Michell Instruments Promet I.S. User Manual page 60

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
map. When two registers are listed in the table both registers must be read using a single command.
Note that the least signifi cant word is sent fi rst, for example - for dew point - register 40517 is the
least signifi cant word and 40518 is the most signifi cant 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
BARG
Dew Point_C
psig
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.
52
command should be used to read the registers listed in the register
Register Name
RESULT
CH1
CH2
Promet I.S. User's Manual
Texmate ASCII
254
253
252
97221 Issue 5, March 2017
Modbus RTU
40515/40516
40517/40518
40519/40520