Controls a 4 phase 28BYJ-48 stepper motor, via some digital pins an an LM2003 driver

Stepper.ino

// Control a 4 phase stepper motor with an Arduino
// Controls a 28BYJ-48 stepper motor, via some digital pins an an LM2003 driver
// Uses direct port manipulation for fast concurrent pin state changes
// https://en.wikipedia.org/wiki/Stepper_motor#/media/File:Drive.png

int motorSpeed = 1000;
int count = 0;
int countsperrev = 32*16;

// can do > 1100 uS
int lookup[8] = {B1000,
                 B1000,
                 B0100,
                 B0110,
                 B0010,
                 B0011,
                 B0001,
                 B1001};

// can do > 800 uS
//                abcd
int wave[12] =  {B1000,
                 B1000,
                 B1000,
                 B0100,
                 B0100,
                 B0100,
                 B0010,
                 B0010,
                 B0010,
                 B0001,
                 B0001,
                 B0001}; 

//                   abcd
int fullStep[12] = {B0110,
                    B0011,
                    B0011,
                    B1001,
                    B1001,
                    B1100,
                    B0110,
                    B0110,
                    B0111,
                    B0011,
                    B1001,
                    B1001};

//                   abcd
int halfStep[9] = { B0001,
                    B1001,
                    B1000,
                    B1100,
                    B0100,
                    B0110,
                    B0010,
                    B0011,
                    B0001};

                      

void setup() {
//               76543210
  DDRD = DDRD | B00111100; // Set pins 2-5 as outputs
}

void loop(){
  if(count < countsperrev) {
    clockwise();
    count++;
  } else {
    delay(700);
    count = 0; 
  }
}

void clockwise()
{
  for(int i = 8; i >= 0; i--)
  {
    // Set the pin states for this step
    PORTD = (halfStep[i] << 2);
    delayMicroseconds(motorSpeed);
  }
  // Set all pins low
  PORTD = (B0000 << 2);
}