Endress+Hauser Proline Promag 300 - Byte Order

Description of device parameters Proline Promag 300 Modbus RS485
152 Endress+Hauser
Additional information Options
Picklist ASCII option:
• 0 = Even option
• 1 = Odd option
Picklist RTU option:
• 0 = Even option
• 1 = Odd option
• 2 = None/1 stop bit option
• 3 = None/2 stop bits option
Byte order 
Navigation  Expert → Communication → Modbus config. → Byte order (7113)
Description Use this function to select the sequence in which the bytes are transmitted. The
transmission sequence must be coordinated with the Modbus master.
Selection • 0-1-2-3
• 3-2-1-0
• 1-0-3-2
• 2-3-0-1
Factory setting 1-0-3-2
Additional information Description
The byte sequence is not standardized by the Modbus protocol. However, if the host
system and the measuring device do not use the same byte sequence, correct data
exchange is not possible.
Changing the byte sequence in the host system often requires a extensive knowledge and
significant programming efforts. Endress+Hauser introduced the Byte order parameter
(→  152) for this reason.
This makes it possible to use the standard settings of the host system and change the byte
sequence on the measuring device by trial and error. If correct data exchange cannot be
achieved by changing the byte sequence, the settings for the byte sequence of the host
system must be adapted accordingly.
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 (→  152).
The bytes are transmitted depending on the selection in the Byte order parameter
(→  152):
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)