S7 1500: tdiscon doesn't close the connection cleanly

EMTABAR

<snip>
It seems the connection resource is still occupied for more than 10 seconds after TDISCON is called despite TDISCON's "DONE" status flag being set straightaway.
</snip>

Hello.

Your finding is shocking yet not surprising. I am not aiming to defend Siemens' design choices on this topic. I only thought I should mention that what you found is documented. Please see the attached.

This design decision severely cripples the S7-1200 to have multiple communication partners. The S7-1500 might not see this problem.. if the resource pool to rotate through is large enough.

(sigh)
~

Thanks for your response. I've seen this document before. I've done more tests and found out that it takes around 1 minute for the connection to be fully released before it can be re-established which is not ideal when you need to send data every second.

One workaround is to keep the connection open and just use TSEND to send data and only close the connection when there's an error. The problem with this method is that you no longer have the handshake mechanism to ensure data has been sent to the partner.

Apparently TSEND will not detect the connection failure immediately! It takes around 15 seconds for TSEND to detect a failure which means any data sent in this period will be lost!

qwazee

 

EMTABAR

<snip>
It seems the connection resource is still occupied for more than 10 seconds after TDISCON is called despite TDISCON's "DONE" status flag being set straightaway.
</snip>

Hello.

Your finding is shocking yet not surprising. I am not aiming to defend Siemens' design choices on this topic. I only thought I should mention that what you found is documented. Please see the attached.

This design decision severely cripples the S7-1200 to have multiple communication partners. The S7-1500 might not see this problem.. if the resource pool to rotate through is large enough.

(sigh)
~