Tab 'System Events'

Object: “Task Configuration”

On the “System Events” tab, you define which event calls which function and whether or not the configuration is currently activated. You use this tab when a system event (instead of a task) should call a project function.

“Add Event Handler”	Opens the “Add Event Handler” dialog
“Remove Event Handler”	Deletes the selected list assignment
“Event Info”	Shows information from the corresponding event library
“Open Event Function”	Opens the editor of the new function for the selected assignment You have selected the implementation language of the new function in the “Add Event Handler” dialog.
Assignment of functions to call for events with: “Name”,“Description”, “Function to call”, and “Active” (activate/deactivate configuration).

Table 486: “Add Event Handler”
Adds a new assignment "Event – Function to call" to the list
“Event”	The possible selection depends on the target device. CODESYS marks unavailable events with a red symbol in front of the name. A list of all possible system events is located at the end of this section.
“Function to call”	Function name (“POU”, type “FUNCTION”) You have to specify the name of the new function. CODESYS inserts the function to the device tree after you confirm the dialog.
“Scope”	“Application”: The function is available to the application. “POUs”: The function is available to the entire project.
“Implementation language”	Implementation language for the new function
“Description”	Short description of the selected event

Features in “Online Mode”

The list of assignments from called functions to events also includes the following information: “Event Status”, “Call Count”, and the “Online Reset” button.

“Event Status”

‎0‎: No error has occurred.

Does not equal ‎0‎: Error. You need to consult the respective runtime system documentation.

“Call Count”

Displays how often the event has occurred or the associated function has been called.

“Online Reset”

CODESYS reinitializes the event lists and resets the counter for the events/function calls. Incorrectly initialized events are displayed with a red status cell.

Possible system events

Event	Description	Task	Debugging
PrepareStart	Call before starting the application	Communication task	No
StartDone	Call after starting the application	Communication task	No
PrepareStop	Call before stopping the application	Communication task	No
StopDone	Call after stopping the application	Communication task	No
PrepareReset	Call before resetting the application	Communication task	No
ResetDone	Call after resetting the application	Communication task	No
PrepareOnlineChange	Call before online change of the application	Communication task	No
OnlineChangeDone	Call after online change of the application	Communication task	No
PrepareDownload	Call before downloading the application	Communication task	No
DownloadDone	Call after downloading the application	Communication task	No
PrepareDelete	Call before deleting the application	Communication task	No
DeleteDone	Call after deleting the application	Communication task	No
PrepareExit	Call before exiting the application	Communication task	No
ExitDone	Call after exiting the application	Communication task	No
CodeInitDone	Event is sent after Code Init. Called within the task safe section and only for an online change change (for example, the copy code for online change is executed here).	Communication task	No
Exception	The event is sent if an exception has occurred in the context of an application.	Exception handling task of the runtime, or the task itself if the runtime does not support exception handling	Depends on the task
Login	Login of a client to this application	Communication task	No
Logout	Logout of a client from this application	Communication task	No
BeforeReadingInputs	Call before reading the inputs	IEC task	Yes
AfterReadingInputs	Call after reading the inputs	IEC task	Yes
BeforeWritingOutputs	Call before writing the outputs	IEC task	Yes
AfterWritingOutputs	Call after writing the outputs	IEC task	Yes
DebugLoop	Event is sent in cycles to the debug loop if the IEC task stops at a breakpoint.	Communication task	No
PrepareShutdown	Event is sent immediately before the runtime system is downloaded.	Runtime main loop	No
PrepareExitComm	Event is sent during download before exiting the communication server.	Runtime main loop	No
PrepareExitTasks	Event is sent during download before exiting all tasks.	Runtime main loop	No