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Chapter 2 Function Reference — AO_Change_Parameter
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National Instruments Corporation 2-37 NI-DAQ FRM for PC Compatibles
Memory Transfer Width
When doing waveform generation on PCI E Series boards that use the PCI-MITE for DMA
transfers, NI-DAQ transfers data from host memory to the DAQ device 16 bits at a time. This
allows for the finest level of control and is necessary to properly support features like old data
stop and partial transfer stop (see the NI-DAQ function
WFM_DB_Config).
It is also possible to transfer data from host memory to the DAQ device 32 bits at a time, which
requires fewer PCI bus cycles so that the DAQ device functions more effectively with the PCI
bus. The only drawback is that when using old data stop and partial transfer stop, the
waveform may stop one sample earlier than you would otherwise expect.
To set the memory transfer width, set paramID to
ND_MEMORY_TRANSFER_WIDTH and set
paramValue to either 16 or 32. You may specify any channel in the waveform group, and the
setting will apply to all channels in the group.
Note
This option is valid only for PCI/CPCI/PXI E Series devices. For 61XX devices,
only even-sized buffers are allowed, and the memory transfer width is always
32 bits.