Applies To:
  • CitectSCADA 4.20 Service Pack A, 5.41

This KB article is mainly for driver developers or customers experiencing crashes at Citect shutdown.

In Citect, a driver's StopUnit is called at Citect shutdown to release resources allocated for that unit.

The StopUnit is called if the unit is online, at shutdown or when a unit is disabled. Thus it is possible that a unit will NOT get a StopUnit when the unit is offline. This can cause Citect crashes as these resources have not been released.


To force Citect to always call the StopUnit, then set


Now the StopUnit is always called provided an InitUnit occurred at some stage prior.

Note: if the InitChannel call had failed, then the units belonging to that port will not have their InitUnits called. As a consequence, a StopUnit will not occur in this instance.

Note: there are many reasons for crashes at shutdown, so this setting may not resolve your issue.

This setting will also ensure that any PC services used by the driver, can be notified of the shutdown.