The Unitronics company supplies (free of charge) the OPC server for the communication with their devices. This software is a part of the installation CD-ROM that is supplied with each unit by default.
Usage of the PROMOTIC OPC client component requires purchase of the PmOpcClient license. With the freeware version PmFree, or when developing the application (with development environment for tersting purposes), this component is always functional.
For this communication in the PROMOTIC system can be used: PmModbusMr - Driver for communication by the Modbus Master protocol.