Modular Programming 1.1 2004/06/14 14:51:30 GMT-5 2004/07/16 14:57:00.694 GMT-5 National Instruments certification@ni.com Elizabeth Gregory lizzardg@rice.edu Malan Shiralkar mshiralkar05@hotmail.com Harika Basana ilsai@rice.edu National Instruments certification@ni.com The power of LabVIEW lies in the hierarchical nature of the VI. After you create a VI, you can use it on the block diagram of another VI. There is no limit on the number of layers in the hierarchy. Using modular programming helps you manage changes and debug the block diagram quickly. A VI within another VI is called a subVI. A subVI corresponds to a subroutine in text-based programming languages. When you double-click a subVI, a front panel and block diagram appear, rather than a dialog box in which you can configure options. The front panel includes controls and indicators that might look familiar. The block diagram includes wires, front panel icons, functions, possibly subVIs, and other LabVIEW objects that also might look familiar. The upper right corner of the front panel and block diagram displays the icon for the VI. This icon is the same as the icon that appears when you place the VI on the block diagram.

Icon and Connector Pane After you build a front panel and block diagram, build the icon and the connector pane so you can use the VI as a subVI. Every VI displays an icon, such as the one shown in , in the upper right corner of the front panel and block diagram windows. An icon is a graphical representation of a VI. It can contain text, images, or a combination of both. If you use a VI as a subVI, the icon identifies the subVI on the block diagram of the VI. You can double-click the icon to customize or edit it. You also need to build a connector pane, shown in , to use the VI as a subVI. The connector pane is a set of terminals that correspond to the controls and indicators of that VI, similar to the parameter list of a function call in text-based programming languages. The connector pane defines the inputs and outputs you can wire to the VI so you can use it as a subVI. A connector pane receives data at its input terminals and passes the data to the block diagram code through the front panel controls and receives the results at its output terminals from the front panel indicators. As you create VIs, you might find that you perform a certain operation frequently. Consider using subVIs or loops to perform that operation repetitively. For example, the block diagram in contains two identical operations.

You can create a subVI that performs that operation and call the subVI twice. The example in calls the Temperature VI as a subVI twice on its block diagram and functions the same as the previous block diagram.You also can reuse the subVI in other VIs. Refer to Repetition and Loops for more information about using loops to combine common operations.

Refer to the LabVIEW Basics II: Development Course Manual for more information about application development. The following pseudo-code and block diagrams demonstrate the analogy between subVIs and subroutines. Function Code Calling Program Code main { average (point1, point2, pointavg) } function average (in1, in2, out) { out = (in1 + in2)/2.0; } SubVI Block Diagram CallingVI Block Diagram