OPC UA features for Siemens S7-1500 - by: gregkuha60

hello

I'm planning to do an integration with the built in opc server in the Siemens CPU 1516-3
So i'm reading the manual, "S7-1500, ET 200MP, ET 200SP, ET 200AL, ET 200pro Communication"
it says "..
If you access specific tags regularly (recurring access), you should use the functions "RegisteredRead" and "RegisteredWrite"
.."
Has any a clue what it means?
Thanks for any suggestion
Regards
Greg