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memoally
Joined: 25 Jan 2010
Posts: 35
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| Why can't I generate pulses with pwm? help please |
 Posted: Thu Feb 04, 2010 4:38 pm |
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Hi everyone. I use 16f873. Our aim is to use pwm module of this pic for a project. But I can't generate pulses with this PIC although I can use pwm modules for other pics (e.g. 18f4620, 18f4431). I tried a simple network to generate pulse with via external interrupt but it failed. I request you to help me to find where the problem is or which part of code or network is wrong? Here is the code:
| Code: |
#include "C:\ccsc pic uygulamalar\kendi uygulamalarım\ uyg4_for_pwm.h"
int duty;
#int_EXT
void EXT_isr(void)
{
duty=duty+10;
set_pwm2_duty(duty);
}
void main()
{
setup_adc_ports(NO_ANALOGS);
setup_adc(ADC_OFF);
setup_spi(SPI_SS_DISABLED);
setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1);
setup_timer_1(T1_DISABLED);
setup_timer_2(T2_DIV_BY_16,255,1);
setup_ccp2(CCP_PWM);
set_pwm2_duty(10);
enable_interrupts(INT_EXT);
ext_int_edge(H_TO_L);
enable_interrupts(GLOBAL);
set_tris_c(0x00);
while(1);
}
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I also add the network to a image site.here it is:
http://img508.imageshack.us/img508/765/network.jpg
I also add the network while it is being animated.here it is:
http://img46.imageshack.us/img46/2213/animatingresult.jpg
I want to increase duty cycle via pressing button, but I got flat response as it is in the picture. This network works for other pics.
I don't know how to add source codes or proteus network files, so forgive me. If anyone knows where the problem is, please correct me.
_________________
compiler version: 4.105
pic: 16f876
clock frequency: 4MHz |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Feb 04, 2010 6:38 pm |
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Try a simple test program for pwm on CCP2. See if you get anything
on the oscilloscope.
| Code: |
#include <16F873.H>
#fuses XT, NOWDT, BROWNOUT, PUT, NOLVP
#use delay(clock=4000000)
//=====================================
void main(void)
{
setup_ccp2(CCP_PWM);
setup_timer_2(T2_DIV_BY_1, 255, 1);
set_pwm2_duty(128);
while(1);
}
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Rohit de Sa
Joined: 09 Nov 2007
Posts: 282
Location: India
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| Posted: Thu Feb 04, 2010 11:21 pm |
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PWM requires the use of timer resources. When dealing with timers always mention the clock speed. It helps in sorting out issues. The relevant equations are: | Code: | | (Tpwm)=4(Tosc)(Prescale)(PR2+1) |
or | Code: | | (Fpwm)=(Fosc)/(4.(Prescale)(PR2+1)) |
And, | Code: | (Ton)=(duty value)(Tosc)(Prescale)
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Depending on your clock speed, it is possible that the output is always high; ie, if Ton>Tpwm. I don't know what your clock speed is, so I can't troubleshoot.
Rohit |
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Rohit de Sa
Joined: 09 Nov 2007
Posts: 282
Location: India
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| Posted: Fri Feb 05, 2010 3:36 am |
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| I wrote: | | I don't know what your clock speed is, so I can't troubleshoot |
I was just doing a little bit of algebraic rearrangement and I realized that although knowing Fosc is important, if it's just a quick check that you want to make, you don't _need_ it, per se. Just make sure that | Code: | (Tpwm) > (Ton)
» 4(Tosc)(Prescale)(PR2+1) > (duty value)(Tosc)(Prescale)
» 4(PR2+1) > (duty value) |
Rohit |
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memoally
Joined: 25 Jan 2010
Posts: 35
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| Posted: Fri Feb 05, 2010 10:30 am |
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first of all thank you,pcm programmer;but it just did not work. i know your coding is true, i also know my codes were true but i can not get the right result  the interesting part is that i can get what i want with 18f pics, but i can not get it with various 16f pics,like 16f628a,16f877,16f870 and 16f872. even a simple led blinking problem is not working with 16f's where as there is no problem for 18f's :D i think it may come from program (?).
i use ccs picc PCWHD compiler. may the problem come from this?
rohit i also thank you, my clock speed was 4MHz, i tried various speeds but i can not get anything. i also tried external clock with crystal and capasitors,but i did not work again.
