Data Endian Format - Leroy-Somer digitax st User Manual

The SYNC command will cause a single transfer of the previously grouped data and
stop any more data from being received by the drive. The SYNC command may be
repeated while in this state to allow another single transfer of data to the drive. Issuing
an UNSYNC command will revert the drive to continuous cyclic update of the received
data.
The FREEZE command will cause a single transfer of the previously grouped data and
stop any more data from being transmitted by the drive. The FREEZE command may be
repeated while in this state to allow another single transfer of data from the drive.
Issuing an UNFREEZE command will revert the drive to continuous cyclic update of the
transmitted data.
12.3

Data endian format

Table 12.2
Pr MM.08
When data is sent over the PROFIBUS-DP network it is transmitted as 8-bit bytes.
Therefore when a 32-bit word or 16-bit word is transmitted it is split into four or two 8-bit
bytes. It is important that the receiving node reconstructs the received 8-bit bytes in the
correct order to arrive at the 32-bit or 16-bit data value that was originally transmitted,
this order is known as the Data Endian Format and is shown in Table 12.3.
Table 12.3 Data endian format
Data
endian
format
Big
Little
Most PROFIBUS-DP master controllers use big endian format by default, many also
support little endian, however some older PLCs do not offer the facility to select big
endian format.
74
Data endian format
Default
Range
Access
16-bit value
Pr MM.08
Byte order
High byte first
0
Low byte second
Low byte first
1
High byte second
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OFF
OFF (0) or ON (1)
RW
Word order
High word first
Low word second
Low word first
High word second
SM-PROFIBUS-DP User Guide
32-bit value
Byte order
High byte first
Mid-high byte second
Mid-low byte third
Low byte fourth
Low byte first
Mid-low byte second
Mid-high byte third
High byte fourth
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