# S7-1200 multiple ISO-on-TCP connections



## Tim Kamrath (24 August 2010)

I have written my own dll (wrapping parts of libnodave) to communicate with a 1214 S7-1200 PLC via the builtin ethernet port. It is working fine for a single instance of my .net C# program, and I have it working on a PC and on a CE panel device. But what is not working is multiple connections. So when I run one instance the connection is successfull. When I start the second instance I cannot get a connection. Then when I kill the first instance the second instance gets connected. I think the problem has something to do with the ISO packet. My question is what is the location of the parameter in the ISO packet for changing this mode in the 1200?

There is parameter in the ISO packet that tells the 1200 what connection mode to use. In the libnodave _daveConnectPLCTCP function the packet data is somewhat documented for the CP243 communications, and this parameter is there. But I don't know where this parameter is in the regular TCP ISO packet. I think the default for this parameter is 1 (PG) and I need to change it to 2 (OP) so that the 1200 will support up to 3 connections. Can anyone tell me where this parameter is in the TCP ISO packet data block so I can change it?


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## Jochen Kühner (24 August 2010)

When you download my Version of libnodave, i've documented it in my version!

You can get it here:

http://jochensserver.dyndns.org/wordpress/?page_id=55

Maybe you can also share your source with us? (You know libnodave is under LGPL!)


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