Rockwell Automation 1756-DHRIO_DHRIOXT ControlLogix Data Highway Plus-Remote I/O Communication Interface Module - Manual (Page 25)

Rockwell Automation Publication 1756-UM514C-EN-P - June 2014 25
Using the Data Highway Plus Network Chapter 2
Two Methods of
Communication Over a DH+
Network The 1756-DHRIO and 1756-DHRIOXT modules act as a bridge for two
methods of communication. These methods are:
• DH+ Messaging
• Control and Information Protocol (CIP) Messaging
The following table lists the devices that support each communication method.
Use DH+ Messaging DH+ Messaging offers the following benefits:
• You can send messages between devices on the same link.
• You can send messages between devices on different links.
• It is compatible with many Rockwell Automation® modules.
DH+ messaging is divided into two types:
• Local DH+ Messaging - See page 25
• Remote DH+ Messaging - See page 28
Before you can design a control system to meet your application needs, be aware
of the difference between Local DH+ Messaging and Remote DH+ Messaging.
Local DH+ Messaging
Devices use local DH+ messaging to communicate between devices on the same
physical link. A device that uses local DH+ messaging must:
• generate local DH+ packets.
• support local DH+ protocol.
• send and receive messages.
A local DH+ message sent on a DH+ network has only enough address
information to get the message to a target node on the same DH+ network.
The example in the following figure shows a PLC-5 controller sending a message
to port A on the 1756-DHRIO and 1756-DHRIOXT modules. Because the
Type of communication: Devices and Software supporting this type:
DH+ messaging PLC-3
PLC-5
PLC-5/250
SLC 500
ControlLogix controllers
RSLinx software
Interchange software
Control and Information Protocol
(CIP) messaging ControlLogix controller
Studio 5000 environment