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dspic33fj input capture

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Mahdi

Joined: 21 Aug 2012
Posts: 47

dspic33fj input capture

Posted: Tue Mar 31, 2015 8:38 am

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hi buddies

i want to measure duty cycle and freq of pwm signal with 1khz freq with input capture.

my code :

Code:

#include <33FJ256MC710.h>
#use delay(internal=7.37m)
#include <lcd.c>
void main()
{
lcd_init();
setup_timer3(TMR_INTERNAL | TMR_DIV_BY_8);
setup_capture(3, CAPTURE_FE | CAPTURE_TIMER3);
int16 p=0;
while(TRUE)
{

p = get_capture(3,TRUE);
lcd_gotoxy(1,1);
printf(lcd_putc,"%lu",p);

}}

but i have random number on lcd
iam for first to use input capture
can any one help me?
(excuse for poor english)
thank you

Ttelmah

Joined: 11 Mar 2010
Posts: 19372

Posted: Tue Mar 31, 2015 9:18 am

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You have your input signal on pin70?. IC3.
Since you are using capture unit 3, this is where the input has to be.

You really should test for the capture event having happened:

Code:

if (interrupt_active(INT_IC3))
{
//This says an event has happened

//read the captured value, and clear the interrupt
p = get_capture(3,TRUE);
clear_interrupts(INT_IC3);
}

Mahdi

Joined: 21 Aug 2012
Posts: 47

Posted: Tue Mar 31, 2015 10:06 am

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Ttelmah wrote:

You have your input signal on pin70?. IC3.
Since you are using capture unit 3, this is where the input has to be.

You really should test for the capture event having happened:

Code:

if (interrupt_active(INT_IC3))
{
//This says an event has happened

//read the captured value, and clear the interrupt
p = get_capture(3,TRUE);
clear_interrupts(INT_IC3);
}

thank you for reply
yes.on pin 70.pin_d10

but yet lcd show random number

Code:

#include <33FJ256MC710.h>
#use delay(internal=7.37m)
#include <lcd.c>

#INT_IC3
void ic3_isr(void)
{

}
void main()
{
lcd_init();
setup_timer3(TMR_INTERNAL | TMR_DIV_BY_8);
enable_interrupts(INT_IC3);
enable_interrupts(INTR_GLOBAL);
setup_capture(3, CAPTURE_EE | INTERRUPT_EVERY_CAPTURE | CAPTURE_TIMER3);
int16 p=0;
while(TRUE)
{

if (interrupt_active(INT_IC3))
{
//This says an event has happened

//read the captured value, and clear the interrupt
p = get_capture(3,TRUE);
clear_interrupt(INT_IC3);

}
a++;
lcd_gotoxy(1,1);
printf(lcd_putc,"%lu",p);

}}

Ttelmah

Joined: 11 Mar 2010
Posts: 19372

Posted: Tue Mar 31, 2015 10:43 am

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Remember this is a _capture_. You need:

Code:

void main()
{
int16 old=0;
//other init code etc...

//loop etc..
if (interrupt_active(INT_IC3))
{
//This says an event has happened

//read the captured value, and clear the interrupt
p = get_capture(3,TRUE);
clear_interrupt(INT_IC3);
lcd_gotoxy(1,1);
printf(lcd_putc,"%lu",p-old);
old =p;
}

You have to calculate the change between the two capture events, to get the period. Look at ex_capture.c, where this is shown.

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