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7. Modbus
7.1
Modbus
7.1.1
About
The SGC controller supports a custom protocol based on the standard Modbus over an RS-485 layer. The controller
operates in a server mode and responds to commands received from an external Modbus client.
This document will only describe the information required to communicate with the controller using the Modbus protocol.
For more information about Modbus in general and the Modbus protocol, refer to the documentation freely available at
http://www.modbus.org.
Refer to the Modbus tables, available for download at www.deif.com, to see how the controller data is mapped to the
Modbus addresses.
7.1.2
Connection details
The controller uses Modbus RTU as the transmission mode (not Modbus ASCII).
Byte format for communication
• Start bit: 1
• Data bits: 8
• Parity: None
• Stop bit: 1
• Cyclic Redundancy Check (CRC)
Setting up Modbus communication
1. Connect the controller terminals 31 and 32 to the SMPS terminals A and B.
• Use a two-core shielded cable for the connection.
• Use wires with different colours for terminals 31 and 32.
• Connect the wires correctly to make sure that they do not get short with other wires.
• Do not use multi-strand wires for the connection.
2. Connect the controller terminal 30 to the ground of the SMPS. If the SMPS does not have a ground connection, leave the
controller terminal 30 open.
• Use a two-core shielded cable for the connection.
• Do not use multi-strand wires for the connection.
3. Find the server ID from the SMPS and configure the same ID in the controller.
4. Enable the controller in the configuration of the SMPS after hardware connections are made.
7.1.3
RS-485 communication settings
• Server ID: 1 to 247
• Baud rate: 1200/2400/4800/9600/19200/38400/57600/115200 bps
• Parity: None/Even/Odd
• Stop bit: 1, 2
• Recommended polling frequency: 50 Hz
• No response timeout: 250 ms
User manual 4189341355A EN
Page 80 of 92
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