From: Harold Hallikainen <harold@mai.hallikainen.org>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Thu, 17 Sep 2020 20:27:34 -0700
Subject: Re: [PIC] Compare Mode
Thread-Topic: [PIC] Compare Mode
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This sounds like a phase control light dimmer! I did a four channel one
with a single CCP register, figuring out which triac I needed to turn on
first, loading the CCP register with that value, then when I got the
interrupt, turned on the triac and loaded the CCP register with the next
value I needed. I have not looked at that in a long time (more than 10
years). I think I started with a 17C42 and ended up using an 18F452. If
indeed you're doing a light dimmer, I'd load the CCP registers and clear
the timer, and turn off the outputs on a zero cross. Then each CCP
interrupt would turn on an output and clear the interrupt flag.

This is probably not much help since it's been more than 10 years since I
worked on it.

Good luck!

Harold


> I have a PIC16F1828 running from the internal 4MHz oscillator. I use the
> various timers regulatly, but don't recall using the CCP modules before.
> I'm using MPLABX and XC8.
>
> There is a 100Hz interrupt (INT0) from an optocoupler for zero cross
> sync. I've set timer 1 to Fosc/4 and no prescaler, so that should be
> ticking over at 1us increments. I'm trying to use CCP1, CCP2 and CCP3 to
> get an interrupt at three different points from the zero cross interrupt.
>
> CCP1CON is set to 0x0A (compare with interrupt) and CCPR1 is set to 5000
> (decimal) when the INT0 interrupt occurs. I'm clearing a pin when INT0
> occurs and setting it when the CCP1IF interrupt is serviced.
>
> I'm getting a much longer period (LED off time) than the 5ms I expected.
> The timing is not even proportional to the values I enter. Am I missing
> something fundamental about how CCP works?
>
> David...
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>


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