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hubble
Joined: 11 Dec 2006
Posts: 10
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| !!! Help me with PWM !!! |
 Posted: Sat Sep 13, 2008 9:15 am |
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How can I get next graphs?
1. on CCP1 - PWM in odd period;
2. on CCP2 - PWM in even period.
Graphic and code below:
| Code: |
CCP1 _|''''|________________________|''''|______________
CCP2 _______________|''''|__________________________|''''|___
| | | |
| | | |
|<-1st period->|<-2nd period-> | <-3rd period->|
|
| Code: | #include <16F886.h>
#device ADC=10
#fuses HS,NOWDT,BROWNOUT,PUT,NOLVP
#use delay (clock=4000000)
#define PR2 49 // 20kHz
//!#byte PWM1CON = 0x9B
#byte CCP1CON = 0x17
#byte CCP2CON = 0x1D
int16 currentDuty;
//=================================
#int_timer2
void Interrupt_RTCC()
{
int8 changeCCP;
changeCCP^=1;
if(changeCCP)
set_pwm1_duty(currentDuty);
else
set_pwm2_duty(currentDuty);
}
//=================================
void main()
{
int16 oldDuty;
enable_interrupts(GLOBAL);
enable_interrupts(INT_TIMER2);
setup_port_a(ALL_ANALOG);
setup_adc(adc_clock_internal);
set_adc_channel(0);
set_tris_b(0xff);
set_tris_c(0xff);
CCP1CON=0b00101100;
CCP2CON=0b00101100;
//!PWM1CON=0b00000010;
setup_timer_2(T2_DIV_BY_1,PR2,1);
set_tris_b(0);
set_tris_c(0);
output_c(0);
while(1)
{
currentDuty=read_adc();
if (oldDuty!=currentDuty){
currentDuty=currentDuty*(PR2+1)/255;
//! set_pwm1_duty(currentDuty);
//! set_pwm2_duty(currentDuty);
oldDuty=currentDuty;
}
delay_ms(10);
}
} |
It works, but not what I wanted 
Help me with question.
Thank beforehand. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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Guest
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| Posted: Sat Sep 13, 2008 3:34 pm |
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Thank you PCM programmer.
It works.
But if I change the next variable
#define PWM_PERIOD 1000L
#define PULSE_ON_TIME 250L
to (for example)
#define PWM_PERIOD 1000L
#define PULSE_ON_TIME 50L
or to (for example too)
#define PWM_PERIOD 250L
#define PULSE_ON_TIME 150L
then I have bad (very bad) graphs on me oscilloscope.
What`s wrong?
Can you help me again? |
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RLScott
Joined: 10 Jul 2007
Posts: 465
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| Posted: Sat Sep 13, 2008 7:00 pm |
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| Anonymous wrote: | ...But if I change the next variable
#define PWM_PERIOD 1000L
#define PULSE_ON_TIME 250L
to (for example)
#define PWM_PERIOD 1000L
#define PULSE_ON_TIME 50L
|
50 is probably too short for the interrupt service routine.
| Quote: |
or to (for example too)
#define PWM_PERIOD 250L
#define PULSE_ON_TIME 150L
|
This leaves pulse_off_time equal to 100, which might also be too short for the interrupt service routine.
One way to speed up the interrupt service routine from the one posted in the referenced thread is to replace the setup_ccp1 and setup_ccp2 functions with a single bit setting or bit clearing instruction that does the same thing.
_________________
Robert Scott
Real-Time Specialties
Embedded Systems Consulting |
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