Search code examples
timerembeddedsystemavratmega32

Output Compare match doesn't happen - AVR Atmega32

I'm trying to count my clicks on a push button (Coun and simulates it on 4 leds it must count till 9 , then TCNT0 equals OCR0 , so Interrupt is fired and TCNT0 becomes zero again and so on . but it continues after 9 till 255 . output compare match flag isn't set . (no compare match happens).

ISR(TIMER0_COMP_vect){

}

int main(){
    DDRC=0xff;          //configure PORTC leds
    CLEAR_BIT(DDRB,0);   //configure T0 Pin as input
    SET_BIT(PORTB,0);    //enable internal PULL-UP resistance
    TCCR0 = 0x4E;     //Counter mode(falling edge),CTC mode .
    TCNT0=0;        //timer register initial value
    OCR0=9;       //set MAX value as 9
    SET_BIT(TIMSK,OCIE0);  //Enable On compare interrupt

    SET_BIT(SREG,7);      //Enable All-interrupts
    while (1){
        PORTC=TCNT0;           //Let Leds simulates the value of TCNT0
                    }
    }
Solution

  • Better avoid "magic numbers":

    TCCR0 = 0x4E;     //Counter mode(falling edge),CTC mode .

    To set CTC bit #6 WGM00 should be 0, while bit #3 WGMM01 should be 1 (Refer to the datasheet, table 38 at page 80).

    You have both bits set to 1, thus the counter is working in FastPWM mode.

    Use macros with bit names:

    TCCR0 = (1 << WGM01) | (1 << CS02) | (1 << CS01); // = 0x0E