I generally implement a hardware solution that uses the RS-232 ports to both
read and write at the same time for RS-485 products in a CSMA/CD
arrangement.

The software does the heavy lifting by checking if a sent message has a) a
bit corrupted, b) a byte corrupted or c) a checksum sent wrong (all by
employing a task to read my own outgoing message.) On the incoming, either
anomalies in the received message (illogical length, etc.) or bad checksum
will trigger a collision detection / corrupted signal. Then the program
falls into Ethernet mode and jams the line for a while to warn everyone that
something bad has happened. Then the sending station waits a random amount
of time (that's the collision avoidance part) before resending.

The code always varies depending upon the application, hardware, language,
etc. Haven't had much luck with token passing schemes.

Tom

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Wollenberg, Frank
> Sent: Wednesday, August 22, 2001 07:10 AM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC]:Thoughts on RS485 collision detection
>
>
> On Sunday, July 22, 2001 10:24 PM, Douglas Wood
> [mailto:dbwood@KC.RR.COM]
> wrote
> >
> > I have a curcuit that utilitizes a full-duplex, multi-drop
> > 485 network with
> > collision detection/avoidance. I could forawrd you a copy if
> > you'd like...
> >
> What solution do you have, hardware or software ?
> BTW i'm interested in how do  you solve the problem "collision
> detection/avoidance".
> Frank
> ----------------------------
> GSP Sprachtechnologie GmbH
> Frank Wollenberg
> HW-Entwicklung
> Tel.:   +49 (0)30 769929-78
> Fax:    +49 (0)30 769929-12
> eMail:  f.wollenberg@gsp-berlin.de
>
>
> --
> GSP Sprachtechnologie GmbH
> Teltowkanalstr.1, D-12247 Berlin
> Tel.:  +49 (0)30 769929-0
> Fax:   +49 (0)30 769929-12
> eMail: Info@gsp-berlin.de
> Web:   http://www.gsp-berlin.de
>
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways.  See http://www.piclist.com/#archives for details.
>
>

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.