2 Modbus protocol description
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2.6.2 Floating-point values
For floating-point values, device type 703571 operates using the IEEE 754 standard format
(32-bit), but with the difference that bytes 1 and 2 are interchanged with bytes 3 and 4.
Example
In this example, the controller setpoint value at address 0x122F of device type 703571 is to be
extracted. The value here is to be 20.0 °C (0x41a00000 in the IEEE 754 format).
Single-precision floating-point format (32-bit) acc. to IEEE 754 standard, "Float (LSB)"
SEEEEEEE EMMMMMMM MMMMMMMM MMMMMMMM
Byte 1 Byte 2 Byte 3 Byte 4
S-Sign bit
E - Exponent (two's complement)
M - 23-bit normalized mantissa
Modbus floating-point format, "Float (MSB)"
Modbus address x Modbus address x+1
MMMMMMMM MMMMMMMM SEEEEEEE EMMMMMMM
Byte 3 Byte 4 Byte 1 Byte 2
Data query:
01 03 12 2F 00 02 F0 BA
Slave Function code Address of
1st word
Number of
words
CRC
Response (values in Modbus floating-point format):
01 03 04 00 00 41 A0 CA 1B
Slave Function code Bytes
read
Floating-point value in
Modbus floating-point format
CRC
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