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16F877A dual PWM signals problem

 
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desert
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16F877A dual PWM signals problem
PostPosted: Fri Nov 28, 2008 10:12 am     Reply with quote
hi all,

I try to generate 2 PWM signals at CCP1 & CCP2 via this simple code:
Code:

#include <16F877.h>
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock = 4000000)

void main()
{
output_low(PIN_C1);   // Set CCP2 output low
output_low(PIN_C2);   // Set CCP1 output low

setup_ccp1(CCP_PWM);  // Configure CCP1 as a PWM
setup_ccp2(CCP_PWM);  // Configure CCP2 as a PWM

setup_timer_2(T2_DIV_BY_4, 124, 1);  // 500 Hz     
set_pwm1_duty(62);                    // 25% duty cycle on pin C2
set_pwm2_duty(62);                    // 50% duty cycle on pin C1

while(1);  // Prevent PIC from going to sleep  (Important !)
}

Checking with a scope I get the PWM I want at CCP2 but no luck on CCP1 no matter what I do.
Could this be due to a faulty PIC?
Is there a way to rule out this option?

Thanks for the help,
Moshe
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Fri Nov 28, 2008 11:47 am     Reply with quote
Are there any external components connected to the CCP1 pin (Pin C2) ?
desert
Guest
PostPosted: Fri Nov 28, 2008 3:36 pm     Reply with quote
No, I disconnected everything so I can examine the micro controller alone.
it was originally connected to an H BRIDGE, but once it failed I started investigating.
the whole thing is mounted on a breadboard, but I sample the signal at the chip leg directly.
I find the chances of a hardware malfunction slim, but who knows...
any guesses or suggestions will be welcome.

thanks,
Moshe.
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Fri Nov 28, 2008 3:49 pm     Reply with quote
Quote:
it was originally connected to an H BRIDGE, but once it failed

Try a new PIC.
desert
Guest
PostPosted: Fri Nov 28, 2008 4:10 pm     Reply with quote
thanks for the help, I will try...
mlkushan



Joined: 16 Nov 2008
Posts: 22
Location: Sri Lanka

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Sample code to generate two 40KHz PWM signals
PostPosted: Tue Dec 02, 2008 12:20 am     Reply with quote
Hi,

Check this code segment. This works fine. Hope this will be helpful to you also. This generates 40KHz PWM signals on both PIN_C1 and PIN_C2.

Thanks.

Code:

#include <16F877A.h>
#device adc=8

#FUSES NOWDT                    //No Watch Dog Timer
#FUSES XT                       //Crystal osc <= 4mhz
#FUSES NOPUT                    //No Power Up Timer
#FUSES NOPROTECT                //Code not protected from reading
#FUSES NODEBUG                  //No Debug mode for ICD
#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 WRT_50%                  //Lower half of Program Memory is Write Protected

#use delay(clock=4000000)
#use rs232(baud=9600,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8)

void main()
{
   int16 pwm_duty = 50;              //to get  a higher resolution
   
   setup_adc_ports(NO_ANALOGS);
   setup_adc(ADC_OFF);
   setup_psp(PSP_DISABLED);
   setup_spi(SPI_SS_DISABLED);
   setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1);
   setup_timer_1(T1_DISABLED);
   setup_timer_2(T2_DIV_BY_1,24,1);
   setup_ccp1(CCP_PWM);
   setup_ccp2(CCP_PWM);
   set_pwm1_duty(pwm_duty);
   set_pwm2_duty(pwm_duty);
   setup_comparator(NC_NC_NC_NC);
   setup_vref(FALSE);

   // TODO: USER CODE!!
   while(1);

}

_________________
Kushan Sharma
mlkushan@gmail.com
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