Yaskawa VS-616G5 Modbus Plus Communication Card - Manual (Page 7)

Introducing the Modbus Plus Network 1-3
How the Network Operates
Network nodes are identified by addresses assigned by the system designer. Each device is
independent and its node address is unique. Duplicate node addresses are not allowed.
Addresses are within a range of 1 to 64, and are not required to be sequential.
How Nodes Access the Network
Network nodes function as peer members of a logical ring, gaining access to the network
upon receipt of a token.
Initialization:
When a network is initialized, each node becomes aware of the other
active nodes. Each node builds a table identifying the other nodes, and initial ownership
of the token is established.
Token Hold:
While holding the token, a node initiates message transactions with other
nodes. Each message contains routing fields defining its source and destination on the
network.
Token Pass:
While passing the token, a node can write into a global database, for
broadcast to all nodes on the network. Other nodes monitor the token pass and can
extract the global data if programmed to do so.
Token Rotation Sequence
The token rotation sequence is established by node address. 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. This rotation
occurs without respect to the physical proximity of one node to another.
If a node leaves the network, a new token passing sequence is established, typically
within 100 milliseconds. New nodes joining the network are included in the correct
address sequence for passing the token, typically within 5 seconds.
When 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 other networks.