Measurement Computing UL for NI LabVIEW - Manual (Page 15)

How to use the
NI LabVIEW Extensions (VIs) UL Extension VI example programs
UL function contexts: foreground (__Fg) and background (__Bg)
There are two distinct VIs for every UL function featuring background operation. One is for foreground
operation only, and the other is for background operation only. The last two letters of the function names are
"Fg" and "Bg" for foreground and background, respectively. Their parameter lists differ, in that background
VIs have a
Context output that must be wired to subsequent VIs (GetStatus.VI and StopBg.VI).
Context is an output data structure that contains information such as the board number, the data array, the size
of the data array, the initial status of the operation, and the error code. Connecting a probe to the Context wire
displays the elements in the data structure. You can check the intermediate values if desired. In general, the
background VIs should conform to the wiring pattern shown in Figure 1. There are several example programs
that effectively demonstrate the correct wiring and use of Contexts. Please refer to example VIs whose names
end in "BG."
Figure 1. Background VIs General Wiring Pattern
UL Extension VI example programs
The UL for LabVIEW software package includes example programs which demonstrate how to use the
Universal Library low-level extension VIs. We strongly suggest that you review the example programs to help
you understand how to integrate the VIs into your program. The following example programs are included to
demonstrate the LabVIEW interface:
Example VI explanation
XAIN Single analog input in a while loop with a metered display.
XAINSCBG Analog input scan in the background. Display data on a graph. Uses GetStatus.VI,
StopBg.VI and OptAIn.VI.
XAICNBG Analog input scan in the background in the CONTINUOUS mode. Same as
XAINSCBG but runs continuously displaying data in real time.
XAINSCFG Analog input scan in the foreground. Displays data on a graph. Uses SelChan.VI
and OptAIn.VI.
XAIOSCB Demonstrates concurrent analog input and output scans.
XAOUT Single analog output. Demonstrates sequences, case statements, for loops, and
while loops.
XAOUTSCB Analog output scan in the background. Uses GetStatus.VI and StopBg.VI.
XAOUTSCF Analog output scan in the foreground. Generates sinusoidal data.
XAPRETRB Analog pre-trigger in the background. Display data on a graph. Uses GetStatus.VI,
StopBg.VI and ACnvPrDt.VI.
XAPRETRF Analog pre-trigger in the foreground. Displays data on a graph. Uses SelChan.VI
and ACnvPrDt.VI.
XASCFILE Analog input to a file. Displays data on a graph. Uses FileAInS.VI and
FileRead.VI.
XASCMEM Analog input to memory board. Displays data on a graph. Uses MemReset.VI and
MemRead.VI.
XCFREQ Displays frequency of signal at counter input. Uses C9513Init.VI and CFreqIn.VI.
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