Data Acquisition Toolbox

Logging or Sending Data

While the device object is running, you can

• Log data acquired from an analog input subsystem to the engine (memory) or to a disk file.
• Output data queued in the engine to an analog output subsystem.

However, before you can log or send data, a trigger must occur. You configure an analog input or analog output trigger with the TriggerType property. All the examples presented in this section use the default TriggerType value of Immediate, which executes the trigger immediately after the start function is issued. For a detailed description of triggers, refer to Configuring Analog Input Triggers or Configuring Analog Output Triggers.

Extracting Logged Data

When a trigger occurs for an analog input object, the Logging property is automatically set to On and data acquired from the hardware is logged to the engine or a disk file. You extract logged data from the engine with the getdata function. For example, to extract 500 samples for each channel contained by ai,

• data = getdata(ai,500);
  

getdata blocks the MATLAB command line until all the requested data is returned to the workspace. You can extract data any time after the trigger occurs.

Sending Queued Data

For analog output objects, you must queue data in the engine with the putdata function before it can be output to the hardware. For example, to queue 8000 samples in the engine for each channel contained by the analog output object ao

• ao = analogoutput('winsound');
  addchannel(ao,1:2);
  data = sin(linspace(0,2*pi*500,8000))';
  putdata(ao,[data data])
  

Before the queued data can be output, you must start the analog output object.

• start(ao)
  

When a trigger occurs, the Sending property is automatically set to On and the queued data is sent to the hardware.

Starting the Device Object

Stopping the Device Object