Choosing between Express VIs and Low Level VIs (ELVIS RIO Control Toolkit)

LabVIEW 2016 ELVIS RIO Control Toolkit Help

Edition Date: June 2016

Part Number: 376300A-01

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The NI ELVIS RIO Control Toolkit provides the following types of VIs for creating NI ELVIS RIO CM applications:

  • Express VIs—Use the Express VIs to interactively configure the settings for the I/O channels. When you place an Express VI on the block diagram or double-click an Express VI, a configuration dialog box appears. Use this configuration dialog box to configure the Express VI. You can also configure the Express VI by wiring values to the terminals of the Express VI on the block diagram.
  • Low Level VIs—Use the Low Level VIs to have more control over allocating and releasing I/O channels. For example, you can use the Low Level VI to open or close certain channels and change the channel configuration at run time.

Understanding the Underlying Code of Express VIs

In the configuration dialog box of an Express VI, click the View Code tab to view the underlying code of the Express VI. This code consists of the Low Level VIs and other LabVIEW VIs.

The code of the Express VIs uses Smart Open VIs instead of the Open VIs to open references to I/O channels. Smart Open VIs can open an I/O reference the first time they run and then save the reference in memory. The use of Smart Open VIs ensures that the Express VIs can run efficiently in loops because you do not need to open references to I/O channels for each iteration.

You can copy the code of an Express VI to a new block diagram and start programming with the Low Level VIs. After you copy the code, replace the Smart Open VI with an Open VI because the Open VIs open an I/O reference and pass the reference around to all other places where you need to access the I/O channel. You also need to add a Close VI to close I/O references after data operation. The following figure shows an example of modifying the code copied from the Analog Input Express VI.

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Express VIs


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