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Timer 0 problem

 
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Guest
Timer 0 problem
PostPosted: Fri Mar 14, 2008 4:07 am     Reply with quote
Hi

Why is Timer_0 int not 256us.
When I mesure on A1(the pin there are toogled in the int) there are 1khz -> 2*500us. But I expect 2*256us -> 2khz??

What is wrong here??
___

Code:
#include <18F2455.h>

#FUSES NOWDT             
#FUSES INTXT             
#FUSES NOBROWNOUT
#FUSES PUT                     
#FUSES MCLR                   

#use delay(clock=4000000)
#use rs232(baud=19200,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8,stream=com1, errors)
 
//*** led pin assign
#define led_hw_r PIN_A0
#define led_hw_g PIN_A1

//*** led macro
#define led_g_toogle output_toggle(led_hw_g)
#define led_r_on_off(on) output_bit (led_hw_r, on)
#define led_g_on_off(on) output_bit (led_hw_g, on)

 
#int_TIMER0
void  Timer_0_int(void) {
 led_g_toogle; //I expec 256 us but there are 510 us??
}


void flashled(){
 led_r_on_off(1);
 delay_ms(100);
 led_r_on_off(0);
 delay_ms(300);
}

void main(){
  int cnt=0; 
 
  setup_oscillator(OSC_4MHZ|OSC_INTRC|OSC_31250|OSC_PLL_OFF);
  setup_adc_ports(NO_ANALOGS|VSS_VDD);
     
  setup_wdt(WDT_OFF);
  setup_timer_0(RTCC_INTERNAL|RTCC_8_bit);//1u*256 = 256us.
  setup_timer_1(T1_DISABLED);
  setup_timer_2(T2_DISABLED,0,1);
     
  enable_interrupts(INT_TIMER0);
  enable_interrupts(GLOBAL);
   
 fprintf(com1,"Reset...!\r\n");

 while (1){
  flashled();
  cnt++;
  fprintf(com1," ok:%u ",cnt);
 }
}//main//



I need some help on this.
Guest
PostPosted: Fri Mar 14, 2008 7:47 am     Reply with quote
Problem is fixed!

I think it confusing that the RTCC_DIV_1 must be included.

I found the error when looking at the T0CON bit3 was not set.

That wil say T0CON_bit3 = PSA = RTCC_DIV_1.

setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1|RTCC_8_bit);//1u*256 = 256us.

Just for information :-)
Matro
Guest
PostPosted: Fri Mar 14, 2008 7:52 am     Reply with quote
Is your Xtal really a 4MHz one?

Matro
Guest
PostPosted: Fri Mar 14, 2008 8:14 am     Reply with quote
Hi

I use the internal CLK at 4 mhz.
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