wtw DIQ/S 182-MOD System Operating Manual page 120

Modbus connection
7 - 10
Note
If the measured value is equal to 0, check the measured value status.
If the measured value status is not equal to 1, an error has occurred
and the measured value is invalid.
Note
The Modbus protocol does not define how the bytes of 32-Bit-IEEE-754
floating point numbers should be ordered.
Apart from the byte order described in the bit representation, another
order of the bytes is also possible.
Opposite to the order described, the two lower bytes have been
exchanged with the two upper bytes in this order (b4 b3 b2 b1 - b2 b1
b4 b3).
For Modbus applications that can independently interpret floating point
numbers (or allow to select a data format for certain registers), the byte
order the data interpretation is based on should be checked.
INT16 In the INT16 format, the data for the sensor model and status info is
transmitted. The data consists of two bytes. The assignment is carried
out in Motorola format ("big-endian", the higher value byte first).
Bit representation
MSB
INT8 All other data is transmitted in the INT8 format. This data consists of
one byte.
The data for the measured value status of the main and secondary
measured values are encoded jointly into a single byte. Bits 7-4 encode
the status of the main measured value, bits 3-0 encode the status of the
secondary measured value.
Information
LSB
High byte
Low byte
System 182
ba75504e07 04/2012