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Set Named Waveform Next Write Position (G Dataflow)

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    Last Modified: September 27, 2017

    Modifies where to next write within a named waveform.

    The Write Named Waveform node always begins writing at the current write position. Existing data in the waveform is overwritten.

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    session in

    Instrument session obtained from the Initialize Acquisition Session node, the Initialize Generation Session node, or the Initialize External Calibration node.

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    waveform name

    The name you want to associate with the allocated waveform memory.

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    position

    Parameter that specifies where to place the write position, in conjunction with offset.

    Name Value Description
    Current Write Position The offset is relative to the current write position in the waveform.
    Start of Waveform The offset is relative to the beginning of the waveform.
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    offset

    The specified offset for the write position within the named waveform. offset is in samples.

    Before issuing a write waveform command, the offset relative to the start of the waveform must be a multiple of 32 samples for PXI/PXIe-654x/655x devices (64 samples for the PXI/PXIe-6547/6548 in DDR mode) and a multiple of 64 samples for PXI/PXIe-656x devices (128 samples for the PXI/PXIe-656x is in DDR mode).

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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

    Handle that identifies the session in all subsequent node calls.

    The session out parameter is obtained from the Initialize Acquisition Session node or the Initialize Generation Session node.

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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.

    Using the position and offset parameters

    position and offset are used together to determine the next write position. position describes an absolute or relative move. offset is the number of samples to shift the next write position. You must always set the write position at a position that is a multiple of 32 samples for PXI/PXIe-654x/655x devices (64 samples for the PXI/PXIe-6547/6548 in DDR mode) or a multiple of 64 samples for PXI/PXIe-656x devices (128 samples for the PXI/PXIe-656x in DDR mode).

    The following table shows examples of combinations of position and offset.

    Position Offset Next Write Position
    Start of Waveform 0 Start of Waveform
    Start of Waveform 5 Sixth sample of waveform
    Start of Waveform -1 ERROR. These settings would try to place write position before start of waveform.
    Current Write Position 0 No effect. These settings leave the next write position unchanged.
    Current Write Position 10 Shift write position 10 samples ahead from current location. This position setting is valid only if the current write position plus this offset is in the waveform.
    Current Write Position -10 Shift write position 10 samples back from current location. This position setting is valid only if the current write position is greater than 10.

    The write position is moved to the end of the most recently written data after each use of the Write Named Waveform node. Thus you do not need to explicitly use the Set Named Waveform Next Write Position node. Setting the position beyond the bounds of the allocated space produces an error.

    Where This Node Can Run:

    Desktop OS: Windows

    FPGA: Not supported

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


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