an interesting problem and i am about to go crazy :D
by the way,you should advise to use 18f pics :D but i am to program a 16f872 pic which the pcb is ready so i am limited with pin numbers and circuit schematic
_________________
compiler version: 4.105
pic: 16f876
clock frequency: 4MHz |
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Guest
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| Re: Why can't I generate pulses with pwm? help please |
| Posted: Fri Feb 05, 2010 10:41 am |
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| memoally wrote: | Hi everyone. I use 16f873. Our aim is to use pwm module of this pic for a project. But I can't generate pulses with this PIC although I can use pwm modules for other pics (e.g. 18f4620, 18f4431). I tried a simple network to generate pulse with via external interrupt but it failed. I request you to help me to find where the problem is or which part of code or network is wrong? Here is the code:
| Code: |
#include "C:\ccsc pic uygulamalar\kendi uygulamalarım\ uyg4_for_pwm.h"
int duty;
#int_EXT
void EXT_isr(void)
{
duty=duty+10;
set_pwm2_duty(duty);
}
void main()
{
setup_adc_ports(NO_ANALOGS);
setup_adc(ADC_OFF);
setup_spi(SPI_SS_DISABLED);
setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1);
setup_timer_1(T1_DISABLED);
setup_timer_2(T2_DIV_BY_16,255,1);
setup_ccp2(CCP_PWM);
set_pwm2_duty(10);
enable_interrupts(INT_EXT);
ext_int_edge(H_TO_L);
enable_interrupts(GLOBAL);
set_tris_c(0x00);
while(1);
}
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This code has no fuse and clock speed settings. How can it work? Why don't you try a simple program WITH the #fuse and clock settings and just try using a simple delay statement to turn a pin on high and low at a 1 second interval. You can check it on the scope. |
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memoally
Joined: 25 Jan 2010
Posts: 35
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| Posted: Fri Feb 05, 2010 11:09 am |
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Where do you know there is no fuse options? There is a header file you see? I can set them in the program menu, and it creates which fuses will be used or not, here it is:
| Code: |
#include <16F873.h>
#device adc=8
#FUSES NOWDT //No Watch Dog Timer
#FUSES RC //Resistor/Capacitor Osc with CLKOUT
#FUSES NOPUT //No Power Up Timer
#FUSES PROTECT //Code protected from reads
#FUSES NOBROWNOUT //No brownout reset
#FUSES NOLVP //No low voltage prgming, B3(PIC16) or B5(PIC18) used for I/O
#FUSES NOCPD //No EE protection
#FUSES NOWRT //Program memory not write protected
#FUSES NODEBUG //No Debug mode for ICD
#use delay(clock=4000000) |
_________________
compiler version: 4.105
pic: 16f876
clock frequency: 4MHz |
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Guest
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| Posted: Fri Feb 05, 2010 12:37 pm |
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| Okay, did you try to turn a single pin high and low using a simple delayms function to do a simple test first? |
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memoally
Joined: 25 Jan 2010
Posts: 35
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| Posted: Fri Feb 05, 2010 1:05 pm |
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yes it is also not working... :(((( there is a problem with 16f's :(((
_________________
compiler version: 4.105
pic: 16f876
clock frequency: 4MHz |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Feb 05, 2010 1:32 pm |
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| Quote: | #include <16F873.h>
#device adc=8
#FUSES NOWDT //No Watch Dog Timer
#FUSES RC //Resistor/Capacitor Osc with CLKOUT |
Why are you doing this ? Are you really using the external resistor
and capacitor oscillator ? If so, what are the values ? |
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memoally
Joined: 25 Jan 2010
Posts: 35
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| Posted: Fri Feb 05, 2010 1:37 pm |
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When I use crystal, I set fuses as XT. I tried a 8MHz crystal and two 22pF capacitors into ocs1/clkin and osc2/clkout pins. I also tried 4,2,1 Mhz crystals...
_________________
compiler version: 4.105
pic: 16f876
clock frequency: 4MHz |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Feb 05, 2010 1:44 pm |
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Is this project being done on a real hardware board, is it all just a
Proteus project ? |
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memoally
Joined: 25 Jan 2010
Posts: 35
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| Posted: Fri Feb 05, 2010 1:51 pm |
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i also tried it on real hardware,again disappointment :(
_________________
compiler version: 4.105
pic: 16f876
clock frequency: 4MHz |
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memoally
Joined: 25 Jan 2010
Posts: 35
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| Posted: Fri Feb 05, 2010 1:52 pm |
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maybe i should rework on timers but i dont think that the resource of the problem is from timer. (?)...
_________________
compiler version: 4.105
pic: 16f876
clock frequency: 4MHz |
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Rohit de Sa
Joined: 09 Nov 2007
Posts: 282
Location: India
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| Posted: Fri Feb 05, 2010 7:38 pm |
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Leave timers and PWM aside for the moment. Try getting an LED to flash first. A flashing LED is to microcontroller programming what "hello world" is to coding on a PC.
Rohit |
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