Chapter 6
– Settings
6.2. System stop prevention
The OB 86 indicates a module error. The OB is necessary to
avoid that the controller turns into Stop condition when short
interruptions in the PROFIBUS communication occur.
In case of errors the inputs are typically set to zero and
should not be evaluated anymore. To save a process image
of the inputs of a PROFIBUS slave before they are reset,
the following method should be applied:
Copy the inputs of a slave cyclically in an array.
When the slave fails the OB 86 will be started.
Set a flag in this OB which prevents further cyclical
copies.
Reset the flag in the OB when the slave is back at the
bus.
Eventually either OB 85 or OB 122 may be started before OB
86 is started. These are called after addressing errors of
failed slaves. Therefore the flag should also be set in these
OBs.
