WinCC 7.4 loses connection with PLC if alarms are used

Hi all,

I have a strange problem with a WinCC version 7.4 project. If alarms from the alarm list are used, the connection between WinCC and PLC is lost within 0-60 seconds. This only happens with a real PLC (S7-317-2-DP) and the PC with WinCC, not while testing with a SIM PLC (WinLC RTX) and the same PC with WinCC.
As far as I know it's a standard alarm setup, reading bits from an alarm words in a DB in the PLC.
The PLC also communicates with another PLC using an S7 connection and BSEND/BRCV blocks, sending a 200 byte DB and receiving a 200 byte DB.
The CP card diagnostics don's show anything strange.
What could it be?

Has the project worked ever before, or is this a new project?

What type of messaging are you using:
1) Variable/bit triggered messages, or 2) block-related messages with Alarm_S or Alarm_D?

If 1) is in alarm logging a function for "Format DLL" entered, or tags at "Status tag" or "Acknowledgement tag"? Are the tags available and of correct datatype?

You can also check the logfiles of the S7 channel driver (S7 protocol suite) in WinCC/diagnose folder. But the error messages there are not always helpful.

Hi Thomas,
Solved it!
I'm using method 1) bit triggered messages.
As for tags available, the logged errors in the SIMATIC_S7_Protocol_Suite_02.LOG in C:\Program Files (x86)\Siemens\WinCC\diagnose showed error D801, indicating incorrect addressing.
Looking at the quality code of the tags indeed showed some errors. These are now fixed and the connection is no longer lost.
But it's strange incorrect addressing would break the connection entirely..
Thanks for your help!

crosspost Siemens forum https://support.industry.siemens.co...re-used/178319/?page=0&pageSize=10#post711822