Programming instructions

© National Instruments Corporation 21-1 DAQ Hardware Overview Guide
21
671 X Devices
This chapter contains overview information on the 671X devices, including
the DAQCard-6715, PCI-6711, PCI-6713, PXI-6711, and PXI-6713. For
more detailed descriptions of the hardware functionality and specifications,
refer to your device user manual.
671 X Device Analog Output
The 671X devices contain four or eight analog output channels numbered 0
through 7. Each analog output channel contains a 12-bit DAC, which
is always configured in bipolar mode. An onboard voltage reference
of +10 V is available for the analog output channels. An external
reference voltage signal can also drive the analog output channels. See
the
AO_Configure function in the NI-DAQ Function Reference Online
Help for more information about configuring the DACs.
Note
The 671X devices require an even number of samples in the waveform buffer due to
FIFO requirements necessary for high-speed data transfers.
671 X Device Waveform Generation
Timing and control on the 671X devices is performed by the National
Instruments Data Acquisition System Timing Controller (DAQ-STC) chip.
The Waveform Generation functions can write values to either one or more
analog output channels continuously using an onboard or external clock to
update the DACs at regular intervals. The values are contained in a buffer
that you allocate and fill. The resultant voltages produced at the analog
output channels depend on the value of the numbers in the buffer and the
level of the reference voltage.
Note
NI-DAQ can use either DMA or interrupt service routines to generate waveforms on
the analog output channels. By default, NI-DAQ uses DMA because DMA is simply more
efficient. Call
Set_DAQ_Device_Info, described in the NI-DAQ Function Reference
Online Help, to force NI-DAQ not to use DMA for waveform generation. DMA is not
supported on DAQCard PCMCIA devices. Interrupts are used by default.