> In such a system is a token managing node usually employed or is each node
given
> an address to pass the token to when its done? I'm wondering how hard its
going
> to be to add new nodes later.

For what it's worth, here is how I dealt with a RS-485 system where nodes
needed to be hot swappable:

Each node on the bus had a separate address.  Node 0 was the bus master and
was always present.  Nodes 1-N were slaves.  The master kept a list of
active nodes on the bus and gave each one a chance to talk in circular
fashion as fast as the bus bandwidth allowed.  If a node failed to respond
to three times in a row, the master crossed it off the list and the node
would not receive further requests to send.  Every once in a while, the
master would ping one of the addresses that it currently thought was
inactive.  If it got a response, that node would be added to the active
list.

This particular system used 4 bit node addresses, so there could only be a
maximum of 15 slave nodes.  The master pinged an inactive address once every
100mS, and the response timeout was 3mS so only about 3% of the bandwidth
was used to find newly active nodes and a new node would be discovered
within 1.6 seconds.  The system worked very well and nodes were indeed hot
swappable.  Newer versions of this system will probably use CAN because both
the 15 maximum slave nodes and the 115.2K bits/second will probably become
limitations as more things are asked from this bus than originally intended.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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