Fetch Bus Waveform (WDT)
- Updated2023-02-17
- 4 minute(s) read
Fetch Bus Waveform (WDT)
Fetches an array of data using the waveform data type and returns an array of waveforms, one for each element in the channel list array.
This node allows you to fetch data in any order or subset that you desire without the need to manipulate the data after fetching it.
Inputs/Outputs
timestamp type
Parameter that specifies whether the timestamp for the waveform data is relative or absolute.
channel list
channel list specifies the channels from which to fetch waveform data. You must assign all channels that you want to fetch using the Assign Dynamic Channelsnode before selecting those channels with this parameter.
NI-HSDIO fetches waveform data in the order that you list channels in this parameter, not in the order that those channels are listed in the Assign Dynamic Channelsnode. If you leave this parameter blank, NI-HSDIO fetches all channels.
Each element in this array, consisting of its specified channels, is output as a single waveform in the data parameter. Specify multiple channels in each element by using a channel list or a channel range. A channel list is a comma (,) separated sequence of channel names (for example, 0,2 specifies a waveform showing channels 0 and 2). A channel range is a lower bound channel followed by a hyphen (-) or colon (:) followed by an upper bound channel (for example, 0-2 specifies a waveform showing channels 0, 1, and 2).
You can include the same channel in multiple elements of this array. For example, if you choose 0:2 as the first element, 0, 2 as the second element, and 0 as the third element, the data parameter returns three waveforms: the first depicting channels 0 through 2, the second depicting channels 0 and 2, and the third depicting just channel 0.
session in
Instrument session obtained from the Initialize Acquisition Sessionnode, the Initialize Generation Sessionnode, or the Initialize External Calibrationnode.
error in
Error conditions that occur before this node runs.
The node responds to this input according to standard error behavior.
Default value: No error
samples to read
The specified number of samples to fetch per waveform.
If you specify a value for samples to read that is greater than the number of samples in the device memory, NI-HSDIO returns the samples that are acquired after max time milliseconds. Setting this parameter to -1 acquires the samples per record specified in the niHSDIO Configure Acquisition Sizenode.
maximum time (ms)
The time, in milliseconds, allotted for the node to complete before NI-HSDIO returns a timeout error.
If you set the value to -1, the node never times out. If you set this parameter to 0, the node returns immediately with up to the number of samples specified in samples to read.
If samples to read is greater than the number of samples in the device memory and all the available samples are acquired before a timeout, NI-HSDIO returns the available samples.
Default value: 10000
starting record
The record at which you want to start fetching data.
Default value: 0
session out
Handle that identifies the session in all subsequent node calls.
The session out parameter is obtained from the Initialize Acquisition Sessionnode or the Initialize Generation Sessionnode.
error out
Error information.
The node produces this output according to standard error behavior.
data
The acquired data as an array of waveforms, one for each element in the channel list parameter.
number of samples read
The number of samples that were successfully acquired and transferred into data.