Data Acquisition Toolbox

Saving and Loading Device Objects

You can save a device object to disk using two possible formats:

• As an M-file using the obj2mfile function
• As a MAT-file using the save command

For analog input objects, you can also save acquired data, hardware information, and so on to a log file. Refer to Logging Information to Disk for more information.

Saving Device Objects to an M-File

You can save a device object to an M-file using the obj2mfile function. obj2mfile provides you with these options:

• Save all property values, or save only those property values that differ from their default values.

• Read-only property values are not saved. Therefore, read-only properties use their default values when you load the device object into the MATLAB workspace. To determine if a property is read-only, use the propinfo function or examine the property reference pages.

• Save property values using the set syntax, the dot notation, or named referencing (if defined).

• If the UserData property is not empty, or if a callback property is set to a cell array of values or a function handle, then the data stored in these properties is written to a MAT-file when the device object is saved. The MAT-file has the same name as the M-file containing the device object code.

For example, suppose you create the analog input object ai for a sound card, add two channels to it, and configure several property values.

• ai = analoginput('winsound');
  addchannel(ai,1:2,{'Temp1';'Temp2'}); 
  time = now;
  set(ai,'SampleRate',11025,'TriggerRepeat',4)
  set(ai,'TriggerFcn',{@mycallback,time})
  start(ai)
  

The following command saves ai and the modified property values to the M-file myai.m. Because the TriggerFcn property is set to a cell array of values, its value is automatically written to the MAT-file myai.mat.

• obj2mfile(ai,'myai.m');
  
  Created: d:\v6\myfiles\myai.m
  Created: d:\v6\myfiles\myai.mat
  

Use the type command to display myai.m at the command line.

Loading the Device Object

To load a device object that was saved as an M-file into the MATLAB workspace, type the name of the M-file at the command line. For example, to load ai from the M-file myai.m:

• ai = myai
  

Note that the read-only properties such as SamplesAcquired and SamplesAvailable are restored to their default values.

• get(ai,{'SamplesAcquired','SamplesAvailable'})
  ans = 
      [0]    [0]
  

When loading ai into the workspace, the MAT-file myai.mat is automatically loaded and the TriggerFcn property value is restored.

• ai.TriggerFcn
  ans = 
      [@mycallback]    [7.3071e+005]
  

Saving and Loading the Session

Saving Device Objects to a MAT-File