CompactLogix 1769-l16er - (5370) Unconnected Comms Only?!

I have a customer trying to communicate with a CompactLogix 1769-L16ER using TAG READ and TAG WRITE commands.

We connect with the node - but never get a response to our READ TAG messages - the documentation says that this controller only supports unconnected messaging. Anyone have any experience with this?

Did Rockwell really put out a controller that specifically does not support connected messaging?

Any help is appreciated.

What are they trying to communicate with? Another PLC? What model?

The only two ways I know to communicate with different processors in the Logix architecture is to use produced/consumed tags or through explicit messaging utilizing CIP Data Table Read/Write modes.

Our system is a DCS that communicates using explicit tag reads and writes. It is the same mechanism that the Rockwell controllers use in the MSG instruction.

According to the documentation on this controller it says that you must uncheck the "connected" box when configuring a MSG command with this controller. I wanted to make sure I have this correct.

Can you point to the exact document you are reading that describes unconnected messaging to this specific model of controller ?

What DCS system are you running ?

Communications - does this compactlogix really only support unconnected messaging.

Page 128 of this document - or search for unconnected.
http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1769-um021_-en-p.pdf

DCS is a D/3.

Thanks for pointing to that document. Publication 1769-UM021 is the User Manual for the 1769-L1 family of CompactLogix controllers.

I have the 2012 version of that document, where that citation is on Page 126, and reads:

All CompactLogix 5370 controllers must use unconnected MSG
instructions. When you configure a message for a CompactLogix 5370
controller, make sure the Connected checkbox on the Message
Configuration dialog box is cleared.

Click to expand...

The comment is made in a section of Chapter 6 (Communicate Over Networks) that is specifically describing how to use the Raw Socket interface mechanism, which is generally used for communication with things like barcode readers and label printers.

The third paragraph in the Socket Interface section of Chapter 6 suggests that the Unconnected requirement is specific to the Socket Interface:

All CompactLogix 5370 controllers must use unconnected MSG instructions with socket interfaces.

Click to expand...

This specific User Manual does not include a step-by-step example of ordinary CIP Data Table Read/Write messages because those are covered in other user manuals like 1756-RM003, the General Instruction Set Reference.

Appendix B of the 1756-UM021 manual gives a little table of connection capacities for the controller, which includes both 256 CIP Connections and 256 CIP Unconnected Messages.

In summary: I think that the comment in Chapter 6 about unconnected MSG instructions refers only to MSG instructions used in the implementation of Socket Interface features.

I found a Knowledgebase document (ID# 539345) that described the error message you get when you leave the Connected checkbox selected when implementing a Socket Interface with a CIP Generic MSG, and it re-iterated that CIP Generic MSGs for Socket Interface need to be un-Connected.

I'm not certain about that conclusion, though. I don't have a 5370 series CompactLogix handy to test with.

I do know that there is an important difference in CIP Path syntax between the 5370 series CompactLogix and the bigger/older 1756 ControlLogix and 1769 CompactLogix.

The modular, chassis-based ControlLogix always had separate Ethernet modules. The CompactLogix implemented a "virtual backplane", so the CPU was considered to be at Slot 0 and the Ethernet daughtercard was in Slot 1.

When you directed a MSG instruction at a ControlLogix, the final "hop" of the CIP Path was "1, x", where x was the Slot number of the ControlLogix.

When you directed a MSG instruction at an older 1769 CompactLogix like the popular 1756-L32E, the final "hop" of the CIP Path was always "1, 0", because the CPU used virtual backplane Slot 0.

When you direct a MSG instruction at a modern 5370-series CompactLogix like the 1769-L16ER, the final "hop" of the CIP Path is "2, aaa.bbb.ccc.ddd", where the final element is the IP address of the CompactLogix. The additional "1, 0" hop is not necessary.

I tested this when I had a 1769-L18ER in my shop along with a 1756-L61 and 1756-ENBT. I found that I could successfully send messages with the IP address as the final target, or by adding the "1, 0" hop. That's been over a year ago, though, so my recollection could have been incorrect or I might have been using different firmware than you are.

So this might or might not be the problem with your NovaTech R/3 interface.

For multi-vendor interface troubleshooting, there's no substitute for getting down and dirty with Wireshark or other network analysis tools.

If you can use a mirror port or a network tap and get a *.PCAP file, I'm sure that NovaTech technical support, RA Technical Support, or this Forum might be able to get some additional information from it.

Above I mis-typed 1756 and 1769 several times. It's been too long so I can't ninja-edit. I blame jetlag.

1756 is the Bulletin Number for modular slot-based ControlLogix.

1769 is the Bulletin Number for CompactLogix, both the older 1769-L32E/L35E and the new 1769-L1/L2/L3 series that are also called the "5370" series controllers.