VISA Wait on Event Function

LabVIEW 2017 Help

Edition Date: March 2017

Part Number: 371361P-01

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Owning Palette: Event Handling VIs and Functions

Requires: Base Development System

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 specifies the time, in milliseconds, that the function waits for the event.
VISA resource name specifies the resource to be opened. The VISA resource name control also specifies the session and class.
event type is the logical event identifier. You can select from the following VISA event types.

Service Request0x3FFF200B
VXI Signal0x3FFF2020
VXI/VME Interrupt0xBFFF2021
VXI/VME Sysfail0x3FFF201D
VXI/VME Sysreset0x3FFF201E
GPIB Talk0x3FFF2013
GPIB Listen0x3FFF2014
PXI Interrupt0x3FFF2022
Serial Break0x3FFF2023
Serial TermChar0x3FFF2024
Serial CTS0x3FFF2029
Serial DSR0x3FFF202A
Serial DCD0x3FFF202C
Serial RI0x3FFF202E
Serial Character0x3FFF2035
USB Interrupt0x3FFF2037
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 node runs. This input provides standard error in functionality.
VISA resource name out is a copy of the VISA resource name that VISA functions return.
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. This output provides standard error out functionality.

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.


Refer to the Detect Serial Break Event VI in the labview\examples\Instrument IO\Serial directory for an example of using the VISA Wait on Event function.


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