Data Acquisition Toolbox™

peekdata - Preview most recent acquired data

Syntax

data = peekdata(obj,samples)
data = peekdata(obj,samples,'type')

Arguments

`obj`	An analog input object.
`samples`	The number of samples to preview for each channel contained by `obj`.
`'``type``'`	Specifies the format of the extracted data as `double` (the default) or as `native`.
`data`	An m-by-n matrix where m is the number of samples and n is the number of channels.

Description

data = peekdata(obj,samples) returns the latest number of samples specified by samples to data.

data = peekdata(obj,samples,'type') returns the number of samples specified by samples in the format specified by type for each channel contained by obj. If type is specified as native, the data is returned in the native data format of the device. If type is specified as double (the default), the data is returned as doubles.

Remarks

More About Using peekdata

Unlike getdata, peekdata is a nonblocking function that immediately returns control to the MATLAB^® workspace. Because peekdata does not block execution control, data might be missed or repeated.
peekdata takes a "snapshot" of the most recent acquired data and does not remove samples from the data acquisition engine. Therefore, the SamplesAvailable property value is not affected when peekdata is called.

Rules for Using peekdata

You can call peekdata before a trigger executes. Therefore, peekdata is useful for previewing data before it is logged to the engine or to a disk file.
In most cases, you will call peekdata while the device object is running. However, you can call peekdata once after the device object stops running.
If samples is greater than the number of samples currently acquired, all available samples are returned with a warning message stating that the requested number of samples were not available.

Examples

Create the analog input object ai for a National Instruments^® board, add eight input channels, and configure ai for a two-second acquisition.

ai = analoginput('nidaq','Dev1');
addchannel(ai,0:7);
set(ai,'SampleRate',2000)
set(ai,'SamplesPerTrigger',4000)

After issuing the start function, you can preview the data.

start(ai)
data = peekdata(ai,100);

peekdata returns 100 samples to data for all eight channel group members. If 100 samples are not available, then whatever samples are available will be returned and a warning message is issued. The data is not removed from the data acquisition engine.