Endress+Hauser Proline Promass 84 MODBUS RS485 Operating Instructions Manual page 41

Proline Promass 84 MODBUS RS485
Endress+Hauser
Data types
The following data types are supported by the measuring device:
• FLOAT (floating-point numbers IEEE 754)
Data length = 4 bytes (2 registers)
Byte 3
SEEEEEEE EMMMMMMM
S = sign
E = exponent
M = mantissa
• INTEGER
Data length = 2 bytes (1 register)
Byte 1
Most significant byte Least significant byte
(MSB)
• STRING
Data length = depends on device parameter,
e.g. illustration of a device parameter with a data length = 18 bytes (9 registers):
Byte 17 Byte 16
Most significant byte
(MSB)
Byte transmission sequence
Byte addressing, i.e. the transmission sequence of the bytes, is not specified in the MODBUS
specification. For this reason, it is important to coordinate the addressing method between the
master and slave during commissioning. This can be configured in the measuring device by means
of the "BYTE ORDER" parameter (see "Description of Device Functions" manual).
The bytes are transmitted depending on the option selected in the "BYTE ORDER" parameter:
FLOAT:
Selection 1st
1 – 0 – 3 – 2* Byte 1
(MMMMMMMM)
0 – 1 – 2 – 3 Byte 0
(MMMMMMMM)
2 – 3 – 0 – 1 Byte 2
(EMMMMMMM)
3 – 2 – 1 – 0 Byte 3
(SEEEEEEE)
* = Factory setting
S = sign
E = exponent
M = mantissa
Byte 2 Byte 1
MMMMMMMM
Byte 0
(LSB)
...
...
2nd
Byte 0
(MMMMMMMM)
Byte 1
(MMMMMMMM)
Byte 3
(SEEEEEEE)
Byte 2
(EMMMMMMM)
Byte 0
MMMMMMMM
Byte 1 Byte 0
Least significant byte
(LSB)
Sequence
3rd 4th
Byte 3 Byte 2
(SEEEEEEE) (EMMMMMMM)
Byte 2 Byte 3
(EMMMMMMM) (SEEEEEEE)
Byte 0 Byte 1
(MMMMMMM) (MMMMMMM)
Byte 1 Byte 0
(MMMMMMMM) (MMMMMMMM)
Operation
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