Mitsubishi Electric MelcoREMOTE, Installation And Operation Manual

Page: 22 / 52

Page 22 of 52
10. Connecting Modbus Devices
MelcoREMOTE can act as a Modbus Master device and be configured to communicate with external Modbus Slave
devices, to expand its I/O.
The following types of Modbus Slave device can be connected to MelcoREMOTE :
- Devices supporting the Modbus RTU protocol via RS-485 (e.g. MelcoBEMS MINI (A1M) )
- Devices supporting the Modbus TCP protocol via Ethernet
10.1. Modbus RTU devices
The MelcoREMOTE has two RS-485 ports which can be used independently to connect to external devices which
support the Modbus RTU communication protocol.
Using RS-485, multiple devices can be connected together in a daisy chain bus formation. The maximum length of the
bus is 1000m, and up to 32 devices can be connected together on the bus. The following image shows two
MelcoBEMS MINI Modbus devices connected in a daisy-chain formation to a MelcoREMOTE.
Every Modbus device has two connections named ‘
A ’ and ‘ B ’ (although some devices use different naming
conventions, such as ‘ D+ ’ and ‘ D- ‘). All ‘ A ’ connections should be wired together in the chain, as should all the ‘ B ’
connections. MelcoREMOTE also requires a common ground between all Modbus devices connected to it.
Caution:
Use only shielded twisted-pair cables for the RS-485 network to reduce the possibility of interference with
radio communications services. Using shielded cables ensures that you maintain the appropriate EMC
classification for the intended environment.
All shields must be tied to an appropriate Earth point within the installation panel.