Getting Started

Chapter 7: Microcontroller Interrupts and Timers

r

timer2 counter

ag

F2A)) );

sei(); // __enable_interrupt(); // enable global interrupt

if ( (TIFR1 && (1<<TOV1)) )

verflows, set the temp to 0xFFFF

the timer1 counter value

tempL = TCNT1L;

temp = TCNT1H;

increase OSCCAL
}
else
calibrate = TRUE; // the interRC is correct

TCCR1B = (1<<CS10); // start timer1
}
}

OSCCAL_calibration() function – detailed explanation

he ‘System Clock and Clock Options’ section of the ATmega169 data book tells

TCNT1H = 0; // clear timer1 counte
TCNT1L = 0;
TCNT2 = 0; // clear

// wait for timer2 comparefl
while ( !(TIFR2 && (1<<OC

TCCR1B = 0; // stop timer1

{
temp = 0xFFFF; // if timer1 o
}
else
{ // read out

temp = (temp << 8);
temp += tempL;
}

if (temp > 6250)
{
OSCCAL--; //RC oscillator runs to fast, decrease OSCCAL
}
else if (temp < 6120)
{
OSCCAL++;//RC oscillator runs to slow,

T

more than you’ll ever want to know about the ATmega169's clock. Let’s focus on
only what we need for our system.