Instruction Manual

Rockwell Automation Publication 1756-UM514C-EN-P - June 2014 27
Using the Data Highway Plus Network Chapter 2
Sending Local DH+ Messages on DH+
If a 1756-DHRIO channel receives a DH+ message with a destination link ID=0
from a ControlLogix controller in the same chassis, the module sends the
message as a local DH+ message.
Limitations of Local DH+ Messaging
When using Local DH+ Messaging, you must remember:
• The DH+ message contains only a node ID for a node on the DH+
network.
• A local DH+ message sent to the node ID of a port on the 1756-DHRIO
and 1756-DHRIOXT modules is forwarded to one user-configured
controller slot.
• Messages on one DH+ network cannot be routed to other networks.
Routing Error in Local DH+ Messaging
If the module has a problem with routing a DH+ message, it can return a
response with an error status of D0 hex. A PLC-5 displays this error as D000 hex
when monitoring the message instruction. If you receive this error message,
perform the following actions:
• Check your message instruction to make sure a destination node was
entered.
• Check your default slot configuration to make sure that it matches the
location of the ControlLogix controller in the chassis.
• Make sure power is applied to the module.
Programming Message Block Instructions in a Controller for Local DH+ Messaging
Before programming your message block instructions in your controller, you
must:
• Determine which links send and receive DH+ Local messages.
• Draw a network to make sure you meet the design requirements for Local
DH+ messages.
IMPORTANT
The target of the DH+ message must be on the same DH+ link as the 1756-
DHRIO and 1756-DHRIOXT modules sending the message. Also, the
ControlLogix controller must reside in the same chassis as the 1756-DHRIO
and 1756-DHRIOXT modules sending the message on DH+.