Overview
Two different concepts are available in the PLC for calling OPC UA methods:
- 1. RPC methods and
- 2. Job methods
The fundamental difference between the two concepts is the context of processing in the PLC and the implementation in the PLC code.
The following table illustrates this relationship.
Type | Processing | PLC code |
|---|---|---|
RPC method | Within a PLC cycle | OPC UA method is represented by a PLC method. |
Job method | Over several PLC cycles | OPC UA method is represented by a PLC function block. |
Generally speaking, one can define: Job methods are the method of choice if a method call takes a "long" time, i.e. can take several PLC cycles. The processing of RPC methods, on the other hand, must be "fast", otherwise there is a risk of cycle overruns. So Job methods are usually selected. Programming in the PLC is somewhat more complex, but the decoupling from the PLC cycle is a great advantage that justifies this effort.