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How to communicate via Ethernet between PLCs Siemens S7-400H (redundant) and a PC with Linux OS?
The PLCs are redundant.
The PC is not a SCADA, it's a Level 2 computer.
What communication protocols can be used?
Which protocol is recommended?

What I have seen is Profibus. No idea where they got drivers, etc. Probably pretty spendy. I considered such a hookup and the Profibus card would have cost more than the rest of the system. They do have something that can run on an ethernet lan but I haven't seen anything third party for that.

Regards

cww

I am not familiar with the S7-400H redundant, so I don't know if there is something special about it which limits its ability to use various communications methods. One obvious question is how to handle the redundancy.

I can give you some suggestions about what to look at, but I think you will need to talk to Siemens about what their hardware is capable of.

1) Have a look at libnodave. http://libnodave.sourceforge.net/index.php

2) I believe that some people have also done raw socket communication with Siemens PLCs. I don't know any details of that though.

3) There are also Ethernet modules that can plug into the S7 rack which allow the use of more normal protocols such as SMTP, HTTP, SNMP, and FTP. They also support a large number of proprietary Siemens protocols. Not all of these may work on a 400H though. Have a look on the Siemens web site for information on the S7 443 modules. Siemens usually has all their manuals available for download as PDFs.