Rockwell Automation 1756-DHRIO_DHRIOXT ControlLogix Data Highway Plus-Remote I/O Communication Interface Module - Manual (Page 29)

Rockwell Automation Publication 1756-UM514C-EN-P - June 2014 29
Using the Data Highway Plus Network Chapter 2
The following figure shows an example of remote DH+ messaging between PLC
processor A and PLC processor B. In this example, the following information
must be included in the remote DH+ message routing message instruction:
• local DH+ node = 020
• destination link ID = 2
• remote DH+ node = 030
Link IDs
To use remote DH+ messaging, each network that is an originating network or
target network requires a unique link ID. The modules require these link IDs to
be decimal values between 1-199. Each DH+ channel on a 1756-DHRIO or
1756-DHRIOXT module requires its own unique link ID.
The message originates on the source network. The destination network is the
message’s target network. This applies to all source and destination networks,
including DH+, ControlNet, Ethernet and a ControlLogix chassis.
Routing Tables in Remote DH+ Messaging
The modules contain a routing table that you define for your application. The
routing table contains information used to steer remote DH+ messages through
the system to ‘remote’ nodes on separate networks. By using the routing table, the
ControlLogix Chassis
1756-DHRIO and 1756-DHRIOXT Modules
PLC-5/25 Controller A - Node:010
Link ID 1
PLC-5 Controller B - Node: 030
41363
Link ID 2
Channel A - Node: 020
Channel B - Node: 025
IMPORTANT For remote DH+ messaging, the ControlLogix chassis is considered a
separate, independent network. Therefore, a system of 1 DH+ network and
one ControlLogix chassis is a two-link system.
The ControlLogix chassis is required to be a separate, independent link for
DH+ messaging if multiple message target ControlLogix controllers are in a
ControlLogix chassis.