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ManualsBrandsDAQ ManualsAmplifierVXI-SC-1102

Chapter 3 Software Overview

However, if the information provided by

DAQ_Check

is not sufficient,

DAQ_Monitor

or the double-buffered functions might be a better choice.

With

DAQ_Monitor

, not only can you monitor the data acquisition

process, but you can also retrieve a portion of the acquired data. With the

double-buffered functions, you can retrieve half of the data buffer at a time.

Double-buffered functions are very useful when your application has a

real-time strip chart displaying the incoming data.

Building Block 4: Cleaning up

The purpose of this building block is to stop the data acquisition and

free any system resources (such as DMA channels) used for the data

acquisition.

DAQ_Clear

is the only function needed for this building block

and is automatically called by the check functions described in the previous

building block when the data acquisition is complete. Therefore, you can

eliminate this last building block if your application continuously calls the

previously described check functions until the data acquisition is complete.

Note DAQ_Clear

does not alter the device configurations made by building block 1.

Double-Buffered Data Acquisition

The double-buffered (

DAQ_DB

) data acquisition functions return data from

an ongoing data acquisition without interrupting the acquisition. These

functions use a double, or circular, buffering scheme that permits half

buffers of data to be retrieved and processed as the data becomes available.

By using a circular buffer, you can collect an unlimited amount of data

without needing an unlimited amount of memory. Double-buffered data

acquisition is useful for applications such as streaming data to disk and

real-time data display.

Initiating double-buffered data acquisition requires some simple changes

to the first and third basic building blocks, Configuration and Checking,

respectively.

In building block 1, turn on double-buffered mode data acquisition through

the

DAQ_DB_Config

call. After the double-buffered mode is enabled, all

subsequent data acquisitions are in double-buffered mode.

In building block 3, different checking functions are needed. Figure 3-10

shows a simple way to monitor the data acquisition in progress and to

retrieve data when they are available.

For further details on double-buffered data acquisition, consult Chapter 4,

NI-DAQ Double Buffering.