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Simple PWM problem ! Any ideas ?

 
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Andrew83



Joined: 16 Sep 2008
Posts: 51

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Simple PWM problem ! Any ideas ?
PostPosted: Sat Jan 17, 2009 1:27 am     Reply with quote
Hello everybody !

I have a problem with a simple PWM setup.
I'm trying to generate a 38 KHz pwm pulse, using a PIC18f452 @ 4 MHz (CCS C compiler version 4.057).
However, when i measure the pulse with PICKIT 2 logic analizer, the output doesn't correspond to 38 KHz.
Here is the output from pickit analizer :
http://rapidshare.com/files/184712495/test1.bmp.html

And here is the code of my simple application:
Code:

#include <18F452.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=4000000)

 
void main()
 {
 setup_ccp1(CCP_PWM);
 setup_timer_2(T2_DIV_BY_1, 25, 1);
 set_pwm1_duty(13);
 while(1);
  }


I've placed the capacitors as near to the crystal as possible, as it is specified in the datasheet of the pic. The values of the capacitors are correct.

What could be the problem ??

Thank you all !!
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Sat Jan 17, 2009 1:40 pm     Reply with quote
Create a simple program to toggle a pin at about 38 KHz. Use your
PicKit2 logic analyzer to see if it can read the correct frequency of the
signal on pin B0. (Or use a different pin if your hardware requires it).
Example:
Code:

// 38 KHz has a period of about 26 us. 
// Each half-cycle is about 13 us.

while(1)
  {
   output_high(PIN_B0);
   delay_us(13);
   output_low(PIN_B0);
   delay_us(13);
  }

This will tell you if your logic analyzer is working (or is configured)
correctly.
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