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4 square wave generation using PIC18F4520

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vinayakdabholkar

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Hello
I been have been reading the PIC18F4520 datasheet regarding the CCP section. For some reason i cant seem to understand how to start generation of PWM. I am highly confused.
I want to generate 4 square waves of same frequency and phase shifted by 90 to drive MOSFETS in a synchronous buck converter. The PWMs must be at 500K.
So to get the fatest operation from the MCU at what frequency must it be operated ? 20M looks optimimum or 40M ?
some one please guide me in this regard

- - - Updated - - -

I am using MIKRO C PRO
 

The PWM period =(PR2 +1) * 4 *Tosc *(TMR2 Prescale value)
On what basis to select this Prescale value ?
I want to generate a PWM at 500K with Fosc at 20M
 

What is the max pwm frequency that a PIC18F4520 can generate ?
 

so far i have realised it is not possible to generate 4 pwm signals from the CCP of PIC18F4520
So i am trying using timers. I have started with a basic code
Code: 
//Language: C
//Compiler: mikroC v8.20
//Programmer: vinayak

void main (void){
     TRISC = 0;
     PORTC = 0;
     INTCON=0xA4; //GIE=1;TMR0IE=1;TMR0IF=1
     T0CON=0xC0; //Prescalar of 1:2
     while(1)
     {
     if(INTCON.TMR0IF==1)
     {
     LATC.RC0=1;

     }
     }
}

Please guide me here to generate a 500Khz PWM signal. The PIC is running at 20Mhz
 

What is the best way to implement four 500K phase shifted square waves in PIC18F4520 CCP PWM ? or SW PWM using timer ?
 

will this code generate an interrupt after 2us ?
Code: 
//Program to generate 500Khz PWM using TIMER0
//Microcontroller: Microchip PIC184520
//Language: C
//Compiler: mikroC v8.20
//Programmer: vinayak

void main (void){
     TRISC = 0;
     PORTC = 0;
     INTCON=0b00100100; //GIE=0;TMR0IE=1;TMR0IF=1
     T0CON=0b11001000; //Prescalar of 1:1
     while(1)
     {
     void interrupt();

     }



}

void interrupt (void) {

                        if (INTCON & (1<<INTCON.TMR0IF))  // T0 overflowed ?
                        {
                        INTCON &= ~(1<<INTCON.TMR0IF);    // clear timer0 overflow bit.
                        }
                        // Fosc/4 x (Prescale) x (count to overflow) = repeat rate.
                        TMR0L = 0xF6;
                        TMR0L++; // Count 1us period
                        
                       }

- - - Updated - - -

I edited the code
PLease help me here
Code: 
//Program to generate 500Khz PWM using TIMER0
//Microcontroller: Microchip PIC184520
//Language: C
//Compiler: mikroC v8.20
//Programmer: vinayak

void main (void){

     TRISC = 0;
     PORTC = 0;
     TRISC.RC0=0;
     INTCON=0b00100100; //GIE=0;TMR0IE=1;TMR0IF=1
     T0CON=0b11001000; //Prescalar of 1:1
     while(1)
     {
     void interrupt();

     }



}

void interrupt (void) {
int i;

                        if (INTCON & (1<<INTCON.TMR0IF))  // T0 overflowed ?
                        {
                        INTCON &= ~(1<<INTCON.TMR0IF); // clear timer0 overflow bit.
                        TRISC.RC0=1;
                        }
                        // Fosc/4 x (Prescale) x (count to overflow) = repeat rate.
                        TMR0L = 0xF6;
                        for(i=0;i<256-TMR0L;i++)
                        {
                        TMR0L++; // Count 1us period
                        }
                        
                       }
 

i again tweeked the code and got the interrupt working but i get a error in proteus saying stack overflow is causing MCU to reset
What should i do here ?
Code: 
//Program to generate 500Khz PWM using TIMER0
//Microcontroller: Microchip PIC184520
//Language: C
//Compiler: mikroC v8.20
//Programmer: vinayak

void main (void){

     TRISC = 0;
     PORTC = 0;
     LATC.RC0=1;
     INTCON=0b10100100; //GIE=0;TMR0IE=1;TMR0IF=1
     T0CON=0b11001000; //Prescalar of 1:1
     //TMR0L = 0xFF+1;
     while(1)
     {
              int i;
                        if (INTCON & (1<<INTCON.TMR0IF))  // T0 overflowed ?
                        {
                        INTCON &= ~(1<<INTCON.TMR0IF); // clear timer0 overflow bit.
                        LATC.RC0=0;
                        }
                        TMR0L=0xF6;
                        for(i=0;i<255-TMR0L;i++)
                        {
                        TMR0L++;
                        }

     }


}
 

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By the looks of this thread you will struggle forever and never get it right.
My advice would be to go to the mikro web site and have a look at their online book.
If I remember rightly they have an example online that may also help you.
As you are using mikro C you might also find it helpful to type PWM into the code window and press F1
There is very comprehensive PWM library and help built in.
 
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