E+E Elektronik EE212, Руководство пользователя

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User Manual EE212
Modular Humidity and Temperature Sensor | 18
5.4 Modbus RTU Example
The EE212’s Modbus address is 46 [0x2E].
Please refer to
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MODBUS APPLICATION PROTOCOL SPECIFICATION V1.1b3, chapter 6:
www.modbus.org/docs/Modbus_Application_Protocol_V1_1b3.pdf
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E+E Application Note Modbus AN0103 (available at www.epluse.com/ee212 )
Read the temperature (FLOAT32) T = 25.087642669677734375 °C from register address 0x19
:
Master (e.g. PLC) EE212
Request [Hex]:
Modbus
address Function
code
Starting
address Hi
Starting
address Lo
Qty. of
registers Hi
Qty. of
registers Lo
CRC
2E 03 00 19 00 02 12 53
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
2E 03 04 B3 7E 41 C8 53 AB
Tab. 6 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]
Byte 3 Byte 4 Byte 1 Byte 2
B3 7E 41 C8
MMMMMMMM MMMMMMMM SEEEEEEE EMMMMMMM
Tab. 7 Modbus response
IEEE754
Byte 1 Byte 2 Byte 3 Byte 4
41 C8 B3 7E
0100 0001 1100 1000 1011 0011 0111 1110
SEEE EEEE EMMM MMMM MMMM MMMM MMMM MMMM
Decimal value: 25.087642669677734375
Tab. 8 Data representation according to IEEE754