A-B 1783-ETAPK Embedded Switch Technology

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 controller slot for port A is configured to “0”, the message is forwarded to the ControlLogix controller in slot 0.

Receiving Local DH+ Messages on DH+ Because a local DH+ message 

has only enough address information to get the message to a target node on the same DH+ network, 

the 1756-DHRIO and 1756-DHRIOXT modules that receive this message cannot identify where to send the message. 

The 1756-DHRIO and 1756-DHRIOXT modules use the Controller Slot configuration parameter to send the message to the local controller. 

You must use RSLinx software to configure the controller slot. 

Some messages, called PCCC commands, are not sent to the controller slot. 

In this case, the 1756-DHRIO and 1756-DHRIOXT modules generate a response to the message. 

For a complete list of these messages, see Appendix B. 

Local DH+ messaging does not require a populated routing table. 

Local DH+ messaging does require a default (that is a properly emptied) or an applied (that is a properly populated and saved) routing table, 

and a default or applied controller slot for each channel configured for DH+. 

A modern control system is more than its name implies. It delivers the fast system performance, 

high capacity and optimized productivity that you need from a control system today.