Message between 2 PLC5/20 via dhrio bridge

[controlled]

I'm trying to use a message instruction to read the value from a PLC5/20 into another. I have searched the forum, but am getting more confused.

Each of the PLC's use Node 40 as the DH+ address. They are wired into a control logix gateway utilizing a dhrio card and a ENBT card. The network works great as it is (I can go online with both controllers, and I have factorytalk view reading data from both controllers.)

From what I have read, i believe i need to use multihop messaging, but when i try to enter the MSG parameters in RSlogix, it doesnt give me the multihop option.

Any help would be greatly appreciated.

 

[Ken Roach]

What you need to do is called "Remote DH+ Link Addressing". It's a very old Data Highway Plus internetworking technique.

First examine both PLC-5's and find out what the Link ID for each one's DH+ port is. Not the Node Number, the Link ID. This is like a "network number" that can be used to tell one DH+ network from another.

Next examine the Routing Table in the 1756-DHRIO (right click in RSWho and select "Module Configuration").

What you need to do is set up each PLC-5 and DHRIO channel that are physically connected together so that they have the same Link ID. The Link IDs for the two different DH+ networks need to be different.

Then when you send a MSG command you select "Remote" instead of Local, and enter the Target Link ID as well as the Target Address, and the address of the Gateway (the 1756-DHRIO port).

There is a pretty good example of how all this works in the 1756-DHRIO User Manual, publication 1756-UM514.