Page 255 - Mechatronics with Experiments

MICROCONTROLLERS 241
Example: Timer0 Interrupt Below is a sample code which sets up Timer0 to
generate interrupt. Timer0 is defined as a low priority interrupt. Interrupt vector table
location for low priority interrupts is 000018h . As in the previous example, a shell form of
low priority ISR for a low priority interrupt address is placed at the 0x18 vector address,
and “goto” statement is used to direct the program execution to the Timer0 ISR.

#include <p18f452.h> /∗ Header file for PIC 18F452 register declarations ∗/
#include <timer.h> /∗ For timer interrupt ∗/

/∗ Interrupt Service Routine (ISR) logic ∗/
void Timer0_ISR(void) ;

#pragma code LOW_INTERRUPT_VECTOR = 0x18
/∗ Specify where the program address to be stored ∗/

void Low_ISR(void)
{
_asm
goto Timer0_ISR
_endasm
}
#pragma code /∗ Restore the default program memory allocation. ∗/

#pragma interruptlow Timer0_ISR
void Timer0_ISR(void)
{
static unsigned char led_display = 0;

INTCONbits.TMR0IF = 0;
led_display = ˜led_display & 0x0F /∗ toggle LED display ∗/
PORTB = led_display ;

}

/∗ Setup of the ISR ∗/
void EnableInterruptTimer0(void)
{
TRISB = 0;
PORTB = 0;
OpenTimer0 (TIMER_INT_ON & TO_SOURCE_INT & TO_16BIT) ;
INTCONbits.GIE = 1;
}

void main (void)
{

EnableInterruptTimer0() ;
while (1) ; /∗ Wait indefinitely. ∗/
/∗ when the interrupt occurs,
the corresponding ISR will be executed ∗/
}