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width between two pulses

 
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ahmad-al3omar



Joined: 25 May 2007
Posts: 16

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width between two pulses
PostPosted: Wed Feb 13, 2008 3:19 am     Reply with quote
hello all;
i am trying to calculate the time difference between two pulse waves , i am using the the pic18f458 and i connect each pulse wave to interrupt 0 and interrupt 1 and i use timer1 to calculate the time between two edges
i am using the following code :

Code:
#include<18f458.h>
#fuses noprotect,nowdt,xt
#use delay(clock=4000000)
#include<lcd.c>

int value;
#int_ext
ext1_isr()
{
set_timer1(0);
}

#int_ext1
ext2_isr()
{
value=get_timer1();
lcd_gotoxy(1,2);
printf(lcd_putc,"value=  %d            ",value);
}



main()
{
lcd_init();
enable_interrupts(global);
enable_interrupts(int_ext1);
enable_interrupts(int_ext2);
setup_timer_1(t1_internal|t1_div_by_8);
ext_int_edge( l_TO_h);
ext_int_edge( 1, l_TO_h);
while(1)
{
lcd_gotoxy(1,1);
printf(lcd_putc,"value=  %d            ",value);
}

}



but the output value on the lcd is changed rapidly and not constant on the simulation .
can you help me to find out the way to calculate the difference ???
thank you all
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kolio



Joined: 06 Feb 2008
Posts: 26

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PostPosted: Wed Feb 13, 2008 2:24 pm     Reply with quote
Hi Ahmad,

Don't use lcd_gotoxy() and printf() in ISR. Read about "re-entrant code".
Try this one:
Code:

#include<18f458.h>
#fuses noprotect,nowdt,xt
#use delay(clock=4000000)
#include<lcd.c>

int value;
int1 Completed;
#int_ext
ext1_isr()
{
if(!Completed) set_timer1(0);
}

#int_ext1
ext2_isr()
{
value=get_timer1();
Completed = 1;
//lcd_gotoxy(1,2);
//printf(lcd_putc,"value=  %d            ",value);
}



main()
{
lcd_init();
Completed = 0;
enable_interrupts(global);
enable_interrupts(int_ext1);
enable_interrupts(int_ext2);
setup_timer_1(t1_internal|t1_div_by_8);
ext_int_edge( l_TO_h);
ext_int_edge( 1, l_TO_h);
while(1)
{
if(Completed){
lcd_gotoxy(1,1);
printf(lcd_putc,"value=  %d            ",value);
Completed = 0;
}
}

}


In this way you may miss some pulses during printing the result on LCD, but the measurement will be properly displayed. Also pay attention about the duration and edges of the pulses.
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