E+E Elektronik HTS801, User Manual

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User Manual HTS801
Humidity and Temperature Sensor for High Humidity and Chemically Polluted Conditions | 45
6.3 Modbus RTU Example
The HTS801’s Modbus address is 230 [0xE6].
Please refer to
▪.
MODBUS APPLICATION PROTOCOL SPECIFICATION V1.1b3, chapter 6:
www.modbus.org/docs/Modbus_Application_Protocol_V1_1b3.pdf
▪.
E+E Application Note Modbus AN0103 (available at www.epluse.com/hts801 )
Read the temperature (FLOAT32) T = 25.6787014007568359375 °C from register address 0x3EA
:
Master (e.g. PLC) HTS801
Request [Hex]:
Modbus
address
Function
code
Starting
address Hi
Starting
address Lo
Qty. of
registers Hi
Qty. of
registers Lo
CRC
E6 03 03 EA 00 02 F2 6C
Response [Hex]:
Modbus
address
Function
code
Byte
count
Register 1
value Hi
Register 1
value Lo
Register 2
value Hi
Register 2
value Lo
CRC
E6 03 04 6D FB 41 CD 53 AB
Fig. 40 Example temperature query
Decoding of floating point values:
Floating point values are stored according to IEEE754. The byte pairs 1, 2 and 3, 4 are transformed as follows
(numbers.taken.from.T.reading.Modbus.request/response.example.above):
Modbus response [Hex]
Register 1 Hi Register 1 Lo Register 2 Hi Register 2 Lo
6D FB 41 CD
MMMMMMMM MMMMMMMM SEEEEEEE EMMMMMMM
Fig. 41 Modbus response
IEEE754
Register 2 Hi Register 2 Lo Register 1 Hi Register 1 Lo
41 CD 6D FB
0100 0001 1100 1101 0110 1101 1111 1011
SEEE EEEE EMMM MMMM MMMM MMMM MMMM MMMM
Decimal value: 25.6787014007568359375
Fig. 42 Data representation according to IEEE754