You just need to write a function called interrupt. If you are going to use priority levels on interrupts, high priority interrupt service routines are described in void interrupts(void) function, and low level interrupts are described in void interrupts_low(void) function. To check for the correct interrupts, use if checking statement for set interrupt flags.
Example of Timer0 interrupt for PIC mcu:
Code:
void interrupt()
{
if(TMR0IF_bit) // TIMER0 interrupt
{
TMR0IF_bit = 0; // clear TIMER0 overflow interrupt flag bit
// interrupts service routine's for TIMER0 interrupt functions go here
}
}