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tesla80
Joined: 23 May 2007
Posts: 81
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| 18F4520 PWM2 problem |
 Posted: Sat May 29, 2010 10:09 am |
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Hi all,
I'm generating a pulse for a transformer with 16F628 using the code below
| Code: | for(;;){
output_low(LED);
delay_us(25);
output_high(LED);
delay_us(30);
} |
So, I wanna do the same thing using 18F4520's PWM pin.
I'm using as PWM the CCP2 out of 18F4520.
And the code is here:
| Code: | #separate
void SwitchingStart(void)
{
long duty = 552;
output_low(PIN_C1);
setup_ccp2(CCP_PWM);
setup_timer_2(T2_DIV_BY_4,109,1); // 18181 Hz
set_pwm2_duty(duty); // 54%
}
#separate
void SwitchingStop(void)
{
setup_ccp2(CCP_OFF);
output_low(PIN_C1); // ccp2
setup_timer_2(T2_DISABLED,0,1);
} |
The ccp2 pin is connected through a 1k resistor to an NPN transistor's base.
But maybe I could not calculate the timer parameters and on the out of the transformer there are not any voltage. It worked with 16f628-code.
Where am I wrong? |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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tesla80
Joined: 23 May 2007
Posts: 81
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| Posted: Sat May 29, 2010 5:33 pm |
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The simple program works without problem. But when I change the timer and duty values, it does not work.
Working code:
| Code: | #include <18F4520.h>
#device *=16
#device adc=10
#FUSES WDT128 //Watch Dog Timer uses 1:128 Postscale
#FUSES INTRC_IO //Internal RC Osc, no CLKOUT
#FUSES PROTECT //Code protected from reads
#FUSES BROWNOUT //Reset when brownout detected
#FUSES BORV27 //Brownout reset at 2.7V
#FUSES PUT //No Power Up Timer
#FUSES CPD //Data EEPROM Code Protected
#FUSES STVREN //Stack full/underflow will cause reset
#FUSES NODEBUG //No Debug mode for ICD
#FUSES NOLVP //No Low Voltage Programming on B3(PIC16) or B5(PIC18)
#FUSES NOWRT //Program memory not write protected
#FUSES NOWRTD //Data EEPROM not write protected
#FUSES NOIESO //Internal External Switch Over mode enabled
#FUSES NOFCMEN //Fail-safe clock monitor enabled
#FUSES NOPBADEN //PORTB pins are configured as analog input channels on RESET
#FUSES NOWRTC //configuration not registers write protected
#FUSES NOWRTB //Boot block not write protected
#FUSES EBTR //Memory protected from table reads
#FUSES EBTRB //Boot block protected from table reads
#FUSES CPB //Boot Block Code Protected
#FUSES LPT1OSC //Timer1 configured for low-power operation
#FUSES NOMCLR //Master Clear pin disabled
#FUSES NOXINST //Extended set extension and Indexed Addressing mode disabled (Legacy mode)
#use delay(clock=32M,restart_wdt) // 4 x 8Mhz
void main(void)
{
setup_ccp2(CCP_PWM);
setup_timer_2(T2_DIV_BY_1, 255, 1);
set_pwm2_duty(128);
while(1){restart_wdt();}
}
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values calculated by pic wizard:
| Code: | setup_ccp2(CCP_PWM);
setup_timer_2(T2_DIV_BY_4, 109, 1);
set_pwm2_duty(552); |
The program does not work with these values above.
