請教各位 PIC18F26K20 timer ISR 函式如何撰寫？寫成如下函式，但發現執行時並未進入 isr，且 ulTickCount 的值未更新。

#pragma config WDTEN = OFF
#pragma config FOSC = INTIO67

ULONG ulTickCount;

void main (void)
{
int i;

// Internal OSC setup
//
OSCCON |= 0x70; // 16 MHZ
while ((OSCCON & BIT2) == 0); // wait for stable

INTCON = 0x20; //disable global and enable TMR0 interrupt
//INTCON2 = 0x84; //TMR0 high priority
INTCON2 = 0x04; //TMR0 high priority
RCONbits.IPEN = 1; //enable priority levels
TMR0H = 0; //clear timer
TMR0L = 0; //clear timer
T0CON = 0x82; //set up timer0 - prescaler 1:8
INTCONbits.GIEH = 1; //enable interrupts


while (1);
}

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

#pragma code
#pragma interrupt InterruptHandlerHigh

void
InterruptHandlerHigh ()
{
if (INTCONbits.TMR0IF)
{ //check for TMR0 overflow
INTCONbits.TMR0IF = 0; //clear interrupt flag
ulTickCount++;
}
}

//----------------------------------------------------------------------------
// High priority interrupt vector

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

//----------------------------------------------------------------------------