Data Acquisition Toolbox

Adding Channels to an Analog Output Object

After creating the analog output object, you must add hardware channels to it. As shown by the figure in Adding Channels or Lines, you can think of a device object as a container for channels. The collection of channels contained by the device object is referred to as a channel group. As described in Mapping Hardware Channel IDs to MATLAB Indices, a channel group consists of a mapping between hardware channel IDs and MATLAB indices (see below).

When adding channels to an analog output object, you must follow these rules:

• The channels must reside on the same hardware device. You cannot add channels from different devices, or from different subsystems on the same device.
• The channels must be sampled at the same rate.

You add channels to an analog output object with the addchannel function. addchannel requires the device object and at least one hardware channel ID as input arguments. You can optionally specify MATLAB indices, descriptive channel names, and an output argument. For example, to add two hardware channels to the device object ao created in the preceding section:

• chans = addchannel(ao,0:1);
  

The output argument chans is a channel object that reflects the channel array contained by ao. You can display the class of chans with the whos command.

• whos chans
    Name        Size         Bytes  Class
  
    chans       2x1            512  aochannel object
  
  Grand total is 7 elements using 512 bytes
  

You can use chans to easily access channels. For example, you can easily configure or return property values for one or more channels. As described in Referencing Individual Hardware Channels, you can also access channels with the Channel property.

Once you add channels to an analog output object, the properties listed below are automatically assigned values. These properties provide descriptive information about the channels based on their class type and ID.

Table 6-2: Descriptive Analog Output Channel Properties 

Property Name	Description
HwChannel	Specify the hardware channel ID.
Index	Indicate the MATLAB index of a hardware channel.
Parent	Indicate the parent (device object) of a channel.
Type	Indicate a channel.

You can display the values of these properties for chans with the get function.

• get(chans,{'HwChannel','Index','Parent','Type'})
  ans = 
      [0]    [1]    [1x1 analogoutput]    'Channel'
      [1]    [2]    [1x1 analogoutput]    'Channel'
  

To reference individual channels, you must specify either MATLAB indices or descriptive channel names. Refer to Referencing Individual Hardware Channels for more information.

Creating an Analog Output Object

Configuring Analog Output Properties