User guide

Communication Capabiliites
890 USE 108 00 August 2001 95
Destination
Device
Requirements
The structure of the Modbus Plus routing address is determined by the type of
device at the destination node:
If you are initiating a transaction with another 984 controller, the last (rightmost)
nonzero byte in the routing scheme is the destination node address
If you are initiating a transaction with a network adapter in a non-controller node-
e.g., an SA85-the next to the last nonzero byte is the destination node address,
and the last nonzero byte is the task # (range: 1 ... 8)
If you are initiating a transaction with a single slave on a Bridge MUX port, the
next to the last nonzero byte is the Bridge MUX node address, and the last
nonzero byte is the desired MUX port # (range: 1 ... 4)
If you are initiating a transaction with a slave device on a Modbus network
connected to a Bridge MUX, the second from the last nonzero byte is the node
address of the MUX, the next to the last nonzero byte is the desired MUX port #
(range: 1 ... 4), and the last nonzero byte is the desired Modbus slave address
(range: 1 ... 247)
Any leading nonzero bytes ahead of the address bytes described above are
Bridge Plus node addresses.
Assume, for example, that your routing path is to a controller two networks
removed from the originating 984. The message is routed first to a BP85 Bridge
Plus at node address 25. The bridge forwards the message to node 20, a BP85
Bridge Plus device on the second network. Node 20 forwards the message to the
destination controller node address 12 on the third network. The zero-content
bytes in the fourth and fifth routing bytes specify that no further routing is required
beyond the third byte:
The following figure shows an example of a message frame routing path.
Modbus Plus Message Frame
Start
Routing
Bytes
End
PLC NODE 12
25 20 12 0 0
Routing Address 1
Routing Address 2
Routing Address 3
Routing Address 4
Routing Address 5