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Chapter 2 Function Reference — DAQ_DB_Transfer
NI-DAQ FRM for PC Compatibles 2-124
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National Instruments Corporation
DAQ_DB_Transfer
Format
status = DAQ_DB_Transfer (deviceNumber, halfBuffer, ptsTfr, daqStopped)
Purpose
Transfers half of the data from the buffer being used for double-buffered data acquisition to
another buffer, which is passed to the function, and waits until the data to be transferred is
available before returning. You can execute
DAQ_DB_Transfer repeatedly to return
sequential half buffers of the data.
Parameters
Input
Output
Parameter Discussion
halfBuffer is an integer array. The size of the array must be at least half the size of the circular
buffer being used for double-buffered data acquisition.
ptsTfr is the number of points transferred to halfBuffer. This value is always equal to half
the number of samples specified in
DAQ_Start, SCAN_Start, or Lab_ISCAN_Start unless
the acquisition has not yet begun, or the acquisition stopped while in pretrigger mode. In the
former case, until NI-DAQ applies an external start trigger, ptsTfr is 0. In the latter case
(pretrigger mode), the acquisition can stop at any point in the circular buffer after acquiring
the specified number of samples after the board receives NI-DAQ applies a pulse at
STOPTRIG for the MIO-16 stop trigger input. Refer to EXTTRIG* of the non-E Series MIO
devices, or to EXTTRIG of Lab and 1200 Series devices. If you are using all E Series devices,
see the
Select_Signal function for information about the external timing signals. Thus,
Name Type Description
deviceNumber i16 assigned by configuration utility
Name Type Description
halfBuffer [i16] integer array to which the data is to be transferred
ptsTfr u32 number of points transferred
daqStopped i16 indicates the completion of a pretrigger mode
acquisition