PIC18F2321 TIMR0 issue

[chimera786]

Hey there!

This is my first time messing with the 18F series. This uC is definitely powerful.. in fact an overkill for the applications that I have been/am developing.

So, I decided to baby step this uC just because the datasheet is long and had way too many jam packed features.

I have been trying to get the TMRO to work with a simple PORTB toggle. But it doesn't seem to be working. I have looked high and low thru the datasheet but it doesn't look like im missing anything

I am probing the output of PORTB with a o-scope but the thing is that I am getting a constant square wave of 490Hz.

Basically, the timer0 is expiring at the wrong interval, rather than expiring at the freq i want it to

Please take a look at it guys-- its so simple that i cant find it..maybe Ive overlooked something.. maybe im not configuring some registers correctly..

void main() {
     
     OSCTUNE=0x00;
     OSCCON=0xCE;// oscillator at 1Mhz
     ADCON1=0xFF;// Make sure pins are IOs

     INTCON=0xA0;// Global + TMR0 interrupt ON

     T0CON=0xC8;// Configure TMR0 as 8bit no prescale
     TMR0L=100;

     TRISB=0x00;// PORTB as OUTPUT
     PORTB=0;
     
}

void interrupt (void) {

    if (INTCON.B2){
                   INTCON.B2=0;
                   PORTB=~PORTB;
    }

}

 

[Tahmid]

Since you say that the timing is off, my guess is that your timing output sets an output frequency of ~750Hz.

Make these two changes (I've shown them in the code):

• Add an infinite loop in the code.
• Reload TMR0 each interrupt.

void main() {
     
     OSCTUNE=0x00;
     OSCCON=0xCE;// oscillator at 1Mhz
     ADCON1=0xFF;// Make sure pins are IOs

     INTCON=0xA0;// Global + TMR0 interrupt ON

     T0CON=0xC8;// Configure TMR0 as 8bit no prescale
     TMR0L=100;

     TRISB=0x00;// PORTB as OUTPUT
     PORTB=0;
     [B][COLOR="#FF0000"]while(1);[/COLOR][/B]
}

void interrupt (void) {

    if (INTCON.B2){
                   INTCON.B2=0;
                   PORTB=~PORTB;
                   [B][COLOR="#FF0000"]TMR0L = 100;[/COLOR][/B]
    }

}

Hope this helps.
Tahmid.