Tag engine to opc server communication protocol

When the tag engine talks direct to a plc with modbus rtu, there is a CRC checksum built into the communication protocol to provide reliable data transfer. When the tag engine talks directly to an opc server program, what protocol is used?? Is there any kind of checksum to verify data integrity??

OPC Client to OPC Server communication protocol is based on Microsofts DCOM architecture, which is an object model oriented communication mechanism based on RPC (TCP/IP). I as know, there is no checksum verification specifically as known in PLC protocols. However, there are some mechanism to support fault tolerance better. (see DCOM Technical Overview, section, Fault Tolerance)
You could find more info from Microsofts MSDN library e.g. Serach from MS MSDN Library on "DCOM", or DCOM Overview.
The OPC specification could be downloaded from the ion.org>OPC Foundation, specifically you could find a white paper on OPC, DCOM and Security as pdf file.
Hope this helps
Roland
PS: If someone needs more info on Modbus specification you might find it on Modbus.org

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Good day,
Try following the instructions on the driver’s help, take a look at the attach picture. It should be a good starting point. After the PLC is configured you can use this tutorial (Connect LabVIEW to Any PLC Using OPC » http://www.ni.com/white-paper/7450/en/) for a guide on how to monitor the tags.
I hope this helps
Alejandro | Academic Program Engineer | National Instruments
Attachments:
OPC Server Help.JPG ‏237 KB

Use Data Socket vi's to write to a custom namespace OPC server.

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I'm still having the following problem:
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Attachments:
locate_fflv_in_labview82.jpg ‏214 KB
vi.lib.zip ‏391 KB
locate_fflv_in_labview71.jpg ‏193 KB

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PierreN,
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Go to Solution.

Hi,
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http://www.ni.com/white-paper/7450/en
Connect LabVIEW to Any PLC Using OPC (Webcast)
http://zone.ni.com/wv/app/doc/p/id/wv-263
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www.ni.com/mcm
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www.ni.com/biganalogdata
512-683-5444

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Attachments:
manual_writing_to_plc.png ‏298 KB

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Thanks for the reply Charris,
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When I try doing this with the simulator, I first create the I/O server before I can browse all the tags in "create bound variables". But this time when I go to the DSM, they are not listed under the I/O server. This is just an observation.
My real problem is that I use this piece of code found on the NI website to get a list of tags (URLs). This code works with the remote OPC server but not with the simulator.
I don't really understand the code. All I know is that if I input the name of the library and the name of the I/O server as well as the path to the PC, it brings back a list of URLs pointing to tags. Maybe there is something in this VI you can help with.
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Attachments:
Get Tag List.vi ‏38 KB

Tag engine to opc server communication protocol

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