AVRFreaks.net

#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/sleep.h>

enum { UP, DOWN };


int main (void)
{

    /* Timer 1 is 10-bit PWM (8-bit PWM on some ATtinys).
      Setting WGM10 & WGM11 only will give phase correct PWM
      Setting WGM12 also will give fast PWM, but that's on TCCR1B
      COM1A1 = Clear OC1A on match when upcounting-Set OC1A
               when downcounting on match
   */
    TCCR1A |= ((1<<WGM10)|(1<<WGM11)|(1<<COM1A1));
   /* Clock Selects are for prescallers
      Current CS10 is for clock without prescalling
      Prescaler    8 = (1<<CS11)
      Prescaler   64 = ((1<<CS11)|(1<<CS10))
      Prescaler  256 = (1<<CS12)
      Prescaler 1024 = ((1<<CS12)|(1<<CS10))
   */
    TCCR1B |= ((1<<WGM12)|(1<<CS10));

    // Set Timer1/PWM register value to 0.
    OCR1A = 0;

    /* Enable OC1A or PB3 as output.
      Not sure why but only works with this pin
   */
    DDRB = (1<<3);

    // Enable timer1 overflow interrupt.
    TIMSK = (1<<TOIE1);

    sei ();

    // loop forever, the interrupts are doing the rest
    for (;;)                   
        sleep_mode();

    return (0);
}

ISR (TIMER1_OVF_vect)
{
    static uint16_t pwm;      //pwm counter var
    static uint8_t direction;   //enum var

   /*
   For those who are wondering by ++pwm, it's actually
      incrementing or decrementing everytime through the switch
      However, it does that before comparing to min or max
   */
    switch (direction)         
    {
        case UP:   //increment counter and check against Max-1
            if (++pwm == 1023)
            //start the counting other direction
                direction = DOWN;
            break;

        case DOWN:   //decrement counter and check against min
            if (--pwm == 0)
            //start counting in other direction
                direction = UP;
            break;
    }
   //set the calc'd value to Timer1 output register
    OCR1A = pwm;
}



/*
 * Obtained from http://www.nongnu.org/avr-libc/user-manual/group__demo__project.html
 * ----------------------------------------------------------------------------
 * "THE BEER-WARE LICENSE" (Revision 43):
 * <joerg@FreeBSD.ORG> wrote this file.  As long as you retain this notice you
 * can do whatever you want with this stuff. If we meet some day, and you think
 * this stuff is worth it, you can buy me a beer in return.        Joerg Wunsch
 * Hey I wanna beer too ;) Actually jack & coke or a smoke, but same deal: Bart Robinson
 * ----------------------------------------------------------------------------
 *
 * Simple AVR demonstration.  Controls a LED that can be directly
 * connected from OC1/OC1A to GND.  The brightness of the LED is
 * controlled with the PWM.  After each period of the PWM, the PWM
 * value is either incremented or decremented, that's all.
 *
 * $Id: group__demo__project.html,v 1.1.1.18 2009/03/05 20:35:12 joerg_wunsch Exp $
 */

// The following two ISRs are doing "poor man's PWM"
//  but this allows it to be on a pin of my choice
ISR(TIMER0_COMP_vect) {
        // clear the output pin on OCR0 match
   PORTC &= ~(1<<PC0);
}
ISR(TIMER0_OVF_vect) {
        // set the output pin at timer overflow
   PORTC |= (1<<PC0);
}

int main(void) {

   // going to use PORTC.0 to PWM the contrast voltage
   DDRC = (1<<DDC0);
   TIMSK |= ((1<<OCIE0) | (1<<TOIE0)); // use both interrupts
   OCR0 = 10; // 10 out of 256 means very short on period (low voltage)
   TCCR0 = (1<<CS00); // timer on - nice high PWM frequency

   // Might later consider PWMing the backlight voltage too
   // so it would also be adjustable ...
   sei();

duty = top * value / 1024;

DDRB   = (1 << 3 ) | ( 1 << 2) | (1 << 1);

TCCR1A |= (1 << COM1A1) | ( 1 << COM1B1 ) ; //set both to non inverting mode
TCCR1A |= (1 << WGM11);
TCCR1B |= (1 << WGM13) | (1 << WGM12) ;
ICR1 = 65535;

OCR1A = 60000;
OCR1B = 60000;

OCR1AH = 60000 >> 8;
OCR1AL = 60000;