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i cant obtain 25% duty PWM

 
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Requan



Joined: 11 May 2008
Posts: 74

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i cant obtain 25% duty PWM
PostPosted: Tue Dec 11, 2012 6:11 am     Reply with quote
Dear All,
I try to obtain 250Hz and 25% PWM, but it didn't work:
Code:

#include <18F14k22.h>
#fuses XT, NOWDT, PUT,PROTECT,NOPLLEN,BROWNOUT, BORV30, NOLVP
#use delay(clock=4M)
#define LedOK Pin_C2

void main()
{
setup_ccp1(CCP_PWM);
setup_timer_2(T2_DIV_BY_16, 249, 1); //250Hz
set_pwm1_duty(250);   //25%

set_tris_c(0x00);

   while(TRUE)
   {
      output_high(LEDOK);
      delay_ms(500);
      output_low(LEDOK);
      delay_ms(800);
   }
}


It started works from 26%:
Code:

set_pwm1_duty(260);

Could You tell me why?

Best Regards,
Martin
asmboy



Joined: 20 Nov 2007
Posts: 2128
Location: albany ny

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PostPosted: Tue Dec 11, 2012 8:35 am     Reply with quote
1024/4=???
Ttelmah



Joined: 11 Mar 2010
Posts: 19967

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PostPosted: Tue Dec 11, 2012 8:37 am     Reply with quote
1) Search the forum. In particular start with:
<http://www.ccsinfo.com/forum/viewtopic.php?t=45968&start=1>

2) Read the manual entry. What does the line:
"An 8-bit value may be used if the most significant bits are not required. " imply?.

3) What is the difference between 250, and 250L in C?.

Best Wishes
Mike Walne



Joined: 19 Feb 2004
Posts: 1785
Location: Boston Spa UK

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PostPosted: Tue Dec 11, 2012 3:07 pm     Reply with quote
This is not very helpful
Quote:
I try to obtain 250Hz and 25% PWM, but it didn't work:
I don't wish to sound rude but, I'm not a mind reader.

Tell me:-

1) What you actually got.
2) What is wrong with what you got.

Mike
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Tue Dec 11, 2012 4:13 pm     Reply with quote
Here is sample code for PWM running at 244 Hz. The duty cycle can
be changed from 0 to 100%. This is done by changing the duty cycle
value in the set_pwm1_duty() function from 0 to 255, by turning a trimpot:
http://www.ccsinfo.com/forum/viewtopic.php?t=40007&start=1
This example uses 8-bit pwm mode.
Requan



Joined: 11 May 2008
Posts: 74

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PostPosted: Wed Dec 12, 2012 1:21 pm     Reply with quote
All clear, thanks and sorry.
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