BECKHOFF BC3100 - Manual (Page 28)

PROFIBUS-DP basics
28 BC3100
Ensuring data consistency
Consistency of a station's data is ensured by the Profibus data transfer
protocol. Consistency throughout the entire process image must be
achieved by activating the "SYNC" and "FREEZE" operating modes in the
masters.
FREEZE and SYNC capability is preselected for the slave parameters (see
figure) and cannot be deactivated. The control software checks FREEZE
and SYNC.
Activation of response monitoring ensures that an error message is created
in the event of failure of the corresponding station belonging to the master
and that the control software is enable to initiate exception handling.
Response monitoring can be selected individually for each station.
Response monitoring on is the default. The COMProfibus software issues
a warning whenever monitoring is to be deactivated.
Inconsistencies may occur as the result of asynchronous access by the
controller CPU (mostly PLC) to the data area of the Profibus master. Data
consistency is ensured automatically with the configuration of a "multi-byte
signal" and module consistency in the COMProfibus configuration software
for IM308-C. With regard to further master interfaces, please consult the
corresponding manufacturers' manuals for an explanation.
The IM 308-C as Profibus DP master is a common PLC interface.
A Windows program, COMProfibus, and extensive descriptions are
available for the Profibus DP master interface IM308-C. In connection with
the Siemens S5, it is recommended to use the IM308-C because of its
better handling and the possibility of freely assigning peripheral addresses
byte by byte. Versions 2.1 or higher can be considered to be particularly
convenient. An extended type file can be read in with these versions. The
entries in the type file automatically assume the settings for guaranteeing
data consistency. (The figures on the previous pages originate from the
COMProfibus software.)