Basic Functional Global Variable Example

[Todd S.]

Overview

This VI demonstrates a simple usage of Functional Global Variables in incrementing and displaying a number.

Description

Functional global variables are VIs that use loops with uninitialized shift registers to hold global data. A functional global variable usually has an action input parameter that specifies which task the VI performs.

The VI uses an uninitialized shift register in a While Loop to hold the result of the operation. The following illustration shows a functional global variable that implements a simple count global variable. The actions in this example are initialize, read, increment, and decrement.

Every time you call the VI (Call Functional Global.vi), the block diagram in the loop runs exactly once. Depending on the action parameter, the case inside the loop initializes, does not change, incrementally increases, or incrementally decreases the value of the shift register.  Although you can use functional global variables to implement simple global variables, they are especially useful when implementing more complex data structures, such as a stack or a queue buffer. You also can use functional global variables to protect access to global resources, such as files, instruments, and data acquisition devices, that you cannot represent with a global variable.

Requirements

LabVIEW 2012 (or compatible)

Steps to Implement or Execute Code

To make this example work with your code, or as a standalone application:

1. Download the attached folder
2. Open the "Functional Global Variable_LV2012_NI Verified.lvproj" Project
3. Open the Call Functional Global Variable.vi
4. Run the VI
5. Initialize the value of the variable in the "Initialize to" control
6. Click on Initialize to store the value in the buffer
7. Click on Increment to Update the value in the buffer
8. Click on Get to display the value stored in the buffer

Additional Information or References

FVG used a SubVI

 Block Diagram of FGV

**This document has been updated to meet the current required format for the NI Code Exchange.**