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.
List of mappings of functions to call to events with: Name, Description, Function to call, and Active (enable or disable the configuration)

Table 66. 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 need 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 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 line.

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 with an online 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 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 (`Exit`) all tasks.	Runtime main loop	No