SPWM using Arduino Mega2560

#define MAX_COUNT 308    // (16 MHz / SW_FREQ) / 2 = 16000000 / 26000 = 615 / 2 = 308
#define NO_OF_PULSES 260 // 26 kHz / 50 Hz = 520; 520 / 2 = 260 pulses in one half-cycle

const int lookUp[NO_OF_PULSES] = {
  0, 4, 7, 11, 15, 19, 22, 26, 30, 33, 37, 41, 45, 48,
  52, 56, 59, 63, 66, 70, 74, 77, 81, 84, 88, 92, 95,
  99, 102, 106, 109, 113, 116, 120, 123, 126, 130, 133,
  137, 140, 143, 146, 150, 153, 156, 159, 163, 166, 169,
  172, 175, 178, 181, 184, 187, 190, 193, 196, 199, 201,
  204, 207, 210, 212, 215, 218, 220, 223, 226, 228, 231,
  233, 235, 238, 240, 242, 245, 247, 249, 251, 253, 256,
  258, 260, 262, 264, 265, 267, 269, 271, 273, 274, 276,
  278, 279, 281, 282, 284, 285, 287, 288, 289, 291, 292,
  293, 294, 295, 296, 297, 298, 299, 300, 301, 302, 302,
  303, 304, 304, 305, 305, 306, 306, 307, 307, 307, 307,
  308, 308, 308, 308, 308, 308, 308, 308, 308, 307, 307,
  307, 307, 306, 306, 305, 305, 304, 304, 303, 302, 302,
  301, 300, 299, 298, 297, 296, 295, 294, 293, 292, 291,
  289, 288, 287, 285, 284, 282, 281, 279, 278, 276, 274,
  273, 271, 269, 267, 265, 264, 262, 260, 258, 256, 253,
  251, 249, 247, 245, 242, 240, 238, 235, 233, 231, 228,
  226, 223, 220, 218, 215, 212, 210, 207, 204, 201, 199,
  196, 193, 190, 187, 184, 181, 178, 175, 172, 169, 166,
  163, 159, 156, 153, 150, 146, 143, 140, 137, 133, 130,
  126, 123, 120, 116, 113, 109, 106, 102, 99, 95, 92, 88,
  84, 81, 77, 74, 70, 66, 63, 59, 56, 52, 48, 45, 41, 37,
  33, 30, 26, 22, 19, 15, 11, 7, 4
};

const int lookUp2[NO_OF_PULSES] = {
  1, 5, 8, 12, 16, 20, 23, 27, 31, 34, 38, 42, 46, 49, 53,
  57, 60, 64, 67, 71, 75, 78, 82, 85, 89, 93, 96, 100, 103,
  107, 110, 114, 117, 121, 124, 127, 131, 134, 138, 141, 144,
  147, 151, 154, 157, 160, 164, 167, 170, 173, 176, 179, 182,
  185, 188, 191, 194, 197, 200, 202, 205, 208, 211, 213, 216,
  219, 221, 224, 227, 229, 232, 234, 236, 239, 241, 243, 246,
  248, 250, 252, 254, 257, 259, 261, 263, 265, 266, 268, 270,
  272, 274, 275, 277, 279, 280, 282, 283, 285, 286, 288, 289,
  290, 292, 293, 294, 295, 296, 297, 298, 299, 300, 301, 302,
  303, 303, 304, 305, 305, 306, 306, 307, 307, 308, 308, 308,
  308, 309, 309, 309, 309, 309, 309, 309, 309, 309, 308, 308,
  308, 308, 307, 307, 306, 306, 305, 305, 304, 303, 303, 302,
  301, 300, 299, 298, 297, 296, 295, 294, 293, 292, 290, 289,
  288, 286, 285, 283, 282, 280, 279, 277, 275, 274, 272, 270,
  268, 266, 265, 263, 261, 259, 257, 254, 252, 250, 248, 246,
  243, 241, 239, 236, 234, 232, 229, 227, 224, 221, 219, 216,
  213, 211, 208, 205, 202, 200, 197, 194, 191, 188, 185, 182,
  179, 176, 173, 170, 167, 164, 160, 157, 154, 151, 147, 144,
  141, 138, 134, 131, 127, 124, 121, 117, 114, 110, 107, 103,
  100, 96, 93, 89, 85, 82, 78, 75, 71, 67, 64, 60, 57, 53, 49,
  46, 42, 38, 34, 31, 27, 23, 20, 16, 12, 8, 5
};

volatile bool positiveHalf = false;
volatile bool positiveHalf3 = false;

void setup()
{
  pinMode(2, OUTPUT);
  pinMode(5, OUTPUT);
  pinMode(10, OUTPUT);
  pinMode(11, OUTPUT);
  pinMode(12, OUTPUT);
  pinMode(50, OUTPUT);
  // Timer1 Registers initialisation, see datasheet for more detail.
  TCCR1A = 0;
  TCCR1B = 0;
  TCCR3A = 0;
  TCCR3B = 0;
  TCCR1A = 0b10110000;       // Set OC1A (pin D9) on Compare Match; Disconnect OC1B (pin D10); PWM, Phase and Frequency Correct (Mode 8);
  TCCR1B = 0b00010001;       // PWM, Phase and Frequency Correct (Mode 8); Clock Select = System clock (No Prescaling) [Ref. Data Sheet, p. 132]
  ICR1 = MAX_COUNT;          // Period for 16MHz crystal, for a switching frequency of 16 kHz for 320 subdevisions per 50 Hz sin wave cycle.
  TCCR3A = 0b10110000;       // Set OC1A (pin D9) on Compare Match; Disconnect OC1B (pin D10); PWM, Phase and Frequency Correct (Mode 8);
  TCCR3B = 0b00010001;       // PWM, Phase and Frequency Correct (Mode 8); Clock Select = System clock (No Prescaling) [Ref. Data Sheet, p. 132]
  ICR3 = MAX_COUNT;          // Period for 16MHz crystal, for a switching frequency of 16 kHz for 320 subdevisions per 50 Hz sin wave cycle.
  OCR1A = lookUp[0];
  OCR1B = lookUp2[0];
  OCR3A = lookUp[0];
  OCR3B = lookUp2[0];
  TIMSK1 = 0b00000001;       // TOIE1 = 1: Overflow Interrupt Enable
  TIMSK3 = 0b00000001;    // TOIE3 = 1: Overflow Interrupt Enable
  sei();                     // Enable global interrupts.
}

void loop()
{
  // place any code you want
}

ISR(TIMER1_OVF_vect)
{
  static int i = 1;       // Static means it will NOT be reinitialized
  if (i >= NO_OF_PULSES) {
    i = 0;
  }

  if (positiveHalf == true) {
    OCR1A = lookUp[i];
    OCR1B = lookUp2[i];
  } else {
    OCR1A = 0;
    OCR1B = 0;
  }

  if (i == 1) {
    positiveHalf = !positiveHalf;
    OCR1A = 0;
    OCR1B = 0;
  }
  i++;

}

ISR(TIMER3_OVF_vect)
{
  static int j = 1;       // Static means it will NOT be reinitialized
  if (j >= NO_OF_PULSES) {
    j = 0;
  }
  if (positiveHalf3 == false) {
    OCR3A = lookUp[j];
    OCR3B = lookUp2[j];
  } else {
    OCR3A = 0;
    OCR3B = 0;
  }
  if (j == 1) {
    positiveHalf3 = !positiveHalf3;
    OCR3A = 0;
    OCR3B = 0;
  }
  j++;
}