8
Installing • Commissioning
MODBUS Communication
If an optional RS-232 or RS-485 interface module has been
installed in the controller, MODBUS communication can be run in
parallel with communication via the PROFIBUS-DP interface. --
The necessary communication parameters have to be set by
answering the inquiries of functional block 30 in the device
configuration, dedicated to MODBUS communication.--
Since simultaneous write access via MODBUS communication
and PROFIBUS-DP communication to variables or online
parameters of the devices is possible, the last processed
command enters its value. ---- None of the two communications
has priority over the other. --
In case of cyclic write access to variables via PROFIBUS-DP,
write access via MODBUS communication to the same variable
has no permanent effect. --
It is recommended to avoid cyclic write access to online
parameters, since this would cause various write actions to the
nonvolatile flash memory. --- After around 100,000 write actions
this will lead to malfunctions of the flash EPROM. --
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