Timer1 acting weird on Arduino UNO (ATMEGA328)

Question

I am trying to implement a simple timer1 example that I saw on YouTube: http://youtu.be/Tj6xGtwOlB4?t=22m7s . The example was in c++ for stand alone ATMEGA328 chip and I am trying to get it to work on the Arduino UNO. Here is my working code:

void setup() {
  //initialize port for LED
  DDRB =  0b11111111; //initialize port B as output (really only care about 5th bit)
  PORTB = 0b00000000; //set ouput values to zero
  TCCR1A = 0; //clear control register A (not sure that I need this)
  TCCR1B |= 1<<CS10; //no prescaler, turns on CS10 bit of TCCR1B
}

void loop() {
  if (TCNT1 >= 255){
    TCNT1 = 0; //resets timer to zero
    PORTB ^=1<<PINB5; //1<<PINB5 is same as 0b00100000, so this toggles bit five of port b which is pin 13 (red led) on Arduino
  } 
}

Everything is working, but TCNT1 will only count up to 255. If I set the value in the if-statement to anything higher, the code in the if statement is never executed. Timer1 should be a 16-bit timer, so it does not make sense why the count stops at 255. Is arduino doing something behind the scenes to mess this up? It seems to work just fine in the example on youtube (without arduino).

Answer 1

First of all.... Why do you set the registers? Arduino's only benefit is that it wraps up some functions, so why not use it? Instead of

DDRB =  0b11111111;
PORTB = 0b00000000;
...
PORTB ^=1<<PINB5;

use simply

int myoutpin = XXXX; // Put here the number of the ARDUINO pin you want to use as output
...
pinMode(myoutpin, OUTPUT);
...
digitalWrite(myoutpin, !digitalRead(myoutpin));

I think that probably there are some similar functions for the timer too..

As for your question, I tried this code:

// the setup routine runs once when you press reset:
void setup() {
  TCCR1A = 0; //clear control register A (not sure that I need this)
  TCCR1B |= 1<<CS10; //no prescaler, turns on CS10 bit of TCCR1B
  Serial.begin(9600);
}

// the loop routine runs over and over again forever:
void loop() {
  if (TCNT1 >= 12000){
    TCNT1 = 0; //resets timer to zero
    Serial.println("Timer hit");
  } 
}

in a simulator and it works well; I should try it with a real Arduino, but I haven't any at the moment... As soon as i get one I'll try to use it

Answer 2

I've encountered the same problem, in the Atmel documentation, I found that other pins influence the counter mode. That is, the pins: WGM13,WGM12,WGM11,WGM10 are 0,1,0,0 respectively, the counter will be in CTC mode, meaning that it will count up to the value of OCR1A instead of (2^16-1) which might be the case in your code.

WGM11,WGM10 are bits 1,0 in TCCR1A and WGM13,WGM12 are bits 4,3 in TCCR1B so setting them to zero should do the job.

Answer 3

I had some thing like this with one of my code. I could not able to find the exact reason for the issue. At last I remove both setup and loop function an replace those with c code. Then it work fine. If you need those function then start code by clear both TCCR1A and TCCR1B register. I hope this is happened due to Arduino IDE not sure. But it works.