Appendix B _________________________________________________________ Modbus Reference
VAISALA _______________________________________________________________________ 105
NOTE
A complete 32-bit floating point value should be read and written in a
single Modbus transaction (for example, function codes 05, 06, and 22 do
not have an effect on floating point values).
16-Bit Integer Format
16-bit integer values are scaled to include the necessary decimals (see
corresponding register table for the scaling factor) and represented as
described in the following table.
Table 41
16-bit signed integer format details
Value
Description
0x0000…0x7FFE
Value in range 0…32766
0x8002…0xFFFF
Value in range -32766…-1 (2’s complement)
0x7FFF
Value is 32767 or larger (positive infinity)
0x8000
Value is not available (quiet NaN)
0x8001
Value is -32767 or smaller (negative infinity)
Trying to write special values 0x7FFF, 0x8000, or 0x8001 in a 16-bit
integer register is ignored to avoid unintended result.
NOTE
Some values may exceed the signed 16-bit range even in normal
operation. Please access such values using the floating point registers
instead.
Measurement Data (Read-Only)
Table 42
HMW90 Modbus Measurement Data Registers
Name Metric float Metric integer Metric
unit
Non-metric
float
Non-metric integer Non-metric
unit
RH
0003…0004 0258 (×0.01)
%RH 6403…0004 6458 (×0.01)
%RH
T
0005…0006 0259 (×0.01)
°C
6405…0006 6459 (×0.01)
°F
Td
0007…0008 0260 (×0.01)
°C
6407…0008 6460 (×0.01)
°F
Tdf
0009…0010 0261 (×0.01)
°C
6409…0010 6461 (×0.01)
°F
dTd
0011…0012 0262 (×0.01)
°C
6411…0012 6462 (×0.01)
°F
Tw
0013…0014 0263 (×0.01)
°C
6413…0014 6463 (×0.01)
°F
a
0015…0016 0264 (×0.01)
g/m3 6415…0016 6464 (×0.01)
gr/ft3
x
0017…0018 0265 (×0.01)
g/kg
6417…0018 6465 (×0.01)
gr/lb
h
0019…0020 0266 (×0.01)
kJ/kg 6419…0020 6466 (×0.01)
btu/lb
Available measurements depend on the instrument configuration. Values
may be unavailable also in case of device failure. Read status registers or
exception status outputs to check for failures.
