Schneider Electric 174 CEV - Manual (Page 37)

Configuring the Bridge
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3.5.2 Destination Indexes 0 and 254: Dynamic Message Routing
The bridge provides a means for dynamic routing of messages at runtime.
Dynamic routing applies only to messages initiated from TCP/IP hosts, and
requires the host to configure the bridge at runtime (to Destination Index 255).
You should be aware of your options for using dynamic routing in your application,
as you setup your mapped routings. Two Destination Indexes are reserved for
routing messages dynamically: 0 and 254 decimal. Your options are:
H Destination Index 0: Host--based routing A Modbus Plus routing path is
available in the bridge at index location 0 for runtime use by TCP/IP hosts.
When the host configures a path in the bridge, any message from that host
addressed to index 0 will be routed to that Modbus Plus path. The bridge
maintains a cache of up to 10 associations between TCP/IP hosts and
Modbus Plus paths.
This routing option allows the bridge to be configured for simple addressing
to Modbus Plus from TCP/IP nodes which do not support gateway routing.
H Destination Index 254: Socket--based routing A Modbus Plus routing
path is available in the bridge at index location 254 for the current TCP/IP
host connection only. The bridge maintains one socket connection at that
index location for each of its eight Program and eight Data paths.
This routing option allows the bridge to handle concurrent sessions from one
TCP/IP host, or from multiple hosts, using independent routing assignments.
It provides flexibility for your application to manage routing dynamically, in
addition to the bridge’s fixed mapping table.
Section 3.9 provides examples of dynamic routing.
3.5.3 Destination Index 255: Bridge Internal Command
Messages received by the bridge addressed to Destination Index 255 cause the
bridge to execute an internal operation. This index is used to configure the bridge
for dynamic routing, or to invoke an upload or download operation between the
host and bridge.
Section 3.9 provides examples of dynamic routing. Sections 5.2 and 5.3 provide
examples of uploading and downloading.
3.5.4 Reserved Destination Indexes
Destination Indexes 250 ... 253 are reserved and are not available for use.