Modbus Rtu Example; Maintenance And Service; Calibration And Adjustment; Definitions - E+E Elektronik EE431 User Manual

5.4.7.

Modbus RTU Example

Example of Modbus RTU command for reading the Temperature (float value) T = 26,953624 °C from the register
0x3EA.
Device EE431; Modbus address 66 [42 in HEX]
Reference document (chapter 6.3): http://www.modbus.org/docs/Modbus_Application_Protocol_V1_1b.pdf.
Read the temperature (FLOAT32) T from register address 0x3EA:
Master (e.g. PLC)
Request [Hex]:
Modbus
address
42
Response [Hex]:
Modbus
address
42
Fig. 8 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, Fig. 8):
Modbus response [Hex]
Register 1 Hi
A1
MMMMMMMM
Fig. 9 Modbus response
IEEE754
Register 2 Hi
41
0100 0001
SEEE EEEE
Decimal value: 26.953624725341796875
Fig. 10 Data representation according to IEEE754

6 Maintenance and Service

6.1

Calibration and Adjustment

6.1.1.

Definitions

Calibration: The specimen is compared with a reference and its deviation from the reference is documented.
Adjustment: The specimen is brought in line with the reference.
Function Starting Starting
code address Hi address Lo
03 03
Function Byte Register 1
code count value Hi
03 04
Register 1 Lo
06
MMMMMMMM
Register 2 Lo
D7
1101 0111
EMMM MMMM
Qty. of Qty. of
registers Hi registers Lo
EA 00 02
Register 1 Register 2
value Lo value Hi
A1 06 41
Register 2 Hi
41
SEEEEEEE
Register 1 Hi
A1
1010 0001
MMMM MMMM
User Manual EE431
Temperature Sensor
CRC
EB 48
Register 2
CRC
value Lo
D7 3B 04
Register 2 Lo
D7
EMMMMMMM
Register 1 Lo
06
0000 0110
MMMM MMMM
Duct and Immersion Temperature Sensor | 17