/*
  Example Code for a simple R2R-DA on Port D
 
  This example code is in the public domain.
 */

unsigned char sinus[256];
unsigned char x = 0;
unsigned char y = 0;


void setup() {                

  // initialize PORT D as output port
  DDRD = 0xff;

  // initialize timer1 
  noInterrupts();           // disable all interrupts

  TCCR1A = 0;
  TCCR1B = 0;
  TCNT1  = 0;

  OCR1A = 3;            // compare match register for timing
  TCCR1B |= (1 << WGM12);   // CTC mode
  TCCR1B |= (1 << CS11);    // CS10 = no prescaler, CS11 = 8, CS12 = 256, CS11|CS10 = 64, CS12||CS10 = 1024
  TIMSK1 |= (1 << OCIE1A);  // enable timer compare interrupt
  
  interrupts();             // enable all interrupts

  // For some reason, this code must be here or the output will not work
  for(unsigned char i=0;i<256;i++)
    sinus[i]=(unsigned char) ((float)sin((2*PI*i)/255) *127.0 + 127.0);

}

ISR(TIMER1_COMPA_vect)
{
  // DC - for measurement of voltage at specific steps
  //PORTD = 128;  

/*
  // Triangle
  if(!y) // aufwärts zählen
  {
    x++;
    if(x == 255)
      y = 1;
  }
  else // abwärts
  {
    x--;
    if(x == 0)
      y = 0;
  }
  PORTD = x;
*/

  // Sinus
  PORTD = sinus[x++];
}

void loop() {
}