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How to use 8 Mhz clock to generate slow PWM Frequencies

 
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Brian



Joined: 29 Jun 2010
Posts: 10

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How to use 8 Mhz clock to generate slow PWM Frequencies
PostPosted: Mon Aug 30, 2010 1:30 pm     Reply with quote

Hi,

I am using the PIC18F2480 and one of the goals of my project is to output PWM signals with slow frequencies (between 10 - 100 Hz). I know how to accomplish this through setting the internal oscillator frequency much lower (125Khz or 250Khz); however, I would like to be able to use the normal 8 Mhz clock frequency or somewhere in the Mhz range.

Would it be possible to hook up a slow external crystal or oscillator for the timer to use to generate the PWM signals, but to run the main program from the internal 8 Mhz clock? Or are there any other ways to accomplish this?

Thanks.

Here's some sample code I'm using to generate, if it helps:
Code:


void main()
{
    setup_oscillator(OSC_125KHZ);

   
   setup_timer_2(T2_DIV_BY_16, 255, 1);   
   setup_ccp1(CCP_PWM);

       while(1)
       {
        set_pwm1_duty(395L);
       }
}

PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Mon Aug 30, 2010 1:36 pm     Reply with quote

Look at the software PWM routines in this thread, using #int_rtcc (Timer0):
http://www.ccsinfo.com/forum/viewtopic.php?t=37807
Brian



Joined: 29 Jun 2010
Posts: 10

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PostPosted: Tue Aug 31, 2010 1:28 pm     Reply with quote

Thanks very much. I posted an additional question on one of the threads already created here:

http://www.ccsinfo.com/forum/viewtopic.php?p=137266#137266

Thanks.
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