Using the Ignition Siemens S7-400 driver (version 7.7.5). I can successfully read address types such as Input Words using an opc item path such as “[device]IW0”.
However, I am having issues reading data block addresses.
For example, the PLC has data in address DB40.DBD8
I have tried several formats in the OPC item path with no luck.
Programmer supplied me with Data Base addresses of:
DB90.DBD0
DB90.DBD4
DB90.DBD8
DB90.DBD12
DB90.DBD16
DB90.DBD20
I have tried the “DB90.D0” approach but the tag fails.
I know the connection is good because I am able to bring back the “HostName” string and it returns the correct valve.
What am I missing??
I would be interested in knowing why the built in OPC UA server is a better alternative.
Tried it out on a project not too long ago, and it didnt seem to give me as a designer anything worth writing home about. Tag data type was wrong, no description etc…
As @deon.korb said… you get browsing and symbolic tag access, as well as access to optimized DBs, and you don’t need to make all the other configuration changes. Efficiently accessing structures is a bit of a pain, so there’s a trade off, but that’s Ignition’s fault more than anything.
OPC UA is the the official method endorsed by Siemens for external access. The S7 protocol is not open or documented, and everybody accessing tags that way, including us, is doing it with reverse engineered code (whether they did it themselves or licensed a library from somebody else who did it).