Providing Methods On The Opc Ua Server; Useful Information About Server Methods - Siemens SIMATIC S7-1500 Function Manual

9.3.5

Providing methods on the OPC UA server

9.3.5.1

Useful information about server methods

Providing user program for server methods
On the OPC UA server of an S7-1500 CPU (as of firmware V2.5), you have the option of
providing methods via your user program. These methods can be used by OPC UA clients,
for example to start a manufacturing job using the method call of the S7-1500 CPU.
OPC UA methods, an implementation of "Remote Procedure Calls", provide an efficient
mechanism for interactions between different communication nodes. The mechanism
provides both job confirmation and feedback values so you no longer have to program
handshaking mechanisms.
Using OPC UA methods, you can transfer data consistently without trigger bits/handshaking,
for example, or trigger specific actions on the controller.
How does an OPC UA method work?
An OPC UA method in principle operates like a know-how protected function block that is
called by an external OPC UA client in runtime.
The OPC UA client only "sees" the defined inputs and outputs. The content of the function
block, the method or algorithm, remains hidden to the external OPC UA client. The OPC UA
client receives feedback on successful execution and values returned by the function block
(method), or an error message if execution has not been successful.
As the programmer, you have full control over and responsibility for the program context in
which the OPC UA method runs.
Rules for programming a method and runtime behavior
● Make sure that the values returned by the OPC UA method are consistent with the input
values provided by the OPC UA client.
● Follow the rules on assigning name and the structure of parameters, and the permitted
data types (see description of the OPC UA server instructions).
● Behavior during runtime: The OPC UA server accepts one call per instance. The method
instance is not available for other OPC UA clients until the call has been processed by
the user program or has timed out.
The basic procedure for implementing a user program as a server method is set out below.
Communication
Function Manual, 11/2019, A5E03735815-AH
OPC UA communication
9.3 Using the S7-1500 as an OPC UA server
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