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Bill Legge
Joined: 07 Sep 2010
Posts: 24
Location: West Australia
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| Hardware PWM problem using PCD |
 Posted: Fri Nov 26, 2010 9:20 pm |
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I've written a function to set one of the hardware PWM modules
to a desired frequency and pulse duration.
Uses a 8MHz Xtal so one cycle=0.25uS
And timer2 in 32_bit mode, the code is:
| Code: |
// MCU is PIC24FJ64GA010 using PCD/24_bit
#include <main.h>
/////////////////////////////////////////////////////////////////////////////
// function to set hardware PWM
// module must be set inside this function
// passed: fx frequency in [Hz]
// t_on time on as a percentage of period
// uses timer23 in 32_bit mode
// the PWM period will be (1/clock)*2*t2div*(period+1)
// clock=8MHz. Clock period=1/8MHz=0.125uS. Tcy=fosc/2=0.25uS
// period[uS]=0.25*overflow=1/frequency
// overflow=4000000/frequency
void hardware_PWM(int32 fx,int32 t_on)
{
// select HPWM module 1 to 5
const int8 module=2;
// convert fx to overflow in [Tcy]
int32 overflow=4000000/fx;
// convert percentage t_on to [Tcy]
t_on=overflow*t_on/100;
setup_timer2(TMR_INTERNAL | TMR_32_BIT, overflow);
setup_compare(module, COMPARE_PWM | COMPARE_TIMER2);
set_pwm_duty(module,t_on);
}
/////////////////////////////////////////////////////////////////////////////
void main()
{
setup_spi( FALSE );
setup_spi2( FALSE );
setup_wdt(WDT_OFF);
// globals
int32 frequency; // desired frequency in Hz
int32 time_on; // % pulse duration
time_on=10; // 10% time_on
while(TRUE)
{
for(frequency=1000;frequency<=10000;frequency=frequency+200)
{
hardware_PWM(frequency,time_on);
delay_ms(2000);
}
}
}
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The function works OK if I call it once.
But calling it in a 'slow loop' (2 seconds long so that the PWM settles and I get time to read the scope) produces the desired pulses for a few iterations - and then goes haywire???
Any ideas please?
Regards Bill Legge
_________________
Denmark in West Australia
'Where the forest meets the sea' |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Nov 28, 2010 2:13 pm |
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Debug it. Find out which input numbers cause the function to fail.
Put printf statements in your function. Display the results of your math.
The math may not work with certain numbers or a certain range.
Try testing it over a much smaller range than 1000 to 10000.
Also, you are doing things that are unconventional for CCS, such as this:
| Quote: | | int32 overflow=4000000/fx; |
It may work. It may not. If you have a problem with some code, it's a
good idea to "back off" on unconventional coding. Split that line up into
two lines, one for the declaration and another for the math.
Try stopping the PWM module completely before you re-program it.
In other words, question everything. Get down into the code and
experiment. |
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