YSI DIQ/S 182-MOD System 182 - Manual (Page 121)

System 182 Modbus connection
7 - 9 ba76025e01 02/2012
Note
The counting method of the Modbus registers and Modbus bits and the
allocation of MSB and LSB is different from the usual method of most
programming languages.
*MSB = Most significant bit, LSB = Least significant bit
7.4.4 Data formats
The sensor data in the sensor data block (see section 7.4.3) are
available in the Float 32, INT16 and INT8 data formats.
Float 32 The data for the main and secondary measured values are transmitted
in the IEE-754 standard 32-bit floating point format.
MSB = Most significant bit, LSB = Least significant bit
If not all of the bits of the exponents are 0, the value is calculated
according to:
If all of the bits of the exponents are 0, the value is calculated according
to:
A value is 0 if all the bits of both the exponents as well as the mantissa
are 0.
Modbus Usually
Counting start of the register 1 0
MSB* allocation of the register Bit 1 Bit 15
LSB* allocation of the register Bit 16 Bit 0
Bit representation Byte Bit
4 31 - 24 S = sign (bit 31)
E = Exponent (Bit 30-23)
M = mantissa (bits 22-0)
3 23 - 16
2 15 - 08
1 07 - 00
MSB* LSB*
S E E E E E E E
E M M M M M M M
M M M M M M M M
M M M M M M M M
) 2 ... 2 2 2 1 ( 2 1 23
0
3
20
2
21
1
22
127 − − − − − ⋅ + + ⋅ + ⋅ + ⋅ + ⋅ ⋅ − =
b b b b
E S M M M M V
) 2 ... 2 2 2 ( 2 1 23
0
3
20
2
21
1
22
126 − − − − − ⋅ + + ⋅ + ⋅ + ⋅ ⋅ ⋅ − =
b b b b
S M M M M V