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I'm trying to interface .NET (C# or VB doesn't matter) with a Siemens PLC S7 200. I can't however get a connection set up. I'm working on a Win7 64bit machine but can't seem to get it working on 32bit either. I got two files:

Interop.OPCSiemensDAAutomation.dll Siemens_s7-200.dll

From another project which I'm trying to migrate to a newer system. However I get a com exception all the time.

Retrieving the COM class factory for component with CLSID {01704EBD-44B5-11D3-9C09-00105A3DD3AC} failed due to the following error: 80040154.

I've already tried libnodave and can't seem to get that working either. Can somebody provide me with some pointers (please no XKCD humor on that one) to where to look?

I couldn't get Siemens PC-Access to install on this machine, will try on a WinXP 32bit later. I read something about I need an OPC server or something on the machine?

Please bear with me, first time interfacing with a PLC :/

Henrik
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  • Sorry I forgot to say that it's over a USB PPI cable to the PLC itself. I have also already tried to register the two DLL's i listed above using regsvr32. – Henrik Jul 25 '11 at 15:36
  • Are you trying to get at the data values in the PLC? Read/Write type stuff? – jwatts1980 Jul 25 '11 at 16:38
  • @jwatts1980 Exactly! I only need to interact with 3 values. I don't know why it can be so hard... Makes me wanna rip out the guts of that thing and stuff in an Arduino :P By the way, will be sure to post it when / if I find a solution. – Henrik Jul 25 '11 at 18:35
  • I HAVE NEW INFORMATION! Turns out my client wants me to use Simenens PC Access software. It includes Simatic OPC Server. And that system is actually creating a virtual COM port for me to access so I don't have to go through OPC myself or access the PLC. Next problem is how the **** (sorry for my expression, i'm getting tired of this) to talk with the plc over COM. I can easily connect to the COM port and such, but I can't get a response from the PLC. My guess is that they have some special programming behind it. There is only one way to find out, I will be sure to report back my findings. – Henrik Jul 27 '11 at 02:57

3 Answers3

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The COM exception is a fairly generic error that indicates that the COM library itself or one its dependencies could not be loaded. Some things I would check are:

  • Is the COM library registered on the machine? You can use regsvr32 to register a COM dll.
  • Does the COM library require other dependencies that may not be on the machine? You can use dumpbin /dependents to figure this out.
  • Does the Siemens PC-Access software have to be installed on the machine? You said that you could not get it to install which probably explains why the COM library could not be loaded.

Unfortunately this about all the help I can provide in solving your specific problem. However, I can point out that you can use the following products which act as OPC servers and have drivers that are compatible with the Siemens S7. These would be alternatives to using the Siemens OPC server.

I have used both products in the past and I am pretty sure I used one of them (I cannot remember which one) to talk to a Siemens S7.

Also here is a really good website with information about using OPC in .NET.

Brian Gideon
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  • Thanks for the reply! I actually got PC-Access up and running on a 32bit machine with XP (in a VM) so it's probably that. But the problem is now that it's an evaluation version and that is a no go. Their previos software used some free library (I can't guess what as it's just dll's) or something like that, and also it gets problematic to deploy a whole solution like PC-Acccess. So will definitly check out your links. – Henrik Jul 25 '11 at 16:34
  • I'll ditto the Kepware link. Kepware server itself is free... you pay for the drivers to connect to certain PLCs. Not sure if Kepware has any .NET APIs of any kind. – jwatts1980 Jul 25 '11 at 16:53
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I've looked into doing this type of thing before. If you try to get at the controller directly, you could run into all kinds of proprietary issues. Automation software companies tend to keep a very tight reign over their protocols. If it's only the data you're after, then OPC is probably the best way to go. However, from what I've found, that's not free either. The OPC Foundation (opcfoundation.org) has a .NET API that's available at a cost in the $1-2K range I believe.

jwatts1980
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  • Hmmm I really wonder how their previous solution worked. I will try and analyze it in depth, but I can only seem to find those DLL's. Sometimes I wish that such simple device as the one I'm developing against would just use a standard serial port. – Henrik Jul 25 '11 at 17:15
  • @Henrik: If you happen to get this problem solved, and think about it, could you post an overview of your solution here? I'd love to know what ended up working for you... thanks! – jwatts1980 Jul 25 '11 at 18:27
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Try again. I have successfully used libnodave with S7 200, 300 and even 400 and 400H (redundant ones). No experience with C#, but it is working 24/7 (steelshop and blast furnace) in my linux C daemons and in Delphi and Lazarus Windows applications. If you can't make it, then prepare to spend $$$$ on OPC server for S7 200 (Kepware, Matrikon...) and for OPC client library in C#.

avra
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