Thanks Robin & Jan-Erik, that clears it up.  I guess I was thinking about
"jitter".  I can see how a fixed error might work for a very short time,
then the data gets so shifted in time that it's unreadable.  Makes sense.

Thanks again,

-matt





Matt Redmond wrote :

> >> As someone else has mentioned, the baud rate is
> >> irrelevant, the above problem is just as bad at 300
> >>  baud and 19200 baud
>
> Why would that be?  Aren't serial bitwidths wider at lower
> speeds?   Just curious - trying to get an educashun.

Yes they are, but the rellative error (in %) is just the same.
(bit width vs. bit/baud clock error)

Think about it, if you have a 1 meter measuring-tape with
an (known) error of 5% (so it's actualy 1.05 meters long), you will
still get an error of 5% even when measuring 10, 100
or 1000 meters.

In the same way, the *absolute* error in the baudrate clock
will add up and give the same *rellative* error at all baud rates.

It's a whole other thing if you have "jitter" in the baud rate
clock. Jitter tend to even out over time, so in that case lower
baud rates might be "better" then higher. But here we are
talking about a fixed, stable error in the buad rate clock.

Jan-Erik.

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads