>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] 
>On Behalf Of Andre Abelian
>Sent: 26 July 2007 21:13
>To: Microcontroller discussion list - Public.
>Subject: [PIC] sync problem
>
>
>Hi to all,
>
>well same project came back with sync problem. One of the pin 
>is requesting data every 8 ms and data I have to send when it 
>does high then low transition. When I added interrupt routine 
>I got the speed but it was out if sync very little. what I did 
>is in ISR I set variable to set 1 when it sending data and in 
>while loop since ADC and MATH routines are slow by using if 
>statement I was able sync them together. At this moment it is 
>working but I worry about if the method I came up is reliable. 
>see code below
>
>
>/////////////////////////////////////////////////
>// Read ADC and Send all 6 bytes out 
>/////////////////////////////////////////////////
>#int_rtcc 
>void output_data_isr()
>   {
>        set_timer0(0xFF00);
>        sft_trigger = 0;    
>        if (!input(trigger))               // wait for ttl 
>input pressed active low (was B2)
>              {
>        while(!input(trigger)){}           // wait for release


This seems dangerous, you are waiting within the ISR for a transition on a pin.  If this transition is late, your watchdog timer will reset the PIC.  It would probably be a better idea to use a simple state machine inside the ISR to handle edge detection.

Do you have anything in place to prevent the ISR sending the data whilst it's being written by the main loop?  

How often is your timer interrupt occuring?  How long is the incomming pulse?  The code mentions "was B2", which pin are you polling now?

Regards

Mike

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