User`s guide

8 Using Events and Callbacks

8-10

Data Fields for Timer Events

For timer events, the Data structure contains these fields.

Field Name Description

AbsTime Absolute time the event occurred, returned in MATLAB clock

format

[year month day hour minute seconds]

FrameMemoryLimit Amount of memory allotted for frame storage. You can specify

this value using the imaqmem function.

FrameMemoryUsed Amount of frame memory that is currently in use

Accessing Data in the Event Log

While a video input object is running, the toolbox stores event information in the object's

EventLog property. The value of this property is an array of event structures. Each

structure represents one event. For detailed information about the composition of an

event structure for each type of event, see “Event Structures” on page 8-8.

The toolbox adds event structures to the EventLog array in the order in which the

events occur. The first event structure reflects the first event recorded, the second event

structure reflects the second event recorded, and so on.

Note Only start, stop, error, and trigger events are recorded in the EventLog property.

Frames-acquired events and timer events are not included in the EventLog. Event

structures for these events (and all the other events) are available to callback functions.

For more information, see “Creating and Executing Callback Functions” on page 8-12.

To illustrate the event log, this example creates a video input object, runs it, and then

examines the object's EventLog property:

Create an image acquisition object — This example creates a video input object

for a Matrox image acquisition device. To run this example on your system, use the

imaqhwinfo function to get the object constructor for your image acquisition device

and substitute that syntax for the following code.

vid = videoinput('matrox',1);