Getting Started

Chapter 8: C Pointers and Arrays

porary variable and shift it right by 8

t that we

te for the

en a 1 MHz

as used in the original Butterfly code.

= 7;

lly top value low byte and adjust it for the 2 MHz clock.

e Timer0 interrupt calls the Play_Tune function every 10

before:

re value

caler

temp_hi = pgm_read_word(pSong + Tone); // read out the PWM-value

The Tone is an integer, so we get it into a tem
bits and load that value into the high byte of the counter top. Excep
actually only shift it right by 7 bits to adjust it (cut it in half) to compensa
use of a 2MHz system clock in this applications (for the USART) wh
clock w

temp_hi >>

We clear the Timer1 count.

TCNT1H = 0;
TCNT1L = 0;

We load the counter top value high byte.

ICR1H = temp_hi;

Fina we load the counter

ICR1L = pgm_read_word(pSong + Tone);
ICR1L <<= 1;

Using the Timer0 interrupt to play a tune

As mentioned above th
ms. We set up the Timer0 much as we’ve seen

// Enable timer0 compare interrupt
TIMSK0 = (1<<OCIE0A);

// Sets the compa
OCR0A = 38;

// Set Clear on Timer Compare (CTC) mode, CLK/256 pres
TCCR0A = (1<<WGM01)|(0<<WGM00)|(4<<CS00);