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Setup timer for PWM pin on dsPIC33EP64GS806 not working

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DB_LXP

Joined: 15 Feb 2021
Posts: 1

Setup timer for PWM pin on dsPIC33EP64GS806 not working

Posted: Mon Feb 15, 2021 11:43 am

Hi All,

I am trying to setup one of my PWM pins on a dsPIC33EP64GS806. I have followed the example code in "ex_pwm_pcd.c" to setup the timer and compare functions. When I set a value for the period, I am not getting the desired frequency. For example, when I set a period of 25000 which will give me 100Hz (OSC/2*8*25000) I am only getting 38Hz. I have tried this with different TMR_DIV_BY values: 1, 8 and 64, and I get the following frequencies respectively: 305Hz, 38Hz and 4.8Hz. This is very mind boggling to me because I have also tried using the #use pwm() function and that works! So I am inclined to say that it is not a hardware problem, but possibly a setup problem. I could really use some guidance in solving this issue. Any help would be greatly appreciated. Thanks!

Code:

#include <33EP64GS806.h>
#device ADC=10

#fuses NOPROTECT, NOWDT
#fuses PR_PLL
#fuses XT
#fuses ICSP2
#FUSES CKSNOFSM
#pin_select OC1 = PIN_C3
#use delay(clock=40M, crystal=10M)

void main() {
/* Timer 2 setup */
setup_timer2(TMR_INTERNAL | TMR_DIV_BY_8,25000);
setup_compare(1, COMPARE_PWM_EDGE | COMPARE_TIMER2);
/* End Timer 2 setup */

set_pwm_duty(1,20000);

}

Here is my list file as well:

Ttelmah

Joined: 11 Mar 2010
Posts: 19537

Posted: Tue Feb 16, 2021 3:52 am

Two things wrong with what you post:

Code:

#include <33EP64GS806.h>
#device ADC=10
#device ICD=2 //Correct syntax to select the ICSP2 port.

#fuses NOPROTECT, NOWDT
#fuses PR_PLL
#fuses XT
//#fuses ICSP2 //not supported on your compiler
#FUSES CKSNOFSM
#pin_select OC1 = PIN_C3
#use delay(clock=40M, crystal=10M)

void main() {
/* Timer 2 setup */
setup_timer2(TMR_INTERNAL | TMR_DIV_BY_8,25000);
setup_compare(1, COMPARE_PWM_EDGE | COMPARE_TIMER2);
/* End Timer 2 setup */

set_pwm_duty(1,20000);
//You need to keep the chip awake otherwise the PWM won't happen...
while (TRUE)
delay_cycles(1);
}

Now what you posted, would not compile. The compiler would complain
about the ICSP setting, and with this fixed, as soon as it ran, it'd go
straight to sleep, so there would be no PWM output actually happening.

So, presumably what you were actually testing was not this code. Sad

This is doubly supported, since this code will not generate the listing you
actually show. This has a delay at the end preventing the sleep.

Not a good start....

Now, the time will not be quite what you expect, since the PR2 value is
'timebase-1', so it'll actually count to 25001. However it should give
very nearly the time you expect. Suggests to me, that in fact the CPU
is not running at the speed you think it is. When you say you tested with
the #USE PWM, double check that the fuse/clock settings you used for
this. Were the same as you are currently trying to use, and what frequency
you actually see. It actually looks as if the chip is running at about 14MHz,
not the 40MHz you are telling it you are running at.
Double check by doing a simple delay/loop code like:

Code:

#include <33EP64GS806.h>
#device ADC=10
#device ICD=2 //Correct syntax to select the ICSP2 port.

#fuses NOPROTECT, NOWDT
#fuses PR_PLL
#fuses XT
//#fuses ICSP2 //not supported on your compiler
#FUSES CKSNOFSM
#use delay(clock=40M, crystal=10M)

void main() {
//You need to keep the chip awake otherwise the PWM won't happen...
while (TRUE)
{
delay_ms(1);
output_toggle(PIN_C3);
}
}

If this does not generate a 500Hz output, you know that the problem is
the clock setup.

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