Getting Started With Analog Input (Data Acquisition Toolbox)

Data Acquisition Toolbox

Getting Function and Property Help

You can access help on Data Acquisition Toolbox functions and properties using some or all of these resources:

The reference sections in this book
M-file help
HTML-based property help available through the Help Desk
The daqhelp function
The propinfo function

The daqhelp and propinfo functions are discussed below.

The daqhelp function

daqhelp can be used to display information for both functions and properties. daqhelp can also be used to display information about device objects and constructors. A device object need not exist for you to obtain this information. For example, before creating a device object, the command

daqhelp analoginput/peekdata

displays the M-file help for analoginput/peekdata, while the command

daqhelp analoginput.TriggerDelayUnits

displays the help for the analog input property named TriggerDelayUnits. After creating a device object, you can display all the associated help by specifying the device object name as an argument to daqhelp. For example, to display all the associated help for the sound card example on page 3-17:

daqhelp(AI)

The commands listed below are some of the ways daqhelp can be used to display help for specific functions and properties for AI.

daqhelp(AI, 'TriggerDelayUnits');
daqhelp(AI, 'getdata');
daqhelp(AI, 'set');

For more information about daqhelp, refer to Chapter 6, "Function Reference."

The propinfo function

propinfo returns information about device object or channel properties. The information is returned as a structure containing the fields shown below.


Property	Description
`Type`	The property data type (e.g., double, string)
`Constraint`	Constraints on property values (e.g., none, bounded)
`ConstraintValue`	Property value constraint (e.g., range of valid values, elements of an enumerated list)
`DefaultValue`	The property default value
`ReadOnly`	If a property is read-only, a "1" is returned. Otherwise a "0" is returned.
`ReadOnlyRunning`	If a property cannot be set while the device object is running, a "1" is returned. Otherwise a "0" is returned.
`DeviceSpecific`	If the property is device-specific, then a "1" is returned. Otherwise a "0" is returned.

This information can be used simply to evaluate the allowed value(s) for a given property, or to programmatically configure property values. For example, the following command displays all the propinfo field values for the SampleRate property for the sound card example on page 3-17.

info = propinfo(AI);
info.SampleRate
ans = 
               Type: 'double'
         Constraint: 'Bounded'
    ConstraintValue: [8000 44100]
       DefaultValue: 8000
           ReadOnly: 0
    ReadOnlyRunning: 1
     DeviceSpecific: 0

To display the data type of the InputRange property:

info1 = propinfo(AI.Channel);
info1.InputRange.Type
ans =
double array

For more information about propinfo, refer to Chapter 6, "Function Reference."

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