User's Manual

Chapter 2 Function Reference — DAQ_Op
NI-DAQ FRM for PC Compatibles 2-130
© National Instruments Corporation
invalid gain, NI-DAQ will return an error. NI-DAQ ignores gain for 516 and LPM devices and
the DAQCard-500/700.
buffer is an integer array. buffer has a length equal to or greater than count. When
DAQ_Op
returns with an error number equal to zero, buffer contains the acquired data.
count is the number of samples to be acquired (that is, the number of A/D conversions to be
performed).
Range: 3 through 2
32
– 1 (except for the Lab and 1200 Series and E Series devices).
3 through 65,535 (Lab and 1200 Series devices).
2 through 2
24
(E Series devices).
2 through 2
24
– 3 (PCI-6110E and PCI-6111E) requires an even number of
samples.
2 through 2
24
(PCI-445X).
2 through 2
32
– 1 (PCI-455X).
sampleRate is the sample rate you want in, units of pts/s.
Range: Roughly 0.00153 pts/s through 5,000,000 pts/s. The maximum rate depends on
the type of device.
Note If you are using an SCXI-1200 with remote SCXI, the maximum rate will depend
on the baud rate setting and count. Refer to the SCXI-1200 User Manual for more
details.
Using This Function
DAQ_Op initiates a synchronous process of acquiring A/D conversion samples and storing
them in a buffer.
DAQ_Op does not return control to your application until NI-DAQ acquires
all the samples you want (or until an acquisition error occurs). When you are using posttrigger
mode (with pretrigger mode disabled), the process stores count A/D conversions in the buffer
and ignores any subsequent conversions.
Note If you have selected external start triggering of the DAQ operation, a high-to-low
edge at the STARTTRIG* I/O connector of the MIO-16, 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 the Lab and 1200 Series devices initiates the DAQ operation.
If you are using an E Series device or DSA device, 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 have enabled pretrigger mode, the sample counter does not begin counting acquisitions
until you apply a signal at the stop trigger input. Until you apply this signal, the acquisition
remains in a cyclical mode, continually overwriting old data in the buffer with new data.