Data Acquisition Toolbox

Event Types

The analog output event types and associated callback properties are described below.

Table 6-9: Analog Output Callback Properties  

Event Type	Property Name
Run-time error	RuntimeErrorFcn
Samples output	SamplesOutputFcn
	SamplesOutputFcnCount
Start	StartFcn
Stop	StopFcn
Timer	TimerFcn
	TimerPeriod
Trigger	TriggerFcn

Run-time Error Event.   A run-time error event is generated immediately after a run-time error occurs. This event executes the callback function specified for RuntimeErrorFcn. Additionally, a toolbox error message is automatically displayed to the MATLAB workspace. If an error occurs that is not explicitly handled by the toolbox, then the hardware-specific error message is displayed.

The default value for RunTimeErrorFcn is daqcallback, which displays the event type, the time the event occurred, the device object name, and the error message.

Run-time errors include hardware errors and timeouts. Run-time errors do not include configuration errors such as setting an invalid property value.

Samples Output Event.   A samples output event is generated immediately after the number of samples specified by the SamplesOutputFcnCount property is output for each channel group member. This event executes the callback function specified for SamplesOutputFcn.

Start Event.   A start event is generated immediately after the start function is issued. This event executes the callback function specified for StartFcn. When the callback function has finished executing, Running is automatically set to On and the device object and hardware device begin executing. The device object is not started if an error occurs while executing the callback function.

Stop Event.   A stop event is generated immediately after the device object and hardware device stop running. This occurs when

• The stop function is issued.
• The requested number of samples is output.
• A run-time error occurs.

A stop event executes the callback function specified for StopFcn. Under most circumstances, the callback function is not guaranteed to complete execution until sometime after the device object and hardware device stop running, and the Running property is set to Off.

Timer Event.   A timer event is generated whenever the time specified by the TimerPeriod property passes. This event executes the callback function specified for TimerFcn. Time is measured relative to when the device object starts running.

Some timer events might not be processed if your system is significantly slowed or if the TimerPeriod value is too small. For example, a common application for timer events is to display data. However, because displaying data is a CPU-intensive task, some of these events might be dropped. To guarantee that events are not dropped, you can use the SamplesOutputFcn property.

Trigger Event.   A trigger event is generated immediately after a trigger occurs. This event executes the callback function specified for TriggerFcn. Under most circumstances, the callback function is not guaranteed to complete execution until sometime after Sending is set to On.

Events and Callbacks

Recording and Retrieving Event Information