timer running slow

[himanshu mittal]

sir,

     sir i have configure the timer correctly but my timer running slow nearly at 4 mhz. i have used 16 mhz crystal..i have written proper fuse bits to work with 16 mhz crystal (C9FF).I  have given prescaler to 1024. but i can’t understand the problem..

 

my code is like…

 

//  digital clock using timer–

 

#include<avr/io.h>

#include<avr/interrupt.h>

#include”avr/LCD2014.h”

#define BITx (1<<x)

#define CHECKBIT(x,b) x&b

#define SETBIT(x,b) x|=b

#define CLEARBIT(x,b) x&=~b

#define TOGGLEBIT(x,b) x^=b

#define BIT0 0x01

#define BIT1 0x02

#define BIT2 0x04

#define BIT3 0x08

#define BIT4 0x10

#define BIT5 0x20

#define BIT6 0x40

#define BIT7 0x80

 

unsigned int sec,min,hour,p;

 

ISR(TIMER0_OVF_vect)

{ p++;

  if (p>61)

{

      sec++;

 p=0;

if(sec>59)

{

sec=0;

min++;

if(min>59)

{

min=0;

hour++;

}

}

}

lcd_cmd(0x80) ;

lcd_string(”  “);

lcd_cmd(0x82);

lcd_value(hour);

 

lcd_string(“:”);

 

lcd_value(min);

lcd_string(“:”);

lcd_cmd(0x86);

lcd_value(sec);

 

 

}

 

int main(void)

{

lcd_init();

 p=0; 

sec=0;

min=0;

hour=0;

TIMSK=BIT0;    // enable timer0 overflow interrupt

TCCR0=BIT2|BIT0;     // sert prescaler to 1024 in normal mode

TCNT0=0;

 

sei();

while(1)

{

 

}

}

[AJISH ALFRED]

Hi,

You have included the lcd functions inside the ISR. These functions take more time than the timer firing period, and you will miss a lot of timer interrupts when these functions are executing inside the ISR.

The solution is to keep the lcd functions in the main code.

[Ashutosh Bhatt]

ISR should be as short as possible so as to service next ISR. 

possible solution just update values in ISR dont display

[Author]

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