Siemens SIMATIC ET 200AL System Manual page 1276

Cyclical distribution of the bus parameters
If the check box "Activate cyclical distribution of bus parameters" is selected under "Bus
parameters" with the selected PROFIBUS subnet in the Inspector window, the bus
parameters are sent cyclically during operation by the modules that support this function.
This way you can, for example, connect a programming device to the PROFIBUS during
operation.
Disable this function in the following cases:
● In constant bus cycle time mode to minimize the bus cycle.
● If third-party devices are connected in the PROFIBUS subnet whose protocol uses the
DSAP 63 (Destination Service Access Point) for multicast.
Figure 3-6 Bus parameters
PROFIBUS with STEP 7 V13
Function Manual, 12/2014, A5E03775446-AC
Parameter assignment/addressing
3.6 Bus parameters
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