Installation guide

190 Message Routing
890 USE 100 00
B .1 The Modbus Plus Message Routing Path
A single Modbus Plus network can have up to 64 addressable node
devices, with each device having a unique address of between 1 and 64.
Multiple networks can be joined through Bridge Plus devices. Devices
address each other across Bridge Plus devices by specifying routing
paths of five bytes, with each byte representing an address on the next
network. This routing method allows nodes in other networks to be
addressed up to four networks away from the originating node.
The routing path is imbedded in the Modbus Plus message frame as it
is sent from the originating node:
MESSAGE FRAME
ROUTING
PATH
ROUTING ADDRESS 1
ROUTING ADDRESS 2
ROUTING ADDRESS 3
ROUTING ADDRESS 4
ROUTING ADDRESS 5
MODBUS PLUS
EXAMPLE: ROUTING ADDRESS 1 = 25
ROUTING ADDRESS 2 = 20
ROUTING ADDRESS 3 = 12
ROUTING ADDRESSES 4 AND 5
ARE ZERO (NO FURTHER ROUTING)
START
END
Figure 73 Message Frame Routing Path Field
Figure 73 illustrates message routing to a programmable controller
through three networks that are joined by Bridge Plus nodes. Using
the routing addresses in the figure, the message will first be routed to
node 25, a Bridge Plus on the local network. That node forwards the
message on to the Bridge Plus at address 20 on the second network.
The second Bridge Plus forwards the message to its final destination,
node address 12 on the third network. The zero contents of bytes 4 and
5 specify that no further routing is needed.