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Chapter 2 Function Reference — DAQ_Start
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National Instruments Corporation 2-139 NI-DAQ FRM for PC Compatibles
Note You need to apply a trigger that you select through the Select_Signal or
DAQ_Config functions to initiate data acquisition. Be aware that if you do not
apply the start trigger,
DAQ_Op does not return control to your application.
Otherwise,
DAQ_Op issues a software trigger to initiate the DAQ operation.
If you select external start triggering for the DAQ operation, a high-to-low edge at the
STARTTRIG* I/O connector input of the MIO16/16D, the EXTTRIG* input of the
AT-MIO-16F-5, AT-MIO-64F-5, and AT-MIO-16X, or a low-to-high edge at the EXTTRIG
input of Lab and 1200 Series devices initiates the DAQ operation after the
DAQ_Start
call is complete. If you are using an E Series or DSA device, you need to apply a trigger that
you select through the
Select_Signal or DAQ_Config functions to initiate data
acquisition. Otherwise,
DAQ_Start issues a software trigger to initiate the DAQ operation
before returning.
If you enable pretrigger mode, the sample counter does not begin counting acquisitions until
a signal is applied at the stop trigger input. Until this signal is applied, the acquisition remains
in a cyclical mode, continually overwriting old data in the buffer with new data.
Note If your application calls DAQ_Start, SCAN_Start, or Lab_ISCAN_Start,
always make sure that you call
DAQ_Clear before your application terminates and
returns control to the operating system. Unpredictable behavior can result unless
you make this call (either directly, or indirectly through
DAQ_Check or
DAQ_DB_Transfer
)
.