Modbus is a data communications protocol originally published by Modicon (now Schneider Electric) in 1979 for use with its programmable logic controllers (PLCs). Modbus has become a de facto standard communication protocol and is now a commonly available means of connecting industrial electronic devices (Source https://en.wikipedia.org/wiki/Modbus).
Modbus is a very simple standard which is transfering discrete inputs and outputs or registers (double word).
Currently Game4automation can be only used as a Modbus master. Client support will be added in one of the next releases.
If Game4automation is acting as a Modbus master the clients need to poll and write their values to Game4automation. The modbus master is not acting actively on his own. The Modbus server is always on the computers IP adress woth the standard port 502.
The Modbus interface is added to the Scene by selecting Tools > game4automation > Add Component > Interface > Modbus or by adding the script ModbusInterface to an empty GameObject.
Because Modbus is only transferring discrete inputs or outputs or words and because there is no standard data structure for describing the content inside these data you need to define how to interpret the Modbus data inside Game4automation.
Each PLCInput or PLCOuput signal needs to hava an attached ModbusData component. This component is defining with its properties how the bits and bytes should be interpreted by Game4Automation.