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updated code as answered

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edited May 30, 2020 at 5:32

Update working code

int var;
void setup() {
  // put your setup code here, to run once:
  SREG = SREG | (1<<7);          // Gloval interrupt enable
  TCCR0A =(1<<WGM01); // Clear counter on compare match mode
  OCR0A = 255; // when TCNT equal OCR0 interrupt will generate
  TIMSK0 = (1<<OCIE0A); //  Output Compare Match A Interrupt Enable
  TCCR0B = (1<<CS00) | (1<<CS02);  // Prescaling by 1024


  DDRB = DDRB | (1<<5); 

    Serial.begin(9600);      // Initialize the USART  
    Serial.println("Start");   // Write the welcome message

}

void loop() {
  // put your main code here, to run repeatedly:

}

ISR(TIMER0_COMPA_vect){
  var++;
 // Serial.print(var);
  volatile long unsigned i;
  if(var == 246){
        PORTB = PORTB | (1<<5);
        for(i=0; i<300000; i++);
        PORTB = PORTB & ~(1<<5);
        var=0; 
  }
}

Update working code

int var;
void setup() {
  // put your setup code here, to run once:
  SREG = SREG | (1<<7);          // Gloval interrupt enable
  TCCR0A =(1<<WGM01); // Clear counter on compare match mode
  OCR0A = 255; // when TCNT equal OCR0 interrupt will generate
  TIMSK0 = (1<<OCIE0A); //  Output Compare Match A Interrupt Enable
  TCCR0B = (1<<CS00) | (1<<CS02);  // Prescaling by 1024


  DDRB = DDRB | (1<<5); 

    Serial.begin(9600);      // Initialize the USART  
    Serial.println("Start");   // Write the welcome message

}

void loop() {
  // put your main code here, to run repeatedly:

}

ISR(TIMER0_COMPA_vect){
  var++;
 // Serial.print(var);
  volatile long unsigned i;
  if(var == 246){
        PORTB = PORTB | (1<<5);
        for(i=0; i<300000; i++);
        PORTB = PORTB & ~(1<<5);
        var=0; 
  }
}

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asked May 29, 2020 at 17:02

user143252

Arduino Uno CTC mode interrupt is not tiggering

I am trying to generate LED blink after 4 second using Interrupt but Interrupt is not triggering not even once . Request: if you have arduino uno r3 please check at your end and let me know result. I have read Timer counter section multiple times and applied everything i can for example :-

Enabled Global Interrupt
Select CTC Mode
Enable Interrupt for OCIE0A
Prescaling to clk/1024
Initializing OCR0A
When OCR0A equal TCNT0 ,interrupt will generate

int var;
void setup() {
  // put your setup code here, to run once:
    SREG = SREG | (1<<7);          // Gloval interrupt enable
    TCCR0A = TCCR0A | (1<<WGM01); // Clear counter on compare match mode
    OCR0A = 255; // when TCNT equal OCR0 interrupt will generate
    TIMSK0 = TIMSK0 | (1<<OCIE0A); //  Output Compare Match A Interrupt Enable
    TCCR0B = TCCR0B | (1<<CS01) | (1<<CS02);  // Prescaling by 1024
    DDRB = DDRB | (1<<5); 
    Serial.begin(9600);      // Testing 
    Serial.println("Start");   // Testing
}

void loop() {
  // put your main code here, to run repeatedly:

}

ISR(TIMER0_COMPA_vect){
    var++;
    Serial.print(var); // Testing
    volatile long unsigned i;
    if(var == 246){
        PORTB = PORTB | (1<<5);
        for(i=0; i<30000; i++);
        PORTB = PORTB & ~(1<<5);
        for(i=0; i<30000; i++);
        var=0; 
    }
}

clock is 16 00 00 00 Hz
Prescaling by 1024 = 15625
1 Tick = 1/15625 = 0.00 00 64 sec
OCR0 is initialized by 255
TCNT0 Ticks to 255
Total time taken to generate one interrupt = 255 * 0.00 00 64 = 0.01632 sec that means after every 0.01632 sec Interrupt supposed to generate
How many interrupt is required to generate LED after 4 sec => 4/0.01632 = 246