RE: Re: RS485 - XPL on the wire

["Ian Lowe" <ian@xxxxxxxxxxxxxxxxxx>]

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

No...

You would use an RS485 driver chip as before, so connect from the USART
on the PIC to the serial port on the 485 Driver, then the A/B wires of
the RS485 bus run from node to node.

The "ring" is logical, rather than physical.

So, each node on the network was an ID number settable via jumpers - the
token is "passed" by the master device (just software) to the
first
address, which sends anything it needs to, then "passes" the
token on...
The next device gets the token, broadcasts if it needs to, then passes
it on. And so on..

Each time a device sends the token, it's actually broadcast to everyone
on the shared bus, so the token contains an address for the previous
node.

It might be better (in fact, I think it would be *much* better) if the
token passed from a node back to the master each time.. And the master
keeps a note of which node is "next"...

I'll see if I can knock up a wee diagram for this, as it can get very
complex very quickly!!

Ian.


> 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
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> > >
> > >
> > >
> > >
> > >
> >
> >
> >
> >
> > xPL Links: http://www.xplproject.org.uk http://www.xplhal.com
> > http://www.xpl.myby.co.uk
> > To Post a Message: ukha_xpl@xxxxxxx
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> >
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> >
> > xPL Links: http://www.xplproject.org.uk http://www.xplhal.com
> http://www.xpl.myby.co.uk
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