David
Serial ports are fickle things, particular when you are talking about
"embedded" microcontroller peripherals. Most circuit designers tend to try
and get away with the minimal number of components (to fit in a given size
box) and the minimal number of "wasted" pins on the processor (to keep to
the smallest IC package possible), and of course the accountants want you
to use the cheapest and lowest part count to keep the cost down and
maximise profits. Crystals are comparatively expensive compared to many
other parts.
One of the tradeoffs in the embedded world is whether you use one crystal
oscillator for the processor clock, and try and divide that down to give
you your UART (serial port) clock on the processor's serial port, or
whether you put a second crystal on specifically to get the baud rates spot
on because it divides nicely (or try to use that one on its own for the
processor clock too).
If you choose two crystals, life is easy except for the added cost and
possibly the loss of a few pins on your processor - OK if you've got
spares, but not so good if you're trying to cram every last function onto
your processor of choice.
If you choose one crystal, and you go with a "nice" crystal you may find
that other things like maintaining a nice internal clock to count time
periods e.g. 10 msec intervals, might not be easy to obtain by division.
If you choose one crystal, and go with one that works good for your timing
needs, e.g a crystal that is a whole number of MHz, then you may only be
right-on for several baud rates, and the error is quite high for others.
Here's one web site that talks about it from the perspective of the popular
Intel 8051 family
http://www.pjrc.com/tech/8051/autobaud.html
I suspect that the EW logger may be a little bit off from the correct baud
rate clock, and if the USB to RS-232 converter you are using is also "off"
in the opposite direction, then when connected together, the two UARTs
might just be far enough out of whack that they cannot read each others
transmissions reliably. A bit like having two radios that are both
off-frequency by a few hundred kHz. But, unlike the incredible human brain
that can decode speech from a lot of background hash, the humble UART
simply loses the plot and generates framing or parity errors.
Good luck, and like I said before, give the Dontronics EasySync cable a go.
Cheers
Jason Armistead
At 09:22 AM 31/10/2005, you wrote:
Peter,
Did the Belkin work with an EW logger? The EW seems to be particularly
sensitive in its dealings with Serial ports - I suspect the problem is not
just
the USB adapter; the EW plays a part as well.
Regards,
David Villiers
VH-GMP
Quoting Peter Stephenson <[EMAIL PROTECTED]>:
Sadly, the Dolphin did NOT work despite flashing it's light but a
borrowed Belkin adaptor did. :-)
PeterS
----- Original Message ----- From: "Peter Stephenson"
<[EMAIL PROTECTED]>
To: "Discussion of issues relating to Soaring in Australia."
<aus-soaring@lists.internode.on.net>
Cc: "DDSC chat" <[EMAIL PROTECTED]>
Sent: Tuesday, October 25, 2005 10:12 AM
Subject: Re: [Aus-soaring] EW Logger and USB-Serial Adapters
I have a Dolphin one from Dick Smiths that communicates with WinXP home,
Compaq 700, a Colibri and SeeYou but did not get round to checking that
it works 100% as I ran out of time but will be testing it again this
week if the strip at DDSC becomes flyable after a huge storm last night
leaving the
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