PIC18f4520 Timer0 Interrupt Problem

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Amardeep

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Hi
I am Using PIC18f4520 Micro controller.
I want to Generate timer interrupt after every 1sec.
I am using internal clock for timer, Internal oscillator at 125khz, Timer0 in 16-bit Mode
please guide me how to calculate exact value for TH0 and TL0 register

amardeep.singh190@gmail.com
 

You could do it using Timer 0 in 8 bit mode.

125KHz / 4 = 31,250 /* Timer increment frequency. */

1 / 31250 = 0.000032 /* Increment time. */

0.00032 * 256 = 0.008192 /* Using 1:256 prescaler */

1 / 0.008192 = 122 /* counts for 1 second. */

256 - 122 = 134 /* Timer pre load value */

TMR0 = 134

If you pre-load the timer in the interrupt routine, you should have a 1 second interrupt.
Use mplab sim and the stopwatch to fine tune.
 
Thanks Alot .. I Got Every Point ...
 

Hello Btbass

when i simulate the code using MPLAB SIM the time of timer inerrupt is random not fix .. what should be the problem ?
here is attachment of my code View attachment TIMER.txt
 

This is My Code ....

 

Here is a free tool that you can just input the required interrupt frequency into and it will generate all the necessary code to initialise the timer registers for you.

**broken link removed**

Hope this is helpful.

/Pheetuz
 

recheck SCS1:SCS0: System Clock Select bits with data sheet
Because in your code T0CON=0x46;
That means you are using 1:128 prescale value(Fosc/4/128)
T0CS bit=0, Internal instruction cycle clock (CLKO).

The IDLEN bit (OSCCON<7>) controls CPU clocking, while the
SCS1:SCS0 bits (OSCCON<1:0>) select the clock
source.
Check POWER-MANAGED MODES with the datasheet if it is correct
 
Last edited:
You need to pre-load the timer in the interrupt routine so there is a count of 122 before the next interrupt.

Code: 
void TIMER0_ISR(void)
  {
  INTCONbits.TMR0IF = 0; 

  TMR0L = 134;	/* Pre Load timer */ 
  
  ++check;
  
  if(check==0x46)//70
   LED=1;
 
  Delay(); // Millisecond delay
  }
 
thnx evry1 specially @btbass for the big help mate... my problem has been solved... thnx for giving me time n helping in solving the issue.. help appreciated
 

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