Last edited by tesla80 on Sat May 29, 2010 5:38 pm; edited 1 time in total |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sat May 29, 2010 5:38 pm |
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| Post the PWM frequency and duty cycle (in percent) that you want. |
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tesla80
Joined: 23 May 2007
Posts: 81
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| Posted: Sat May 29, 2010 5:41 pm |
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I want to generate the same signal which the code below generates
| Code: | for(;;){
output_low(LED);
delay_us(25);
output_high(LED);
delay_us(30);
} |
I think it is 18181 Hz 54% |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sat May 29, 2010 5:52 pm |
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| Quote: | setup_timer_2(T2_DIV_BY_4, 109, 1);
set_pwm2_duty(55L);
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I think if you change the duty cycle value to 55L, it might work better. |
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tesla80
Joined: 23 May 2007
Posts: 81
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| Posted: Sat May 29, 2010 6:04 pm |
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Thanks, I can't see the same voltage on seconder of the transformer but there is change.
What means the L ? |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sat May 29, 2010 7:04 pm |
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It puts it in 10-bit PWM mode (instead of 8-bit).
Actually 55L isn't correct for your desired duty cycle of 54%.
I should have said to use 238L for 10-bit mode or use 59 for 8-bit mode.
Example:
| Code: |
setup_pwm2_duty(59); // 8-bit PWM mode
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or
| Code: |
setup_pwm2_duty(238L); // 10-bit PWM mode
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Douglas Kennedy
Joined: 07 Sep 2003
Posts: 755
Location: Florida
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| Posted: Sun May 30, 2010 2:56 am |
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This is what I learned
Thanks PCM programmer
| Code: | set_timer2(0);
//// the timer2 post scaler is not used for PWM
/// Ex PIR2=9 osc=8mhz t2_div_by_1 freq=200khz
/// value = Fosc / (Fpwm * 4 * T2DIV) - 1 basically clock/4/(Fpwm*t2 divisor)-1
/// where value and T2DIV go into setup_timer_2(T2_DIV_BY_X, value aka PIR2, 1);
/// now to get the resolution high we want PIR2 at about 255
//// this isn't always possible depending on the clock aka Fosc so resolution is often lost
//// even when the pre scaler is the the miniumum of t2_Div_by_ 1
/// Ex t2DIV =1 Tosc 8mhz Fpwm=200khz PIR2+1=10 basically for 50% use 5 (8 bit) or 20L (10 bit)
/// value = Desired_Duty_Cycle% * (PIR2+1) 8bit or Desired_Duty_Cycle% * (PIR2+1)*4 10bit
/// set_pwm1_duty(value);
/// Duty cycle is 8bits or 10 bits depending if an int8 or int16 is passed
/// Ex setup_timer_2 ( T2_DIV_BY_1, 9, 1); for fpwm of 200khz at 8mhz
/// for 50% duty use set_pwm1_duty(5) 8bit or set_pwm1_duty(20L) 10bit
///
setup_timer_2 ( T2_DIV_BY_1, 9, 1);
setup_ccp1(CCP_PWM);///// setup PWM to be on CCP1
//set_pwm1_duty(5); ////// Ex 50% is 5/(9+1)
set_pwm1_duty(20L); ////// Ex 50% is 20/(4*(9+1)) |
The actual precision is not the full 8 bits or 10 bits due to the loss of precision in setting PIR2 |
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tesla80
Joined: 23 May 2007
Posts: 81
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| Posted: Sun May 30, 2010 3:12 pm |
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| PCM programmer wrote: | Example:
| Code: |
setup_pwm2_duty(59); // 8-bit PWM mode
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or
| Code: |
setup_pwm2_duty(238L); // 10-bit PWM mode |
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Hi, thanks,
There are difference between 10-bit variant and the 8-bit one.
10-bit variant generates 26us "1" and 20us "0".
8-bit variant generates 30us "1" and 25us "0".
In 10-bit variant the transistor heats up.
In 8-bit , everything is what I want.
Best regards |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun May 30, 2010 3:38 pm |
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When I wrote that answer, I wasn't at my office and I was tired from
working in the sun all afternoon. Sorry if it wasn't an exact answer.
I won't do that again. |
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tesla80
Joined: 23 May 2007
Posts: 81
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| Posted: Sun May 30, 2010 3:53 pm |
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Actually, It was exact answer.
Thanks again for your help. |
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