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XNET Read (Signal » XY) (G Dataflow)

Last Modified: November 2, 2017

Reads data from a session of Signal Input XY mode.

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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 XY.

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number to read

The number of values desired.

If number to read is positive (or 0), the size of value arrays is no greater than this number.

If number to read is negative (typically -1), the maximum number of values is returned.

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

If number to read values are received for any signal, XNET Read (Signal XY) returns those values, even if the time limit has not occurred. Therefore, to read values up to the time limit, leave number to read unwired (-1).

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time limit

The timestamp to wait for before returning signal values. If time limit is valid, XNET Read (Signal XY) waits for the timestamp to occur, then returns available values (up to number to read). If you increment time limit by a fixed number of seconds for each call to XNET Read (Signal XY), you effectively obtain a moving window of signal values.

If time limit is unwired (invalid), XNET Read (Signal XY) returns immediately all available values up to the current time (up to number to read).

This input is optional. The default value is an invalid timestamp.

The timeout of other XNET Read instances specifies the maximum amount time to wait for a specific number to read values. The time limit of XNET Read (Signal XY) does not specify a worst-case timeout value, but rather a specific absolute timestamp to wait for.

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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 an array of LabVIEW clusters. 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.

Each cluster contains two arrays, one for timestamp and one for value. For each signal, the size of the timestamp and value arrays always is the same, such that it represents a single array of timestamp/value pairs.

Each timestamp/value pair represents a value from a received frame. When signals exist in different frames, the array sizes may be different from one cluster (signal) to another.

When you use this instance with a session of Signal Input Single-Point Mode, time limit and number to read are ignored, and the timestamp and value arrays always contain only one element per signal. This effectively returns a single pair of timestamp and value for every signal.

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timestamp

The array of LabVIEW timestamps, one for each frame received that contains the signal. Each timestamp represents the absolute time when the XNET interface received the frame (end of frame), accurate to microseconds.

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value

The array of signal values, one for each frame received that contains the signal. Each signal value is scaled, 64-bit floating point.

The value array size is the same as the timestamp array size.

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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.

Description

You also can use this instance to read data from a session of Signal Input Single-Point mode, although XNET Read (Signal Single-Point) is more common for that mode.

The data represents an XY plot of timestamp/value pairs for each signal in the session. You can wire the data directly to a LabVIEW XY Graph for display.

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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