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Owning Palette: Event Handling VIs and Functions

Installed With: Base Package

Suspends execution of an application thread and waits for an event type for a time period not to exceed that specified by timeout.

Details  Example

	timeout is the period of time in milliseconds to wait for the event.
	VISA resource name specifies the resource to be opened. This control also specifies the session and class. Refer to VISA Resource Name Control for more information.
	event type is the logical event identifier. You can select from the following VISA event types. Service Request 0x3FFF200B Trigger 0xBFFF200A Clear 0x3FFF200D VXI Signal 0x3FFF2020 VXI/VME Interrupt 0xBFFF2021 VXI/VME Sysfail 0x3FFF201D VXI/VME Sysreset 0x3FFF201E GPIB CIC 0x3FFF2012 GPIB Talk 0x3FFF2013 GPIB Listen 0x3FFF2014 PXI Interrupt 0x3FFF2022 Serial Break 0x3FFF2023 Serial TermChar 0x3FFF2024 Serial CTS 0x3FFF2029 Serial DSR 0x3FFF202A Serial DCD 0x3FFF202C Serial RI 0x3FFF202E Serial Character 0x3FFF2035 USB Interrupt 0x3FFF2037 All Enabled (default) 0x3FFF7FFF Refer to the NI-VISA Help for more information about event types.
	event class specifies the class of event for which the function waits. The default is Generic Event, meaning the function recognizes any class of event.
	error in describes error conditions that occur before this VI or function runs. The default is no error. If an error occurred before this VI or function runs, the VI or function passes the error in value to error out. This VI or function runs normally only if no error occurred before this VI or function runs. If an error occurs while this VI or function runs, it runs normally and sets its own error status in error out. Use the Simple Error Handler or General Error Handler VIs to display the description of the error code. Use exception control to treat what is normally an error as no error or to treat a warning as an error. Use error in and error out to check errors and to specify execution order by wiring error out from one node to error in of the next node. status is TRUE (X) if an error occurred before this VI or function ran or FALSE (checkmark) to indicate a warning or that no error occurred before this VI or function ran. The default is FALSE. code is the error or warning code. The default is 0. If status is TRUE, code is a nonzero error code. If status is FALSE, code is 0 or a warning code. source specifies the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning. The default is an empty string.
	VISA resource name out is a copy of the VISA resource name that VISA functions return. Refer to VISA Resource Name Control for more information.
	event type out identifies the event type received if the wait was successful.
	event is valid if the wait was successful. Wire event to a Property Node to get further information about the event. Wire event to the VISA Close function when examination of the event is complete.
	error out contains error information. If error in indicates that an error occurred before this VI or function ran, error out contains the same error information. Otherwise, it describes the error status that this VI or function produces. Right-click the error out front panel indicator and select Explain Error from the shortcut menu for more information about the error. status is TRUE (X) if an error occurred or FALSE (checkmark) to indicate a warning or that no error occurred. code is the error or warning code. If status is TRUE, code is a nonzero error code. If status is FALSE, code is 0 or a warning code. source describes the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning.

VISA Wait on Event Details

You can set this function to perform I/O operations synchronously or asynchronously. By default, the function handles I/O operations asynchronously. Right-click the function and select Synchronous I/O Mode»Synchronous from the shortcut menu to synchronously wait for an occurrence of the specified event.

Note  In most applications, synchronous calls are slightly faster when you are communicating with 4 or fewer instruments. Asynchronous operations result in a significantly faster application when you are communicating with 5 or more instruments. The LabVIEW default is asynchronous I/O.

Refer to individual event descriptions for context definitions. If the specified event type is All Events (0x3FFF7FFF), the operation waits for any event that is enabled for the given session.

Note  You must call the VISA Enable Event function for a given session before using the VISA Wait on Event function.

If a session's event queue becomes full and a new event arrives, the new event is discarded. The default event queue size per session is 50. If you expect more than 50 unhandled events to arrive, you can use the General Settings:Maximum Queue Length property to set event queue size programmatically.

Example

Refer to the Detect Break Event VI in the labview\examples\instr\smplserl.llb for an example of using the VISA Wait on Event function.