User`s guide

64 Agilent VISA User’s Guide
3 Programming with VISA
When you use VI_QUEUE in the mechanism parameter, you are
specifying that the events will be put into a queue. Then, when a
viWaitOnEvent function is invoked, the program execution will
suspend until the enabled event occurs or the timeout period specified is
reached. If the event has already occurred, the viWaitOnEvent function
will return immediately.
Example: Enabling a Hardware Trigger Event This example
illustrates enabling a hardware trigger event.
viEnableEvent(vi, VI_EVENT_TRIG, VI_QUEUE,
VI_NULL);
The VI_QUEUE mechanism specifies that when an event occurs, it will
go into a queue. If you specify VI_ALL_ENABLE_EVENTS in the
eventType parameter, all events that have previously been enabled on
the specified session will be enabled for the mechanism specified in this
function call. Use the viDisableEvent function to stop servicing the
event specified.
Wait on the Event
When using the viWaitOnEvent function, specify the session, the event
type to wait for, and the timeout period to wait:
viWaitOnEvent(vi, inEventType, timeout,
outEventType, outContext);
The event must have previously been enabled with VI_QUEUE
specified as the mechanism parameter.
Table 18 Descriptions of Parameters Used to Enable Events
Parameter Description
vi The session the handler will be installed on.
eventType The type of event to enable.
mechanism The mechanism by which the event will be enabled. Specify
VI_QUEUE to use the queuing method.
context Not used in VISA 1.0. Use VI_NULL.