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Chapter 2 Function Reference — WFM_DB_Transfer
NI-DAQ FRM for PC Compatibles 2-416
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National Instruments Corporation
buffer is the array of new data that is to be transferred into the waveform buffer(s).
WFM_DB_Transfer can transfer new data to more than one waveform buffer, except on PCI
E Series devices. For example, if two channels use separate waveform buffers (you called
WFM_Load once for each channel), you can use a single call to WFM_DB_Transfer to transfer
data to both waveform buffers. If numChans is greater than 1, the data in the buffer must be
interleaved and data for each channel must follow the order given in chanVect.
count holds the number of new data points contained in buffer. When you make repeated
calls to
WFM_DB_Transfer during a waveform generation, it is most efficient if the amount
of data transferred for each channel is equal to one-half the number of data points for the
channel in the channel’s waveform buffer. For example, suppose channel 0 is using a
waveform buffer of size 100 and channel 1 are each is using a waveform buffer of size 100.
WFM_DB_Transfer should transfer 50 to channel 0 and 50 to channel 1, giving count a value
of 100. If NI-DAQ makes transfers to more than one waveform buffer, it is most efficient if
all the waveform buffers contain the same number of samples for each channel.
(AT-AO-6/10 only) For group 1 channels using DMA, if you enable oldDataStop, transfers
of less than half the number of samples in the circular waveform buffer are only allowed if
you enable partialTransferStop.
Using This Function
Use WFM_DB_Transfer to transfer new data into one or more waveform buffers as
waveform generation is in progress. The double-buffered mode, with oldDataStop set to 1,
ensures that NI-DAQ generates each data point for a specified output channel exactly once.
If partialTransferStop is enabled, a transfer of less than half of the waveform buffer size of
a channel stops the waveform generation when NI-DAQ has output the partial half buffer.
(AT-MIO-16F-5 only) If the waveform buffer that you used in calling
WFM_Load was aligned
by calling
Align_DMA_Buffer, WFM_DB_Transfer automatically indexes to the correct
starting index in the waveform buffer, if necessary. You need not align the buffer used in the
WFM_DB_Transfer call.