Arduino Timer Interrupt

I am actually working on a small project using an Arduino micro-controller ATMEGA 328. Timing issues are very critical so I had to find a way to use timer interrupts.

Arduino, Allegro 5804 and stepper motor
Arduino, Allegro 5804 and stepper motor

I found the following code and adapted it to the ATMEGA 328.

Following is my implementation for the ATMEGA 328 … The code is driving a stepper motor through the Allegro 5804 stepper motor driver.

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


#define CW     HIGH
#define CCW    LOW

// One and two phases
// 60000ms / 48steps = 1250ms/step
#define TRACK  1250

// Half steps
// 60000ms / 96steps = 625
//#define TRACK 625

int led13 = HIGH;
long counter = 0;
int stepStack = 0;

// Aruino runs at 16 Mhz, so we have 1000 Overflows per second...
// 1/ ((16000000 / 64) / 256) = 1 / 1000
ISR(TIMER2_OVF_vect) {
    // enqueue step message

void setup()
  pinMode(2, OUTPUT);  // Step
  pinMode(3, OUTPUT);  // Direction
  pinMode(13, OUTPUT); // LED

  pinMode(4, INPUT);   // Power on/off
  pinMode(5, INPUT);   // Rewind

  //Timer2 Settings: Timer Prescaler /64,
  TCCR2A |= (1<<CS22);
  TCCR2A &= ~((1<<CS21) | (1<<CS20));
  // Use normal mode
  TCCR2A &= ~((1<<WGM21) | (1<<WGM20));
  // Use internal clock - external clock not used in Arduino
  ASSR |= (0<<AS2);
  //Timer2 Overflow Interrupt Enable
  TIMSK2 |= (1<<TOIE2) | (0<<OCIE2A);

void loop()
  int fast = digitalRead(4);
  int rewind = digitalRead(5);

  if(rewind == HIGH || fast == HIGH)
    // Toggle the LED
    led13 ^= 1;
    digitalWrite(13, led13);

    // Clear the step messages buffer
    stepStack = 0;

    // Set rewind direction
    if(rewind == HIGH)
      digitalWrite(3, CCW);
      digitalWrite(3, CW);

    digitalWrite(2, HIGH);

    digitalWrite(2, LOW);
  else if(stepStack)
    // Toggle the LED
    led13 ^= 1;
    digitalWrite(13, led13); 

    // Set tracking direction
    digitalWrite(3, CW);

    digitalWrite(2, HIGH);

    digitalWrite(2, LOW);



  1. I’m trying to use this driver with a PF35T-48L4 (a unipolar stepper). Everything is wired up according to the research I’ve read (ignore center taps) and I’ve tried different wiring combinations, but can’t get the stepper to move. I had this stepper running on a unipolar driver before — I also tried connecting the center taps to +VDC but no luck.

    I checked all the stepper leads and the stepper driver for proper grounding, and verified that the outputs were firing.

  2. Hi Dan,

    I wired my stepper following the instructions of the datasheet at the following address but I guess that’s what you did.

    I dont know your skills in electronic so I’ll assume you are as I am, a newbe. Make sure your uses zener diodes to protect the driver and that they are connected the right way. I lost a few 5804 because of that.

    You should also make sure the power comming in the driver to drive the motors on pins 2 and 7 is regulated. I also lost a few chips because of that. :)

    As you did, I had to connect the center taps to the +VDC to make it work. Do you get any rotation or feedback from the motor?

    Would be great to have a picture so I can help a bit more.


  3. @pchretien
    There was no rotation at all no matter in what sequence I tried wiring the four leads.

    When I was building my own unipolar circuit (four transistors) and had things wired in the wrong order, I would at least get some jitter from the stepper.

    I’ll try hooking the center taps up again. The only thing I can figure out is that I’m not providing enough power to the stepper — ~5.4VDC out. The weird thing is I’ve succesfully driven it with under 5V before… but using the unipolar driver.

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