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PICList Thread
'Auto bauding'
1996\10\15@055708 by Maurice De Jersey

picon face
Hi,

Does anyone have any ideas for implementing auto baud rate detection
on the PIC16C73.  I don't want any switches hanging off my device and
would like it to detect the baud rate anything between 1200 and 57600.

I suppose I could just measure the width of the start bit & calculate
the appropriate baud rate.  But this will not work when changing the
baud rate without powering the device do.

Any ideas would be greatly appreciated.  Or better still a pointer to
any exising code if someone has any?

TIA
Maurice

1996\10\15@091014 by mfahrion

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face
> Hi,
>
> Does anyone have any ideas for implementing auto baud rate detection
> on the PIC16C73.  I don't want any switches hanging off my device and
> would like it to detect the baud rate anything between 1200 and 57600.
>
> I suppose I could just measure the width of the start bit & calculate
> the appropriate baud rate.  But this will not work when changing the
> baud rate without powering the device do.
>

This is easily done if you know what your first byte of data will
look like.  For example, if you can force the first byte of all
strings to be odd, you can simply measure the start bit width to
determine your bit widths.  Recalculate bit width at the beginning of
each string - this allows some other cost saving measures as well.
If you don't know anything about your incoming data, things will be
much more difficult.

Good luck
-mike
spam_OUTmfahrionTakeThisOuTspambb-elec.com
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Mike Fahrion                .....mfahrionKILLspamspam@spam@bb-elec.com      http://www.bb-elec.com/
B&B Electronics Mfg Co      ph.(815) 433-5100 ext.215    fax (815) 434-7094
707 Dayton Road                 PO Box 1040                  Ottawa IL 61350
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1996\10\15@100426 by Wireless Scientific

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At 4:17 AM 10/15/96, Mike Fahrion wrote:
>If you don't know anything about your incoming data, things will be
>much more difficult.


That's why modems require the "at" characters. Several modems, that I've
had the pleasure of dealing with, during the command mode handle the "at"
characters a little differently than the rest. During the autobaud mode the
rx and tx lines are tied together while the modem does a little
computation. After which the modem goes into a half duplex conversation and
echoes the characters after you've sent the last stop bit.

Why does this matter? If you are writing bit banging serial code and are
looking for an accurate echo of characters you send out, you will not see
the "at" chars come back because their reply bits are sent while you are
sending yours.

This is a gotch ya to look out for and has nothing really to with PICs.

craig




________________________________________________________
Dr. Craig Hollabaugh
Wireless Scientific, Inc.
1890 South 14th Street
Building 100, Suite 105
Amelia Island, FL 32034
904 261 6977
904 261 2129 fax
wscispamKILLspamnet-magic.net

Or you might know me as
Dr. Craig Hollabaugh
Analog Microelectronics, Georgia Institute of Technology
.....hollaKILLspamspam.....monique.adgrp.gatech.edu

or

Dr. Craig Hollabaugh
Aerospace Department, University of Texas, Austin
EraseMEhollaspam_OUTspamTakeThisOuTcfdlab.ae.utexas.edu

1996\10\16@073256 by Pedro Machado

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Hi,

I've seen auto baud rate detection in 'smart' rs232 Y cables, that let you
connect  a barcode reader to a rs232 connection between a terminal and a
host.
You put the Y cable in autodetect mode and then type UTUT at the terminal
prompt. If you notice U is 0x55 and T 0x54 in ASCII. So an U is a sequence
of low-high with bit duration. I presume thr microcontroller in the cable
counts the duration of the low-highs and then sets the correct baud rate.

Well this system isn't truly automatic, since you need to put it into
autodetect mode, but it's the closest thing I've seen.

Pedro Machado
pedromspamspam_OUTburotica.pt
----------
From: owner-piclist
To: Multiple recipients of list PICLIST
Subject: Auto bauding
Date: Tue, 96 de 10 de 15 10:39

Hi,

Does anyone have any ideas for implementing auto baud rate detection
on the PIC16C73.  I don't want any switches hanging off my device and
would like it to detect the baud rate anything between 1200 and 57600.

I suppose I could just measure the width of the start bit & calculate
the appropriate baud rate.  But this will not work when changing the
baud rate without powering the device do.

Any ideas would be greatly appreciated.  Or better still a pointer to
any exising code if someone has any?

TIA
Maurice

1996\10\16@080823 by Tony Grimer
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picon face
At 12:09 PM 16/10/96 G, you wrote:
many versions of Auto bauding have been used over the years..

in all cases a sequence is required that is unique enough to identify the
bit durations quickly and effectively. The old saga of the 1.5 bit stop can
cause a problem.

As has been point out 'U' is in ASC hex format 0x55 and alternating this
with the code hex 0xAA all the bits change state so the software problem is
not as great.

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Tony Grimer ----  @spam@cm1918KILLspamspamscitsc.wlv.ac.uk (Tony D. Grimer)

School of Computing (SCIT)  Room MU406 Tel - 0902-321810.

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