Value Has Changed PtByPt VI

Owning Palette: Other Functions PtByPt VIs

Requires: Full Development System

Detects changes of input data point between the current call and the previous call to the Value Has Changed PtByPt VI.

Note  By default, reentrant execution is enabled in all Point By Point VIs.

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	initialize, when TRUE, initializes the internal state of the VI.
	input data point is an input data point.
	has changed becomes TRUE when the value changes.
	output data point is a copy of input data point.

Value Has Changed PtByPt Details

You can use the Value Has Changed PtByPt VI to trigger events when a user changes an input parameter. The Boolean indicator has changed becomes TRUE when the change of input data point occurs.

The following programming sequence describes how to use the Value Has Changed PtByPt VI to build a point-by-point error checking mechanism for Point By Point VIs that have an error parameter.

1. Choose a parameter that you want to monitor closely for errors.
2. Wire the parameter value as input data point to the Value Has Changed PtByPt VI.
3. Transfer the output data point, which is always the unchanged input data point in the Value Has Changed PtByPt VI, to the target VI.
4. Pass the TRUE event generated by the Value Has Changed PtByPt VI to the target VI to trigger initialization. The Value Has Changed PtByPt VI outputs a TRUE value whenever the input parameter value changes.

For the first call that follows initialization of the target VI, LabVIEW checks for errors. Initialization of the target VI and error checking occurs every time the input parameter changes.