OTT HydroMet SUTRON XLINK 100, Operation & Maintenance Manual

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19.1.2 The Station as a Modbus Client
The station is capable of operating as a Modbus client. It can collect data from sensors using the Modbus
protocol. When setup to collect data from Modbus sensors, the station will periodically issue a client read
register message on the data bus. Sensors on the bus act as servers: they will reply to the message,
providing ‘register values’ which translate to sensor readings.
Multiple Modbus sensors may be connected to the RS-485 bus. However, each sensor must be
programmed with a unique Device ID. If the sensors do not have unique IDs, they will cause collisions on
the data bus, resulting in failures to collect sensor data. The station is NOT capable of changing Device IDs.
Please refer to the sensor’s documentation for information on how to change their IDs.
Please note that the station does NOT have the ability to write Modbus registers.
19.2 Modbus Hardware Interface
There are several interfaces that support Modbus communication:

RS-485

RS-232

Cell modem
The station may be a Modbus client or a Modbus server over RS-485 and over RS-232. The station may
only be a Modbus server over the cell modem.
Each interface can be setup independently of the other one. Each interface has its own setup. This means
that the station could be a Modbus client on RS-485 and a Modbus server on Cell modem at the same
time.
19.2.1 Wiring Modbus RS-485
The station has a half-duplex RS-485 interface. That means that the same lines are used for sending and
receiving data.
Only two lines need to be connected to use RS-485:

RS-485 A

RS-485 B
When wiring, connect the Modbus client's RS- 485 A line to the station’s R S-485 A Line. Do the same for
RS-485 B.
19.2.2 Wiring Modbus RS-232
When using RS-232 for Modbus communications, only three of the lines in the DB9 connector are
necessary:

TX

RX

Ground