4 example, Example – YSI IQ S ENSOR N ET Field bus linking User Manual
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IQ S
ENSOR
N
ET
Field bus linking
Communication with field buses
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* MSB = Most significant bit, LSB = Least significant bit
4.2.4 Example
Query of the sensor data
block for sensor S02
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.
Modbus
Usually
Count start of the register
1
0
MSB* allocation of the register
Bit 1
Bit 15
LSB* allocation of the register
Bit 16
Bit 0
Modbus query
Byte
Value
Information
Meaning of the value
1
01h
Modbus address of
the IQ S
ENSOR
N
ET
01h --> 1
2
04h
Function
04h --> 4
Read Input Register
see section 4.2.2
3
00h
Start address HI
0008h --> 8
Start with register 9
(Modbus counting method)
4
08h
Start address LO
5
00h
Number of HI regis-
ters
0008h --> 8
8 registers
6
08h
Number of LO regis-
ters
7
70h
CRC (HI)
Checksum (CRC)
8
0Eh
CRC (LO)