Installation guide

Message Routing
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Programmable Controllers
For programmable controllers, the last nonzero byte in the message
routing specifies the network node address of the controller (1 to 64).
HostBased Network Adapters
For hostbased network adapters, the routing bytes specify the
network routing to the adapter’s node address. Then, any bytes
following the adapter’s own address can be used by the internally by
the adapter application program (for example, to route messages to
specific tasks within the application). Routing details are provided in
the guidebook for each hostbased device.
Bridge Multiplexers
For bridge multiplexers, the routing field contents are specific to the
type of device being addressed.
For a single slave device at a Modbus port, two bytes are used to
address the device. The nexttolast nonzero byte addresses the
multiplexer node (1 to 64). The last nonzero byte specifies the port (1
to 4), and therefore the single device.
For a networked Modbus slave device, three bytes are used to address
the device. The third byte from the last nonzero byte addresses the
multiplexer node (1 to 64). The nexttolast nonzero byte specifies
the Modbus port (1 to 4). The last nonzero byte specifies the Modbus
address of the slave device (1 to 247).