To simplify the implementation of hardware that is connected via certain standardized physical connection layers and protocols, those are implemented as Bridges.
M-Bus is a widely used standard for fieldbus communication. It enables connection to M-Bus devices like meters.
This bridge depends on jMbus, a user guide for it can be found at https://www.openmuc.org/m-bus/user-guide/.
Note: For jMbus to work you need to install the native part of RxTx which is a library for serial port communication jMbus is dependent on. See paragraph 2.5 for further information.
For Linux users: In case the RxTx library cannot be found under /usr/lib/jni you can try to move all .so files of that directory to /usr/lib (see OpenEMS Community).
Modbus is a widely used standard for fieldbus connections. It is used by all kinds of hardware devices like photovoltaics inverters, electric meters, and so on.