MODBUS Communication
– General
5
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TI 12J06J01-00EN-P
1. General
Optical Dissolved Oxygen sensors are slave devices which can be configured or are sending
process data using Bi-directional digital communication (RS485, half-duplex) with full MODBUS
(RTU) support. The power for the Optical Dissolved Oxygen sensors must be supplied by a HOST
or by a separate power supply in the range +7VDC up to +30VDC. Maximum power of the Optical
Dissolved Oxygen sensors is 1W in active mode, and 150mW in stand-by mode.
1.1 MODBUS setup
The following list shows the required setting by HOST to establish communication between the
HOST as master device and the Optical Dissolved Oxygen sensor as slave device. The procedure
for changing list items is explained in the following chapters in this document.
Slave address
: 1
Serial Profile
: 19200 bps, 8 data bits, No parity, 2 stop bits
NOTE
Slave address and Serial Profile are configurable as explained in this document.
In case of using multiple Optical Dissolved Oxygen sensors in a bus system, connected to one HOST,
the Slave addresses of all the Optical Dissolved Oxygen sensors must be unique. Because initial
setting of address is 1 it is recommended to change the initial address value to prevent communication
conflicts in case a new purchased Optical Dissolved Oxygen sensor is added to the bus.
Serial profile of the slave device(s) must be the same as the HOST.
1.2 Function code / Exception code
MODBUS Function codes used for DO71 and DO72:
Function
Function code (hex)
Read Hold Register
03
Write Single Register
06
Write Multiple Registers
10
Exception codes used for DO71 and DO72:
Name
Exception code
Meaning
Illegal Function
0x01
The Function code received is not an
allowable action for the slave
Illegal Data Address
0x02
The Data Address received is not an
allowable address for the slave