Modbus is an open communication protocol that has been established in industry for many years. Due to its low complexity, it is not only used in programmable logic controllers, but is also often supported by meters, sensors and in buildings. In modern building automation, Modbus cloud communication is often required.
For the cloud connection, the software module Universal Cloud Adapter is required. The Cloud Adapter can be installed on any Windows or Linux device (x86, x64 or ARM). The setup is explained in “Getting Started“. Alternatively, you can also use the AnyViz IoT Gateway.
Modbus RTU is a master/slave bus where the cloud adapter acts as a master and can read up to 30 slave devices with only one connection. Communication is established via an RS485 interface with a 2/3 wire connection.
Modubus TCP is a client/server protocol that requires one TCP connection per terminal device. Some devices act as a Modbus gateway and can forward requests to Modbus RTU devices.
FunctionalityModbus/TCP: For Modbus communication via Ethernet, the IP address or host name of a device must be specified. Each Modbus TCP participant corresponds to a Modbus connection in the AnyViz Cloud Adapter. The “Unit-ID” can be used to address either the registers of the TCP subscriber or the registers of the subordinate subscribers.
Modbus/RTU: For a Modbus RTU connection, the serial interface must first be selected and parameterized (e.g. baud rate, stop bit, parity). The respective slave device can then be addressed via the unit ID (also called slave ID).
Multiple connections can be created with the Cloud Adapter. Any number of data points can be created for each connection and exchanged with the cloud.
Usually all values are provided in Big-Endian format. However, devices that provide their data in little-endian format can be read correctly with the “swap” flag.
The Modbus register addressing starts with register 0, but some device manufacturers start with the number 1 in the device documentation. In this case, the number minus 1 should give the correct register address.
Some device descriptions use the Modicon convention. For example, if a register with the number 40.001 is written, it means register #1 and function code 3. Register 30.001 means register #1 with function code 4.
