The ViSession handle that you obtain from Ivi_SpecificDriverNew. The handle identifies a particular IVI session.

Pass the ID of an attribute for this parameter.

The include file for a specific instrument driver defines constant names for all of the user-accessible attributes that apply to the driver. This includes attributes that the IVI engine defines, attributes that the instrument class defines, and attributes that are specific to the particular instrument. Each defined constant name begins with PREFIX_ATTR_, where PREFIX is the specific instrument prefix.

For each IVI engine attribute, the specific driver include file uses the same constant name that appears in ivi.h, except that the specific instrument prefix replaces the IVI prefix. For example, ivi.h defines IVI_ATTR_CACHE, and the Fluke 45 include file, fl45.h, defines the following constant name:

#define FL45_ATTR_CACHE  IVI_ATTR_CACHE

For each instrument class attribute, the specific driver include file uses the same constant name that appears in the instrument class include file, except that the specific instrument prefix replaces the class prefix. For example, the DMM class include file, ividmm.h, defines IVIDMM_ATTR_RANGE, and fl45.h defines the following constant name:

#define FL45_ATTR_RANGE  IVIDMM_ATTR_RANGE

For each specific instrument attribute, the specific driver include file defines a constant name and assigns a value that is an offset from IVI_SPECIFIC_PUBLIC_ATTR_BASE. For example, fl45.h defines the following constant name:

#define FL45_ATTR_HOLD_THRESHOLD \ (IVI_SPECIFIC_PUBLIC_ATTR_BASE + 3L)

For each attribute that is private to an instrument driver, the instrument driver source file defines a constant name and assigns a value that is an offset from IVI_SPECIFIC_PRIVATE_ATTR_BASE. For example, hp34401a.c defines the following constant name:

#define HP34401A_ATTR_TRIGGER_TYPE \ (IVI_SPECIFIC_PRIVATE_ATTR_BASE + 1L)

Specify the read callback function you want the IVI engine to invoke when you request the current value of the attribute.

You must define the read callback function in the source code for the specific instrument driver. The function must have the following prototype:

ViStatus _VI_FUNC Callback(ViSession vi,ViSession io,
ViConstString repCapName,
ViAttr attributeId,
const ViConstString cacheValue);

Unlike the read callback functions for the other data types, you do not return the current value to the caller through the last parameter. Instead, you return the current value by passing it to Ivi_SetValInStringCallback in the callback function.

Note  If you want to use the Edit IVI Specific Driver Attributes dialog box to develop your instrument driver source code, retain the parameter names as shown in the prototype for the callback.

If you do not want to use a read callback function, pass VI_NULL.