (finally).
>I have tested the Port C - I/O by disabling both capture modules and reading
>port C.
> All bits work OK (Hi and Low). But, I can't get CCP1 (RC2 input) to capture. I
>have also tried
>using CCP1 and CCP2 together and separately Only CCP2 works.
>I initialize the CCP1 as follows:
>Setup_capture  ; RC1input pulse, 50uSec wide every 16.6mSec, use capture2
{Quote hidden}

Hi Fred, I have some suggestions here.

1 - I don't see you configuring the port direction bits.

2 - I don't see you doing a global interrupt enable, or resetting
   the relevant intr flag.

3 - I would not turn on Timer 1 until everything else was setup and ready
   to go. You do this in your first couple statements.

4 - Timer 1 is going to clock out very fast, probably < 1 sec, depending
   upon the xtal in use, so you have to get right on the job with your
   input signal soon as you run this code, else you will miss the event.

5 - You also have to jump thru a few hoops in order to avoid false captures,
   as detailed in the spec sheet.

6 - During development, I would first get this code working correctly
   in polled mode rather than interrupt mode - ie, simply poll the
   interrupt flag, and read the register. Fewer things to get confused

hope this helps,
- dan michaels

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Subject (change) Need help using capture inputs on 16F877

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