Liquidew I.S. User Manual
54
97092 Issue 5.3, September 2021
APPENDIX B
MODBUS RTU
Once the protocol has been set the monitor will communicate in accordance with the standard
Modbus RTU protocol.
The
Read Holding Registers
command should be used to read the registers listed in the register
map. When two registers are listed in the table both registers must be read using a single command.
Note that the least significant word is sent first, for example - for dew point - register 40517 is the
least significant word and 40518 is the most significant word.
It should also be noted that the actual address is that stated, minus 40000, i.e. 40517 is physically
517.
Example: Getting the dew-point value using Modbus RTU
Register Numbers:
Function
Register Name
Texmate ASCII
Modbus RTU
BARG
RESULT
254
40515/40516
Dew Point_C
CH1
253
40517/40518
psig
CH2
252
40519/40520
There is often an offset of -1 for the register address, depending on your software/PLC system. To
read the dew-point value software, read holding registers 516-517:
The highlighted value
0xFFFFFDE2
is a 32 bit signed integer .. so
-542
There is a scaling multiplier of 0.1, so -542 x 0.1 = -
54.2 °C
which is the value shown on the monitor.
