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software PWM,

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greenears
Guest

software PWM,

Posted: Mon May 22, 2006 1:44 pm

HI

I'm pretty new to PIC programming and I'm trying to program software pwm (see code)

Code:

//-----
//interrupt routines
//----

unsigned int16 pwm_duty_cycle;
unsigned int1 bit_state=0;

#int_timer3 //
void timer3_isr() {
switch(bit_state) {
case 1:
OUTPUT_FLOAT(PIN_BIRD1B);
bit_state=0;
set_timer3(0xFFFF-pwm_duty_cycle); // pwm_duty_cycle
break;
case 0:
OUTPUT_LOW(PIN_BIRD1B);
bit_state=1;
set_timer3(0xFFFF-(50-pwm_duty_cycle)); // period-pwm_duty_cycle
break;
}

}

//---------------------------------------------------------------------------------------------------------------
// Initialization
//---------------------------------------------------------------------------------------------------------------

void init()
{

// Setup oscillator mode @ 32MHz
// setup_oscillator(OSC_8MHZ|OSC_NORMAL|OSC_31250|OSC_PLL_ON);
#asm
MOVLW 0b01110000 // setup internal oscillator
MOVWF 0xFD3
MOVLW 0b11000000 // enable PLL
MOVWF 0xF9B
#endasm

// Setup peripherals
setup_adc_ports(AN0_TO_AN4);
setup_adc(ADC_CLOCK_DIV_32);       // ADC clock must be set such to ensure TAD=1.6us minimum (TOSC = 0.05us @ 20MHz)

setup_psp(PSP_DISABLED);
setup_spi(FALSE);
setup_wdt(WDT_OFF);

setup_timer_0(RTCC_INTERNAL|RTCC_DIV_32); //
setup_timer_1(T1_INTERNAL|T1_DIV_BY_8); /
setup_timer_2(T2_DIV_BY_16,255,1);
setup_timer_3(T3_INTERNAL|T3_DIV_BY_8);
setup_ccp1(CCP_PWM);
setup_ccp2(CCP_PWM);

//setup_comparator(NC_NC_NC_NC);
//setup_vref(FALSE);
setup_low_volt_detect(FALSE);

// Setup PIC I/O ports; 1 indicates the pin is input and 0 output.
set_tris_a(0b00011110);
set_tris_b(0b11110011);
set_tris_c(0b10000000);
set_tris_d(0b11111111);
set_tris_e(0b100);

delay_ms(100);

// Setup interrupts.
enable_interrupts(INT_TIMER1); // Anemometer monitoring
enable_interrupts(INT_TIMER3); // BIRDS PWM
enable_interrupts(global);

}

//---------------------------------------------------------------------------------------------------------------
// MAIN routine
//---------------------------------------------------------------------------------------------------------------

void main() {
init();
//while (true) {
led_on_led0();

pwm_duty_cycle=20; // trying to set the duty cycle to control actuators

led_off_led0();

}

It is a PIC18F4620 @32MHz, TImer3 is 16bit
so after my calculation
it overflows every 65.5ms
(4/32E6 * 65535 *8=65.5ms)

and if I want a frequency of 20kHz (50us period) of my PWM
.....(4/32E6 * x *8=50us) => x=50 counts in timer3

my problem is that I can not change the fraction of high to low states of the pwm...
Are my calculations correct? Is it very unelegant to do PWM this way/are there mistakes?
Did I enable the Interrupts correctly...?

I'm stuck on this topic for quite a while now...
Thank you very much!
(Youre saving my life)

best

mirko

Rolling Eyes

PCM programmer

Joined: 06 Sep 2003
Posts: 21708


Posted: Mon May 22, 2006 1:57 pm

http://www.ccsinfo.com/forum/viewtopic.php?t=20050

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