11.9 Interrupt Setup Procedure

  1. When using interrupt priority levels, set IPEN and then select the user-assigned priority level for the interrupt source by writing the control bits in the appropriate IPRx control register.
    Important: At a device Reset, the IPRx registers are initialized such that all user interrupt sources are assigned to high priority.
  2. Clear the Interrupt Flag Status bit associated with the peripheral in the associated PIRx STATUS register.
  3. Enable the interrupt source by setting the interrupt enable control bit associated with the source in the appropriate PIEx register.
  4. If the vector table is used (MVECEN = 1), then set up the start address for the Interrupt Vector Table using IVTBASE. See the Interrupt Vector Table Contents section for more details.
  5. Once IVTBASE is written to, set the interrupt enable bits in INTCON0.
  6. An example of setting up interrupts and ISRs can be found below.

Setting Up Vectored Interrupts Using XC8

// NOTE 1: If IVTBASE is changed from its default value of 0x000008, then the
// "base(...)" argument must be provided in the ISR. Otherwise the vector
// table will be placed at 0x0008 by default regardless of the IVTBASE value.

// NOTE 2: When MVECEN=0 and IPEN=1, a separate argument as "high_priority"
// or "low_priority" can be used to distinguish between the two ISRs.
// If the argument is not provided, the ISR is considered high priority
// by default.

// NOTE 3: Multiple interrupts can be handled by the same ISR if they are
// specified in the "irq(...)" argument. Ex: irq(IRQ_SW, IRQ_HLVD)

void __interrupt(irq(IRQ_SW), base(0x3008)) SW_ISR(void)
    PIR0bits.SWIF = 0;    // Clear the interrupt flag
    LATCbits.LATC0 ^= 1;    // ISR code goes here
void __interrupt(irq(default), base(0x3008)) DEFAULT_ISR(void)
    // Unhandled interrupts go here
void INTERRUPT_Initialize (void)
    INTCON0bits.GIEH = 1;    // Enable high priority interrupts
    INTCON0bits.GIEL = 1;    // Enable low priority interrupts    
    INTCON0bits.IPEN = 1;    // Enable interrupt priority
    PIE0bits.SWIE = 1;     // Enable SW interrupt
    PIE0bits.HLVDIE = 1;     // Enable HLVD interrupt
    IPR0bits.SWIP = 0;     // Make SW interrupt low priority

    // Change IVTBASE if required
    IVTBASEU = 0x00;          // Optional
    IVTBASEH = 0x30;          // Default is 0x000008
    IVTBASEL = 0x08;