Registers involved: GPIO: DDRB: Data Direction Register for Port B= 0xFF for output PWM Module: OCR0A: Output Compare Register A=Value here is compared with the Timer value,and when the value matches, the specific pin[pin OC0A(pin 13) in this case] gets toggled TCCR0A: Timer/Counter 0 Control Register A = 0x83 Bit [7:6]= COM0A-Compare Output Mode A = 10-Non-inverting PWM-Clear OC0A on Compare Match Bit [1:0]= WGM[1:0]- Waveform Generation Mode=11- for non-inverting fast PWM. TCCR0B: Timer/Counter 0 Control Register B = 0x03 Bit [2:0] – CS0[2:0]-Clock Select = 011- for prescaler=64 in order to obtain frequency of 1kHz OCR2A: Output Compare Register A=Value here is compared with the Timer value,and when the value matches, the specific pin[pin OC2A(pin 10) in this case] gets toggled TCCR2A: Timer/Counter 2 Control Register A = 0xC3 Bit [7:6]= COM0A-Compare Output Mode A = 11-Inverting PWM-Clear OC2A on Compare Match Bit [1:0]= WGM[1:0]- Waveform Generation Mode=11- for fast PWM. TCCR2B: Timer/Counter 2 Control Register B = 0x04 Bit [2:0] – CS0[2:0]-Clock Select = 100- for prescaler=64 in order to obtain frequency of 1kHz