Hi experts!

TIA V14 SP1

PLC: 1214C DC/DC/DC or 1512SP-1 PN as the client of the TCP-connection

PC with a custom program as the server of the TCP-connection

I've been programming and improving a communication FB for some time now and am at the point where it (almost) does exactly what I want it to do.

It all works fine if I connect to the server and start sending and receiving my messages.

Once I disconnect and reconnect though (either by unplugging the LAN-cable or by using TDISCON), the FIRST message the server should respond with never gets sent.

This at fist looked like a server-problem, but after a few trial runs with Hercules, I figured out that only if the previous client was the PLC, the next connection has this fault.

If I connect and disconnect with Hercules and connect with the PLC afterwards, all's well.

I tried the whole thing outside of my FB with only a TCON, TDISCON, TDIAG, TSEND and TRCV...

same issue

So I was wondering...

Does the TDISCON send any "S***w you guys, I'g going home" message to the server upon disconnecting, or does it simply cut the connection on the PLC's side and be done with it?

Have any of you encountered a similar error?

Thanks in advance for your help!

Greetings, Mike

P.S. I aslo tried storing the connection data in a global system DB TCON_IP_V4 or a local TCON_IP_V4 -> no difference

Hello,

some days ago, I sniffer with wireshark, because I also wanted to know what is send with TDISCON.

I find out, that S7-300 send a "FIN" -Flag ("Final") and S7-1200/1500 a "RST"-Flag ("Reset").

In my case, I had a PC Programm (.net application) which do not recognize, that S7-300 disconnect the connection. The pc porgramm only react if S7-1200 sends a disconnect.Means: the PC program only recognize the "RST"-Flag- not the "FIN".

Perhaps this information helps you.

Thanks to Pittiplatsch and Duris_I!

I'll forward it to the programmer of the server-program and suggest that he listens for both flags and terminates the connection upon receiving them.

This solution looks pretty promising from what I can discern!

P.S. does someone of you know wheather I can make TDISCON send a "FIN" instead of a "RST" by any chance?

Duris_I

Hello,

well, I recommend use 'clear' solution, mean use resourcies what you have as programmer of PLC available. In this case (also if other methods exists) you need use available instructions/blocks and use them as instructed for disconnect. This is simply life, firmware can dictate system of functionality. Basically (my opinion also with experience from other side of problem), as PC app programmer I know that I have more options to solve this problem as PLC programmer. My opinion and maybe recommendation.

 Seems like the best solution, yes.

I was hoping that there were solutions to keep my program as widely compatible as possible by using the standard disconnect option, but it seems that Siemens foiled my plan here

Thanks for your support, I'll carefully approach the programmer with this change