C18, PIC18F252: Setting timer0 with an interrupt ?

Question

Hi all...I'm trying to set up timer0 to time about 10ms and inc a global variablethat gets displayed on an LCD. Everything is pretty much working except thatI can't change the time out value for timer0. I init the timer before  awhile loop that display the variable "time". The isr inc the value on everytime out of timer0. It also toggles RB4 so I can check the freq (fortesting). The freq is always about 4 Hz.TIME_TIMEOUT is defined as 5000. I've tried to change this value but nothinghappens. What am I missing ?ThanksBTW it runs at 2MHz. There is only one isr.//------------- code begins -------------------------- OpenTimer0(TIMER_INT_ON & T0_16BIT & T0_SOURCE_INT & T0_PS_1_1); WriteTimer0(TIME_TIMEOUT);// INTCON=0;    //make sure interrupts are disable//   //enable global interrupts//   //enable peripheral interrupts//  //enable TMR0 overflow interrupt enable bit INTCON=0xe0;   //all 4 lines above combined while(1) {  itoa(time,timeStr);  SetDDRamAddr(LCD_LINE2); // Display value of time  while(BusyXLCD());   // Wait if LCD busy  putsXLCD(timeStr); };//--------------- code ends ----------------------The isr is here://------------- code begins ----------------------#pragma code#pragma interrupt InterruptHandlerLowvoid InterruptHandlerLow(){ if ( {  time++;  PORTBbits.RB4=~PORTBbits.RB4;  WriteTimer0(TIME_TIMEOUT);            //clear interrupt flag }}//--------------- code ends ----------------------

Grog · Accepted Answer

thateverynothingHmmm something smells.......2Mhz(Xtal) / 4(CLK0) / 4(Prescaler) / 16384(16bit count) / 2(Port bittoggle)=  "about 4Hz"I like Gary Kato's question.Greg the Grog

Rodo · Answer

Here is the source code:/* $Id: t0write.c,v 1.2 2000/08/04 20:58:59 ConnerJ Exp $ */#include #include /********************************************************************* Function Name: WriteTimer0 ** Return Value: void ** Parameters: int: value to write to Timer0 ** Description: This routine writes a 16-bit value to Timer0 ** Timer0. *********************************************************************/void WriteTimer0(unsigned int timer0){union Timers timer; = timer0; // Copy timer value into unionTMR0H =  // Write low byte to Timer0TMR0L =  // Write high byte to Timer0}Thanks

Gary Kato · Answer

Shouldn't you be using | instead of & here?

Guillaume · Answer

Nope, that's Microchip's C18 way of expressing constant flags.They are defined accordingly so you can combine them with '&'.A bit confusing, I agree.

Rodo · Answer

I found my error. This micro triggers an interrupt when the count goes from ffff to 0000. The delay of 10ms would need :

(2MHz/4(sclk))^-1=2us now

10ms/2us=5000 so ...

the timer should count 5000 times before it triggers the int. So :

16bit counter -1 = 65535. I need 5000, so the value should have been 60535 (and not 5000). It works :-)! I was used to the zilog z8 where the counters count down.

Thanks

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every

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C18, PIC18F252: Setting timer0 with an interrupt ?

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