Timer set up problem

Projects Programming
1

Hello, everybody!

I am trying to set up the timer2 on my arduino, and flip a pin in the interrupt service routine, but what i am reading on the oscilloscope is not what i expect to (I would expect a square wave). I attach th reading to this post. Please could somebody help me to find my bug?

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

void setup() {
  pinMode(2, OUTPUT);

  // setup CTC
  TCCR2A &= ~(_BV(WGM20));
  TCCR2A |= _BV(WGM21);
  TCCR2B &= ~(_BV(WGM22)); 
  // set prescaler to 1
  TCCR2B &= ~(_BV(CS22) | _BV(CS21));
  TCCR2B |= _BV(CS20);
  // set output compare register
  OCR2A = 128;
  // enable the timer interrupt
  sei();
  TIMSK2 |= _BV(OCIE2A);
}

void loop() {
}

ISR(TIMER2_COMPA_vect) {
  PORTD ^= _BV(2); // flip pin 2 on port D
}

Thanks in advance.

scope_bw.jpg
scope_bw.jpg825×773 106 KB

2

That code works on my Arduino Uno R2. Maybe you have your scope setup wrong.

Also, you can simplify the setup code. (see below)

void setup() {
  pinMode(2, OUTPUT);

  // setup CTC
  TCCR2A = _BV(WGM21);
  // set prescaler to 1
  TCCR2B = _BV(CS20);
  // set output compare register
  OCR2A = 128;
  // enable the timer interrupt
  TIMSK2 = _BV(OCIE2A);
}