Transmission Format (Integer, Float, Double And Text Values) - JUMO LOGOSCREEN nt Interface Description

4 Modbus protocol description

4.7 Transmission format (integer, float, double and text values)

Integer values
Example
Float values
Example
22
When using Modbus, integer values are transmitted in the following format:
first the HIGH byte, then the LOW byte.
Request the integer value from address 0x1017, when this address contains
the value "4" (word value: 0x0004).
Request: 01031017000130CE (CRC16 = CE30)
Response: 0103020004B987 (CRC16 = 87B9)
When using Modbus, float values are processed in the IEEE 754 standard
format (32-bit), but with the difference that bytes 1 and 2 are swapped with
bytes 3 and 4.
Single float format (32-bit) according to standard IEEE 754
SEEEEEEE
Byte 1
S = sign bit
E = exponent (complement to base 2)
M = 23bit normalized mantissa
Mdobus float format
Modbus address x
MMMMMMMM
Byte 3
Request the float value from address 0x0035, when this address contains the
value "550.0" (0x44098000 in IEEE 754 format).
Request: 140300350002D6C0 (CRC16 = C0D6)
Response: 140304800044096434 (CRC16 = 3464)
After the transmission from the device, the bytes of the float value must be
swapped accordingly.
Many compilers (e. g. Microsoft Visual C++) store the float values in the
following order:
Float value
Address x
MMMMMMMM
Byte 4
Please check how float values are stored in your application. If necessary, the
bytes will have to be swapped accordingly in your interface program, after
they have been fetched from the paperless recorder.
EMMMMMMM MMMMMMMM
Byte 2
MMMMMMMM
Byte 4
Address x+1
MMMMMMMM
Byte 3
MMMMMMMM
Byte 3
Modbus address x+1
SEEEEEEE
Byte 1
Address x+2
EMMMMMMM
Byte 2
Byte 4
EMMMMMMM
Byte 2
Address x+3
SEEEEEEE
Byte 1