1.5.12. Client API Interfaces

There are three different levels to enter the CODESYS V3 PLC network.

The lowest level is to enter the network in the runtime system itself. This is typically used, if you write your own component and want to communicate with another plc.

The next level is the Gateway Client. This is typically used by a PlugIn in CODESYS or by CODESYS itself.

The highest interface is the PLCHandler. It provides to enter the communication network from any other proprietary client.

1.5.12.1. Channel client (CmpChannelClient)

The channel client component can be used from a component in the runtime system to enter the PLC communication network. The channel client can be used to open the communication to another PLC and to send native online service though this channel.

1.5.12.2. Gateway client (GwClient)

The Gateway-Client has a native C++ interface, so it can be used from .NET and C++ clients (like PlugIns in CODESYS). This interface provides to open the communication and to send native online service though this channel. In this layer, no symbolic access to variables in possible! To use symbolic access, you have to use the PLCHandler interface.

1.5.12.3. PLCHandler

This is the highest level API that is provided by 3S.

The PLCHandler is a C++-class which on a comfortable level provides services for the communication between a client (e.g. visualization) and a 3S Automation-Alliance compliant PLC (controller).

The following features and services are available:

  • Establishing and terminating the communication with the PLC

  • Reading all variables on the PLC

  • Cyclic reading of variables’ values from the PLC

  • Synchronous reading of variables’ values from the PLC

  • Synchronous writing of variables’ values to the PLC

  • Possibility of instancing for the purpose of a simultaneous

    communication with several PLCs

  • Automatic reconnecting with the PLC after an break of the connection

  • Automatic restart after a program download from CODESYS to the PLC

  • Data transfer to and from PLC

Thus the PLCHandler can be used as a basic component for OPC Servers or visualizations. The Handler is delivered as a SDK, i.e. all C++ header files, the static link library (PLCHandler.lib resp. PLCHandlerComplete.lib) and a sample program (main.cpp) are part of the package.

The PLCHandler supports beneath the CODESYS V3 generation runtime systems additionally the CODESYS V2.x generation runtime systems! So you only have to handle one interface for all runtime systems in the field.