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affonso.industra
Joined: 31 Jan 2013
Posts: 6
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| PWM Trouble - PIC24EP512GU810 with CCS |
 Posted: Thu Mar 21, 2013 12:04 pm |
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Hello,
I'm facing some troubles to put PWM module of PIC24EP512GU810 to work: it works fine, but I can't change its frequency!!
Here is the code:
| Code: |
#include <24EP512GU810.h>
#fuses HS,NOPROTECT,NOWDT, NOALTI2C2
#use delay(clock = 140000000, crystal=20000000)
#pin_select OC1=PIN_G15
...
main()
{
...
setup_compare(1, COMPARE_PWM_EDGE | COMPARE_TIMER2);
setup_timer2(TMR_INTERNAL | TMR_DIV_BY_1, 0xFFC0);
set_pwm_duty(1,32736);
while(1);
}
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With this code I have a PWM with frequency of 1.069 kHz and duty = 50%. In fact the frequency is correct: (140 MHz / 2) * (1) / (65473) = 1.069 kHz (as measured with an oscilloscope).
I can change the duty from 0 to 100% and it works fine!
The problem is when I change the frequency: there is no effect on frequency when I change the period parameter of function setup_timer2. For example:
| Code: | | setup_timer2(TMR_INTERNAL | TMR_DIV_BY_1, 0x3326); |
I expected to change the frequency to: (140 MHz / 2) * (1) / (13095) = 5.346 kHz. But, in fact, I continue having a frequency of 1.069 kHz, like if this modification doesn't take any effect (the modification in the period from 0xFFC0 to 0x3326 doesn't take any effect).
I think that the period parameter of setup_timer2 is not working and timer2 is running like if period always was 0xFFFF.
I tried to change a lot of parameters, but it's been impossible to change the frequency of this PWM...
I'm using the version 4.136 of PCH/PCD CCS compiler.
Could anybody help me, please?
Best Regards,
Alex |
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jeremiah
Joined: 20 Jul 2010
Posts: 1348
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| Posted: Thu Mar 21, 2013 1:39 pm |
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At a glance (since you didn't post any code that creates the issue), setting the new frequency like that won't work like you expect. Your duty setting is higher than your period setting. Another thing is that you are setting up the output compare to not have any sync events. Some modules won't update to changes until the next sync event. Mind you, I have never used your specific chip...just experience from other ones. Also note that just because the chip datasheet says a particular value is the default for a register, the compiler may choose a value of 0 for some fields if you don't explicit call them out in the setup function).
You should really take a look at the family manual for output compare (section 13). It isn't part of the main data sheet, but is downloadable from the chips page on the microchip website (in the documents section). There may be some other settings (or another configuration completely) you need to figure out if you are wanting to change things like frequency on the fly. Changing duty on the fly is much easier and only requires the set_pwm_duty() call (which changes OCxR). To change the frequency might require setting up a couple different registers (or the right parameters for setup_compare(). See the chip .h file for a list of those and compare to the datasheet). |
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affonso.industra
Joined: 31 Jan 2013
Posts: 6
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| Posted: Fri Mar 22, 2013 12:07 pm |
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The problem was fixed using:
| Code: | setup_compare(1, COMPARE_PWM_EDGE | COMPARE_TIMER2 | COMPARE_TRIG_SYNC_TIMER2);
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The CCS support asked me to add COMPARE_TRIG_SYNC_TIMER2 and it works fine!
Thanks. |
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