Hello

I am looking at the possibility of using OPC UA Method calls to implement communications between the PLC and a higher level computer.  I have downloaded and tested the Siemens example project to get an understanding of how OPC UA Method calls work.  

My question relates to implementing two way communications.  To me it appears that invoking a method call and passing in parameters from a remote pc facilitates communications from the client to the server (PLC).  For example a message from the OPC UA client to the server to move a product from one location to another.

But how would i initiate a message from the PLC to the client?  For example a request from the PLC to the client for a destination of a particular item '123456789'?

If i am to do this using only OPC UA it seems to me that i would have to simply listen to variables from the client and act on any change in state. 

Thanks

Hi,

here there are a sample program that exemplify data exchange between two PLC by OPC UA Method. Once it have both sides, you can use it as basis for your communication with a PC.