Hi,

The C18 example states that an interrupt handler is to be defined thus:
(in MCC18\examples\Interrupt\main.c)
//-------------------------------------------------------------------------=
---
// High priority interrupt vector

#pragma code InterruptVectorHigh =3D 0x08
void
InterruptVectorHigh (void)
{
  _asm
    goto InterruptHandlerHigh //jump to interrupt routine
  _endasm
}

//-------------------------------------------------------------------------=
---
// High priority interrupt routine

#pragma code
#pragma interrupt InterruptHandlerHigh

void
InterruptHandlerHigh ()
{
  if (INTCONbits.TMR0IF)
    {                                   //check for TMR0 overflow
      INTCONbits.TMR0IF =3D 0;            //clear interrupt flag
      Flags.Bit.Timeout =3D 1;            //indicate timeout
      LATBbits.LATB0 =3D !LATBbits.LATB0; //toggle LED on RB0
    }
}


But I can't seem to figure out why that INTCONbits.GIEH is disabled
after once it has run through the handler. In asm, the Global Interrupt
handler is enabled after a retfie, but with C18 and the 18F4550, this
doesn't seem to be the case, I do need a retfie as follows, for the
interrupt to be re enabled. Any idea why it is thus ?

Additionally, I have this question, the ISR is unconditionally jumping to
another function. Especially in an ISR, I can't really reason why that
would be a good practice ?  (Although I can assume that the functions
would expand to labels in asm. But still doesn't explain the missing retfie=
)



void low_isr(void)
{
    if ((PIE1bits.TMR2IE =3D=3D 1) && (PIR1bits.TMR2IF =3D=3D 1)) {
        PIR1bits.TMR2IF =3D 0;
               DisplayDigit(segment, display[segment]);
    }
    _asm
        retfie 0
    _endasm
}

#pragma code low_vector =3D 0x18
void low_vector (void)
{
    _asm goto low_isr _endasm
}

void init_timer2(void)
{
    OpenTimer2(TIMER_INT_ON & T2_PS_1_4 & T2_POST_1_1);
     PR2 =3D 223;
    RCONbits.IPEN    =3D 1; /* Interrupt priority enable */
        IPR1bits.TMR2IP    =3D 0; /* TMR2 Low priority */
     INTCONbits.GIEL =3D 1;
       INTCONbits.GIEH =3D 1;
}

void main()
{
    TRISD =3D 0;
    TRISC =3D 0;
    init_timer2();

    while (1) {

        }
}

Thanks,
Manu
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.