Modbus Rtu Example - E+E Elektronik HTS801 User Manual

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)
Request [Hex]:
Modbus
address
E6
Response [Hex]:
Modbus
address
E6
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
6D
MMMMMMMM
Fig. 41 Modbus response
IEEE754
Register 2 Hi
41
0100 0001
SEEE EEEE
Decimal value: 25.6787014007568359375
Fig. 42 Data representation according to IEEE754
Function Starting Starting
code address Hi address Lo
03 03
Function Byte Register 1
code count value Hi
03 04
Register 1 Lo
FB
MMMMMMMM
Register 2 Lo
CD
1100 1101
EMMM MMMM
Qty. of Qty. of
registers Hi registers Lo
EA 00 02
Register 1 Register 2
value Lo value Hi
6D FB 41
Register 2 Hi
41
SEEEEEEE
Register 1 Hi
6D
0110 1101
MMMM MMMM
Humidity and Temperature Sensor for High Humidity and Chemically Polluted Conditions | 45
User Manual HTS801
HTS801
CRC
F2 6C
Register 2
CRC
value Lo
CD 53 AB
Register 2 Lo
CD
EMMMMMMM
Register 1 Lo
FB
1111 1011
MMMM MMMM