Read out a struct with S7+/OPC UA Siemens 1500 CPU
We wanted to communicate with a Step7 Plus or OPC UA driver with an Siemens 1500 CPU.
In the PLC we have defined a struct with 16 bits inside. We want to read out the struct in WinCC OA (like a struct). Which adress config do we need to use?
Thanks a lot!
Please have a look at the following thread:
viewtopic.php?f=16&t=10732&p=966029&hil ... ex#p966026
For me it looks like in this thread it is described that the usage of a bit struct is not possible when using the S7+ driver.
Senior Support Specialist
This same project with a OPC-UA client connected to the onboard OPCUA server of an S7-1516 PLC netted us the following results:
-the same project now requires about 4600 I/O, note: we are now only reading booleans we really need (no unused bits subscribed).
-the S7-1500 OPC-UA server cannot cope with the 4600 item load at a 2s internal polling rate (GoodOverload status values all over the place)
The maximum recommended item load for the PLC according to Siemens technical documentation is 2000 subscribed items at a 1s polling rate...
To access any serious amount of data in an S7-1500 you NEED to be able to subscribe to struct nodes somehow (assuming we do not recode everything to use arrays, which would render the code less readable). Subscribing to a struct node should count as 1 item for the OPCUA server if I'm not misinformed, much less than the 16 (and sometimes 32) bits that we need to subscribe now.
Also consider that this is a small project, we can and do fit projects 2 to 3 times bigger than the one mentioned above in S7-1500 plc's.
I'll be trying out the S7plus driver next, I can only hope it performs better so the effort of converting my codebase was not a complete waste of time.
Afraid we need a different PLC programming paradigm if we ever want to make the transition from S7 classic to its more modern counterparts.