//Tested with:   (S7-1500 V2.8; S7-1200 V4.4)

PLC CPU 1518-4 PN/DP MFP and TIA Portal V17.

Is there some standard function block like LOpenUserComm wich can send (TSEND) and receive (TRCV) in one cycle?

Thanks in advance.

Dear Dennis Dutchman,

already the instructions TSEND/TRCV itself work asynchronously, therefore there are also no other blocks/program examples working in one cycle.

What do you want to achive exactly? Do you want to transfer data to another cpu?

Maybe there are other communication methods then OUC you can use as an alternative (like I-device).

regards

sancruz

Hi Stefan,

thanks for your reply.

I have a socket communication with AS400 as partner.

Wenn I send an (generated by PLC) ACK message of a received telegramm, most of the time I don't receive the next message. It seems that in State sending receive doesn't work, when state sending changes to idle the before received message is not detected.

I did not read yet the documentación of the LCom library, but don't know if it's compatible with  the AS400 dirver.

Stefan Arcularius

Hi Dennis Dutchman,

I am not sure how to understand your question. Because with "LOpenUserComm" you are able to receive during sending. But it would never be possible, to receive the response on the just sent message within the same PLC cycle.

If you are only asking because of using TIA V17 while the library is only provided as V15 or V16 than the solution might be an update which would be done when opening the library in V17. Or, as a recommended alternative, you can just use LCom.

Kind regards
Stefan

 The LopenUserComm function has a state machine which take multiple OB1 cycles to achieve sends and receives. Messages are missed and buffers get full when trying to adapt programs which worked in Step7 for S7-300 and S7-400 CPUs....
I think this is the reason for the question ?

Hello,

I had the same issue(s), maybe this will help someone.

If you want to use the templates provided by Siemens, there seem to be multiple function blocks for TCP-based Open User Communication published by Siemens.

This is the one Dennis Dutchman mentioned:

https://support.industry.siemens.com/cs/de/en/view/109747710

From my understanding the function block in this library has separate states for receiving and sending, so receiving and sending is processed sequentially.

I also had the problem that sometimes I would lose telegrams. So I had to adjust the state machine. The problem I saw with this version is, that outside of the state machine (CASE statement) the "send request" will just force the state machine from any state into the "Sending" State, so it could theoretically occur that a "New Data Received" is lost.   

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Alternative 1:

I would personally recommend using LCom from this library as it is more advanced, still gets updated and has more functionalities (e.g. more diagnostics, advanced protocol etc.)

https://support.industry.siemens.com/cs/de/en/view/109780503

Alternative 2:

You can also find a Master copy in this library called "TcpTemplate". Here it was actually realized in a way that receiving and sending is processed simultaneously, it is even mentioned in a comment in the code, but I have not tested it myself yet. 

Good Luck!