Extension Groups
Extension groups contain specialized groups of functions and attributes that are common to many instruments in that class, but not all. The IVI specifications do not require specific instrument drivers to implement extension groups. With extension groups, the IVI class drivers create standard programming interfaces for features and capabilities that are not common to every instrument of that class.
For example, although all oscilloscopes have similar base capabilities for vertical and horizontal settings, they have a wide variety of trigger modes. The IviScope class driver includes extensions for different trigger modes, such as TV trigger, runt trigger, width trigger, and so on. Every oscilloscope that has TV triggering can comply with the TV trigger extension group functions and attributes of the IviScope class. However, an oscilloscope that does not support the TV trigger extension group can still comply with the IviScope class because the oscilloscope can support the base capabilities of the IviScope class.
If you use an extension group in your program, any instrument you use with the program must support the extension group. The LabWindows/CVI function panels, LabVIEW VIs, and help file for the class drivers mark functions and attributes that are a part of an extension group with a special symbol. For example, the IviScope class driver help file marks the functions and attributes that control the TV trigger extension group with the symbol [TV]. For more information about the extension groups of a particular class, refer to: