Installation guide

Introducing the Modbus Plus Network
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1.6 How Nodes Access the Network
1.6.1 How Your Application’ s Layout Affects Node Access
When the network is initialized, each node becomes aware of the other
active nodes. Each node builds a table identifying the other nodes.
Initial ownership of the token is established, and a token rotation
sequence begins. Your choice between laying out your application as
one large network, or as several smaller networks, affects the timing of
the complete token rotation.
For example, tokens are not passed through Bridge Plus nodes,
although messages can be addressed through Bridge Plus nodes to
destination nodes. You can therefore construct your networking
application as several smaller networks, joined by Bridge Plus nodes.
The fast token rotation time in each small network allows rapid
transfer of high-priority data, with lower-priority data passing through
bridges to other networks. This facilitates time-critical messaging to
nodes that are tightly linked in an application.
1.6.2 The Token Rotation Sequence
The token sequence is determined by the node addresses. Token
rotation begins at the network’s lowestaddressed active node,
proceeding consecutively through each higheraddressed node, until
the highestaddressed active node receives the token. That node then
passes the token to the lowest one to begin a new rotation.
If a node leaves the network, a new tokenpassing sequence will be
established to bypass it, typically within 100 milliseconds. If a new
node joins, it will be included in the address sequence, typically within
5 seconds (worst-case time is 15 seconds). The process of deleting and
adding nodes is transparent to the user application.
Where multiple networks are joined by bridges, tokens are not passed
through a bridge device from one network to another. Each network
performs its token passing process independently of the other
networks.