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Re: Re: RS485 - XPL on the wire




> If we adopt a master with multiple slaves model, then the master needs
> to poll the slaves regularly (with a nasty overhead!). If instead we
> adopt a token passing model...

True

> Then a "token" is passed from station to station. It's like
the safety
> key used when crossing single track railway bridges etc - if you don't
> hold the key, you can't talk.

So does that mean hardware wise  serial out of Node 1 goes to serial in of
node 2 ???? and so on ??

> You have a control system in place on the "master" device -
if a token
> hasn't been seen for a second or so, it will send a special message
> around that clears the ring and starts again...

Would this be a hardware device or software app ??

Frank

----- Original Message -----
From: "Ian Lowe" <ian@xxxxxxx>
To: <ukha_xpl@xxxxxxx>
Sent: Friday, October 22, 2004 7:23 PM
Subject: RE: [ukha_xpl] Re: RS485 - XPL on the wire


>
> Well...
>
> In a peer to peer environment (like xPL) any device needs to be able
to
> send a message.
>
> If we adopt a master with multiple slaves model, then the master needs
> to poll the slaves regularly (with a nasty overhead!). If instead we
> adopt a token passing model...
>
> Then a "token" is passed from station to station. It's like
the safety
> key used when crossing single track railway bridges etc - if you don't
> hold the key, you can't talk.
>
> IBM built a very resilient network system called Token Ring which
> implemented this same mechanism.
>
> Using the shared access medium (the twisted pair network) we could
have
> multiple stations all able to send a message, with a token passing
from
> node to node giving them the right to speak...
>
> You have a control system in place on the "master" device -
if a token
> hasn't been seen for a second or so, it will send a special message
> around that clears the ring and starts again...
>
> Ian.
>
> -----Original Message-----
> From: Frank Mc Alinden [mailto:fmcalind@xxxxxxx]
> Sent: 22 October 2004 10:12
> To: ukha_xpl@xxxxxxx
> Subject: Re: [ukha_xpl] Re: RS485 - XPL on the wire
>
>
> Hi Ian
>
> > One station can talk, the others listen - easy enough, but how
can you
> > *tell* someone else is talking?
>
> AFAIK  you cant ......each node only responds to an Addressed message
> from a Master .....so thererfore not interested in whos talking ....or
> are you interested in whos talking ????
>
> Frank
>
>
> ----- Original Message -----
> From: "Ian Lowe" <ian@xxxxxxx>
> To: <ukha_xpl@xxxxxxx>
> Sent: Friday, October 22, 2004 7:05 PM
> Subject: RE: [ukha_xpl] Re: RS485 - XPL on the wire
>
>
> >
> > One of the biggest gotcha's for me was simply the technical
aspects of
> > RS485 on the wire...
> >
> > One station can talk, the others listen - easy enough, but how
can you
> > *tell* someone else is talking?
> > I guess I'm thinking in terms of a CSMA/CD situation like
ethernet and
> > couldn't find any RS485 chip that gave you Carrier feedback to
> indicate
> > that the media was in use.
> >
> > I guess you'd have to implement a token passing network system
like
> > token ring...
> >
> > Ian.
> >
> > -----Original Message-----
> > From: Frank Mc Alinden [mailto:fmcalind@xxxxxxx]
> > Sent: 22 October 2004 08:07
> > To: ukha_xpl@xxxxxxx
> > Subject: Re: [ukha_xpl] Re: RS485 - XPL on the wire
> >
> >
> > Hi Lehane / Ian
> >
> >             Like Ian  I am also interested in xpl 485 enabling
> > stuff...But to develope stuff we need to get more feedback from
xPL
> > Users on the sort of devices that they would like....Would be
nice if
> > several rs485 developements going on at the same time by
different
> > people.....I think there would need to be a RS232 / 485 convertor
made
> > which means one side would have to be bit banged , not aware of
any
> pics
> > with  2 uarts ??or a commercially available unit ??
.............Have
> > done a little bit on rs485 and used the chksum as you
> > decribed.............Im more than happy to get involved in
> > rs485 projects if  others are and there is enough interest as
> well......
> >
> > This link mentions the rs485 stuuf i was playing with
> > http://skybax.rapidhoster.co.uk/~armagh/page10.html
> >
> > Frank
> >
> >
> > ----- Original Message -----
> > From: "g8kmh" <lehane@xxxxxxx>
> > To: <ukha_xpl@xxxxxxx>
> > Sent: Friday, October 22, 2004 1:49 AM
> > Subject: [ukha_xpl] Re: RS485 - XPL on the wire
> >
> >
> > >
> > >
> > > OK,
> > > I'd missed xpl_devcom in my searches, oops!
> > >
> > > LRC-8 is a simple checksum on the message. XOR everything
after STX
> > > including ETX and the result is the checksum. No big deal to
do and
> > > offers some protection against message corruption, which
since the
> > > RS485 is going to be around mains cabling (even taking into
account
> > > normal separations) I think is a reasonable precaution.
> > >
> > > Be interested in the PIC implementations....
> > >
> > > Thanks,
> > > Lehane
> > >
> > > <snipped>
> > >
> > >
> > >
> > >
> > >
> > >
> > > xPL Links: http://www.xplproject.org.uk http://www.xplhal.com
> > http://www.xpl.myby.co.uk
> > > To Post a Message: ukha_xpl@xxxxxxx
> > > To Subscribe:  ukha_xpl-subscribe@xxxxxxx
> > > To Unsubscribe:  ukha_xpl-unsubscribe@xxxxxxx
> > > Yahoo! Groups Links
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> >
> >
> >
> >
> > xPL Links: http://www.xplproject.org.uk http://www.xplhal.com
> > http://www.xpl.myby.co.uk
> > To Post a Message: ukha_xpl@xxxxxxx
> > To Subscribe:  ukha_xpl-subscribe@xxxxxxx
> > To Unsubscribe:  ukha_xpl-unsubscribe@xxxxxxx
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > xPL Links: http://www.xplproject.org.uk http://www.xplhal.com
> http://www.xpl.myby.co.uk
> > To Post a Message: ukha_xpl@xxxxxxx
> > To Subscribe:  ukha_xpl-subscribe@xxxxxxx
> > To Unsubscribe:  ukha_xpl-unsubscribe@xxxxxxx
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
> >
> >
>
>
>
>
> xPL Links: http://www.xplproject.org.uk http://www.xplhal.com
> http://www.xpl.myby.co.uk
> To Post a Message: ukha_xpl@xxxxxxx
> To Subscribe:  ukha_xpl-subscribe@xxxxxxx
> To Unsubscribe:  ukha_xpl-unsubscribe@xxxxxxx
> Yahoo! Groups Links
>
>
>
>
>
>
>
>
>
>
>
>
> xPL Links: http://www.xplproject.org.uk http://www.xplhal.com
http://www.xpl.myby.co.uk
> To Post a Message: ukha_xpl@xxxxxxx
> To Subscribe:  ukha_xpl-subscribe@xxxxxxx
> To Unsubscribe:  ukha_xpl-unsubscribe@xxxxxxx
> Yahoo! Groups Links
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