User's Manual

Chapter 2 Function Reference — SCAN_Start
NI-DAQ FRM for PC Compatibles 2-314
© National Instruments Corporation
If you have selected external start triggering of the data acquisition operation, a high-to-low
edge at the STARTTRIG* I/O connector input on the MIO-16/16D, or the EXTTRIG*
connector on the MIO-F-5/16X initiates the data acquisition operation after the
SCAN_Start
call is complete. Otherwise,
SCAN_Start issues a software trigger to initiate the data
acquisition operation before returning.
Note If your application calls DAQ_Start or SCAN_Start, always ensure that you
call
DAQ_Clear before your application terminates and returns control to the
operating system. Unless you make this call (either directly, or indirectly through
DAQ_Check or DAQ_DB_Transfer), unpredictable behavior can result.
You must use the
SCAN_Setup and SCAN_Start functions as a pair. Making a single call to
SCAN_Setup with multiple calls to SCAN_Start will fail and return error noSetupError.
If you have an SC-2040 connected to your DAQ device, NI-DAQ will ignore the
sampTimebase and sampInterval parameters. NI-DAQ automatically supplies these
parameters to optimally match your hardware.
If you select sampTimebase = 0 and scanTimebase = 0, you must use the same source for
both. This requirement is enforced on most MIO devices through hardware because you
connect both timebases to the SOURCE5 I/O connector pin. On E Series devices, if you use
the
Select_Signal function to specify the source of an external sample and external scan
timebase, you must specify the same source for both timebases.