Allen-Bradley ControlLogix 1756-DH485, User Manual, Page: 48 / 110

Publication 1756-UM532A-EN-P - May 2006
4-2 Use RSLinx Software to Create a Routing Table
Use RSLinx Software to
Create a Routing Table
DH-485 protocols do not use the Common Industrial Protocol (CIP), the
communication protocol used in the ControlLogix architecture. The
1756-DH485 module is the transition point from the DH-485 network to
ControlLogix. In this capacity, the 1756-DH485 module serves as the DH-485
message source and requires a full message route, or path, to deliver the
message. A routing table, using link IDs and node addresses, provides the full
path.
What Is a Routing Table?
Before you can create a routing table for your 1756-DH485 module, you must
assign link IDs to all networks (including ENET and CNET) that route
information through the module. Link IDs are numbers from 1 to 199.
DH-485 module addressing provides the link IDs and node addresses. The
routing table translates link IDs and node address information into path, or
routing, information. Thus, the routing table specifies a 'map' to other links in
the system. Routing tables are set up at each node to build accurate
connections.
ControlLogix Routing
The ControlLogix routing protocols use CIP, a message-based protocol that
implements a relative path to send a message from the source device in a
system to the destination device. In this way, the source device in a networks
system contains the path information that steers the message along the proper
route to reach its destination. Since the source device holds this information,
other devices along the path simply pass this information; they do not need to
store
it. ControlLogix routing has two significant benefits:
•
You do not need to configure routing tables in the bridging module,
greatly simplifying maintenance and module replacement.
•
You maintain full control over the route taken by each message, enabling
you to select alternative paths for the same end device.