RSLinx OPC Server


Thread Starter


My customer is using RSLinx OPC Server with a .NET developed client. We are sending unsolicited message data from a ControlLogix PLC with a "connected" and "cached" MSG Instruction. There are actually multiple PLCs connected and several unsolicited MSG instructions used in each PLC.

On a very intermittent basis and only on certain MSG instructions, the PLC successfully sends the data (.DN bit is set for the MSG Instruction); but the OPC Server does not seem to fire the DataChange event in the client application. Most of the time the PC application gets the DataChange event.

On an Ethernet trace, we can see that in these few cases, the data made it successfully from the PLC to the PC's I.P. address with no CIP errors, at least as far as we can tell (we are not trace analysis experts!). We also know that the data is changing because there is an incremented message number value within the data being sent. The result is that the PLC is telling the PC of the arrival of a product at a pick up point where the client app is instructing a machine to pick it up. Machine sits idle because the PC application did not see the arrival event.

Does anyone have an idea as to what to look for in next RSLinx and/or O.S. (Windows server 2008) to see why a DataChange event will not fire?

curt wuollet

Ah, the wonders of shrink wrap software. Once it goes under the covers, you may need Rockwell or Microsoft assistance to figure it out. You probably want to start pinging them asap.


bob peterson

I am not sure that the DN bit actually means the message was successful. IIRC, for ethernet in an AB it only means the message was transmitted. It may not have been received.

Hmm, not sure if this is the answer, but make sure they are using the right OPC driver for the RSLinx conection. I've had problems like this before. There's a couple of options and the names can be misleading. Sorry I don't have access to an AB configuration just now so can't check the details for you.