Table Of Contents

XNET Read (Signal » Waveform) (G Dataflow)

Last Modified: November 2, 2017

Reads data from a session of Signal Input Waveform mode. The data represents a waveform of resampled values for each signal in the session. You can wire the data directly to a LabVIEW Waveform Graph for display.

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session in

The session to read. This session is selected from the LabVIEW project or returned from XNET Create Session. The session mode must be Signal Input Waveform.

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number to read

The number of samples desired. If number to read is positive (or 0), the number of samples returned (size of Y arrays) is no greater than this number. If timeout is nonzero, the number returned is exactly this number on success.

If number to read is negative (typically -1), the maximum number of samples is returned. If number to read is negative, you must use a timeout of zero.

This input is optional. The default value is -1.

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timeout

The time to wait for number to read samples to become available. The timeout is a LabVIEW relative time, represented as 64-bit floating-point in units of seconds.

If timeout is positive, XNET Read (Signal Waveform) waits for number to read samples, then returns that number. If the samples do not arrive prior to the timeout, an error is returned.

If timeout is negative, XNET Read (Signal Waveform) waits indefinitely for number to read samples.

If timeout is zero, XNET Read (Signal Waveform) does not wait and immediately returns all available samples up to the limit number to read specifies.

Because time determines sample availability, typical values for this timeout are 0 (return available) or a large positive value such as 100.0 (wait for a specific number to read). This input is optional. The default value is 0.0.

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error in

Error conditions that occur before this node runs.

The node responds to this input according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Default: No error

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session out

An output that is the same as session in, provided for use with subsequent nodes.

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data

An output that returns a one-dimensional array of LabVIEW waveforms. Each array element corresponds to a signal configured for the session. The order of signals in the array corresponds to the order in the session list.

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t0

The waveform start time. This is a LabVIEW absolute timestamp that specifies the time for the first sample in the Y array.

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dt

The waveform delta time. This is a LabVIEW relative time that specifies the time between each sample in the Y array. LabVIEW relative time is represented as 64-bit floating point in units of seconds. The waveform dt always is the inverse of the XNET Session Resample Rate property.

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Y

The array of resampled signal values. Each signal value is scaled, 64-bit floating point.

The Y array size is the same for all waveforms returned, because it is determined based on time, and not the number of frames received.

If no frame is received for the corresponding signals since you started the session, the XNET Signal Default Value is returned.

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error out

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Where This Node Can Run:

Desktop OS: Windows

FPGA: Supported

Web Server: Not supported in VIs that run in a web application


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