System integration
Proline Promass E 300 Modbus RS485
72
Hauser
9.3.5
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 or match the addressing
method between the master and slave during commissioning. This can be configured in
the measuring device using the
Byte order
parameter.
The bytes are transmitted depending on the selection in the
Byte order
parameter:
FLOAT
Sequence
Options
1.
2.
3.
4.
1 – 0 – 3 – 2 *
Byte 1
(MMMMMMMM)
Byte 0
(MMMMMMMM)
Byte 3
(SEEEEEEE)
Byte 2
(EMMMMMMM)
0 – 1 – 2 – 3
Byte 0
(MMMMMMMM)
Byte 1
(MMMMMMMM)
Byte 2
(EMMMMMMM)
Byte 3
(SEEEEEEE)
2 – 3 – 0 – 1
Byte 2
(EMMMMMMM)
Byte 3
(SEEEEEEE)
Byte 0
(MMMMMMM)
Byte 1
(MMMMMMM)
3 – 2 – 1 – 0
Byte 3
(SEEEEEEE)
Byte 2
(EMMMMMMM)
Byte 1
(MMMMMMMM)
Byte 0
(MMMMMMMM)
* = factory setting, S = sign, E = exponent, M = mantissa
INTEGER
Sequence
Options
1.
2.
1
–
0
– 3 – 2 *
3 – 2 –
1
–
0
Byte 1
(MSB)
Byte 0
(LSB)
0
–
1
– 2 – 3
2 – 3 –
0
–
1
Byte 0
(LSB)
Byte 1
(MSB)
* = factory setting, MSB = most significant byte, LSB = least significant byte
STRING
Presentation taking the example of a device parameter with a data length of 18 bytes.
Sequence
Options
1.
2.
...
17.
18.
1
–
0
– 3 – 2 *
3 – 2 –
1
–
0
Byte 17
(MSB)
Byte 16
...
Byte 1
Byte 0
(LSB)
0
–
1
– 2 – 3
2 – 3 –
0
–
1
Byte 16
Byte 17
(MSB)
...
Byte 0
(LSB)
Byte 1
* = factory setting, MSB = most significant byte, LSB = least significant byte
9.3.6
Modbus data map
Function of the Modbus data map
The device offers a special memory area, the Modbus data map (for a maximum of 16
device parameters), to allow users to call up multiple device parameters via Modbus RS485
and not only individual device parameters or a group of consecutive device parameters.
Grouping of device parameters is flexible and the Modbus master can read or write to the
entire data block simultaneously with a single request telegram.
