nVent RAYCHEM DigiTrace TCONTROL-CONT-03 Anleitung Seite 13

2 Protocol description
2.7 Transmission format (integer, float and text values)
Integer values
Integer values are transmitted via the Modbus in the following format: The high byte first,
followed by the low byte.
Example
Request of the integer value of address 0x0021, if value "4" (word value 0x0004) is written
under this address.
Request: 01 03 0021 0001 (+ 2 bytes CRC16)
Response: 01 03 02 0004 (+ 2 bytes CRC16)
Float values
In the case of float values, the Modbus operates with the IEEE-754 standard format
(32bits), the only difference being that byte 1 and 2 are changed over with byte 3 and 4.
Single-float format (32bit) as per IEEE 754standard
SEEEEEEE
Byte 1
S - sign bit
E - exponent (two's complement)
M - 23bits normalized mantissa
Modbus float format
Modbus address x
MMMMMMMM
Byte 3
Example
Request of the float value of address 0x0035, if value "550.0" (0x44098000 in IEEE-754
format) is written under this address.
Request: 01 03 0035 0002 (+ 2 bytes CRC16)
Response: 01 03 04 8000 4409 (+ 2 bytes CRC16)
Once transmission from the device is completed, the bytes of the float value need to be
changed over accordingly.
A large number of compilers (e.g. Microsoft Visual C++) store the float values in the
following order:
Float value
Address x
MMMMMMMM
Byte 4
Please find out the way float values are stored in your application. After the request, it
might be necessary to change the bytes over in the interface program you are using.
EMMMMMMM MMMMMMMM
Byte 2
MMMMMMMM
Byte 4
Address x+1
MMMMMMMM
Byte 3
MMMMMMMM
Byte 3
Modbus address x+1
SEEEEEEE EMMMMMMM
Byte 1
Address x+2
EMMMMMMM
Byte 2
Byte 4
Byte 2
Address x+3
SEEEEEEE
Byte 1
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