34 Issue
Number:
3
7.3 Data
Consistency
Data consistency provides a method of ensuring that all data is updated
at the same time, thus preventing any form of data skew.
Using data consistency can often put restrictions on data manipulation
within the master controller, and require data bytes or words to be
written in a certain order. Using data consistency can increase the
master controller cycle time, so it should only be used if really
necessary. (See section 5.2).
7.4 Profibus-DP
Data
Formats
All data formats can be set to have full data consistency or no data
consistency. The first cyclic data word is always the control word.
Non-cyclic
mode
Cyclic
words
Consistency Comments
1 3 Full
1 3
None
These modes are supported by
Mentor II and Commander SE
1
3
Full
8 bytes with full consistency,
available for backwards
compatibility with older modules
When the master initialises the network, it will transmit the configuration
byte to each slave. If the configuration byte matches one of the three
modes above, the slave will automatically configure itself for this type of
data.
If the telegram does not match any of the above data formats, the node
will not be initialised and the master will indicate that there is an error on
the network.