Thread Starter


We use 1756-DHRIO for ethernet communication between controller. In module properties, there is module fault: "(code 16#ff00) Connection Request Error: No connection instance". What is it mean?!

Michael E. Crossman

The 1756-DHRIO module is not for Ethernet communications. This module is only for DH+ or RIO communications.

If you would like to communicate Ethernet with a ControlLogix PLC you need the 1756-ENBT module.

Best regards,

Michael E. Crossman
PLCs Plus International, Inc.

Trevor Ousey \(lists\)

I assume you have the DHRIO for Data Highway Plus, installed on a ControlLogix processor. If you have both cannel A and B as DH+, and have the 1756-DHRIO module in the IO tree of your project, you will get this fault. It means nothing really. I would suggest removing it from the IO tree if you do not have Remote IO used, and if you are using an MSG instruction follow the standard CIP path structure.

For example, DHRIO is in slot 5 and a SLC5 is at Node 3, you would enter
1,5,2,3 as the path.
1 = backplane,
5 = DHRIO slot number,
2 = Ch A on DHRIO (3 is for ch.B)
3 = Node 3 (SLC5)


Trevor Ousey
BJH Controls P/L
Mt. Gambier, South Australia.