Getting Started

Chapter 7: Microcontroller Interrupts and Timers

SCCAL_calibration() function – the code:

*************************************************

ameters : None

CLKPR = (1<<CLKPCE); // set Clock Prescaler Change Enable

hz / 8 = 1Mhz

;

TI e OCIE2A and TOIE2

timer2

OC // set timer2 compare value

TIMSK0 = 0; // delete any interrupt sources

aling

aling

i(); // mt __disable_interrupt(); // disable global

interrupt

te TIFR1 flags

e TIFR2 flags

O

/**

• 
  


• Function name : OSCCAL_calibration


• 
  


• Returns : None


• 
  


• Par


• 
  


• Purpose : Calibrate the internal OSCCAL byte, using the external


• 32,768 kHz crystal as reference


• 
  

  ***/
  void OSCCAL_calibration(void)
  {
  unsigned char calibrate = FALSE;
  int temp;
  unsigned char tempL;

  
  

// set prescaler = 8, Inter RC 8M
CLKPR = (1<<CLKPS1) | (1<<CLKPS0)

MSK2 = 0; //disabl

ASSR = (1<<AS2); //select asynchronous operation of

(32,768kHz)

R2A = 200;

TCCR1B = (1<<CS10); // start timer1 with no presc
TCCR2A = (1<<CS20); // start timer2 with no presc

//wait for TCN2UB and TCR2UB to clear
while((ASSR & 0x01) | (ASSR & 0x04));

Delay(1000); // wait for external crystal to stabilise

while(!calibrate)
{
cl

TIFR1 = 0xFF; // dele
TIFR2 = 0xFF; // delet