Phil,

On Sun, 8 May 2005 16:19:12 -0700 (PDT), phil B wrote:

>...<
> What I'm seeing is that the DS1302 is not off by
> a constant amount but drifts around by as much as 30
> seconds + or - in a day.  That is to say one day the
> RTC will be ahead by 20-30 seconds and the next day it
> will be behind by some amount.  The room that its in
> stays within 5 degrees F and I haven't gotten
> physically near (2-3 ft) the circuit in question (I'm
> using a PIC to send the time via serial I/O).  The
> circuit is in a solderless breadboard so I know there
> is extra capacitance probably slowing the crystal
> down.
> 
> So, I would have though under those circumstances, the
> RTC would be off by a relatively fixed percentage.  Is
> this just a case of the solderless BB causing problems
> or is there something else going on?  something that I
> might compensate for?  
> 
> The PCB its going into has ground rings on both sides
> of the board for the crystal, I've routed signals away
> from the RTC in general and the crystal in particular
> and have lots of grounded copper areas. 

I'm confused - you say you are using solderless breadboard, then talk about PCB tracks - can you describe the 
setup in its entirety, which may give us a clue as to the culprit?  I suspect it could be interference being 
picked up somewhere (possibly from the serial lines, as you say they are long) and this is causing extra or 
missed cycles.

Cheers,


Howard Winter
St.Albans, England


-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist