User manual

Chapter 3 Software Overview
© National Instruments Corporation 3-113 NI-DAQ User Manual for PC Compatibles
applications. The distinction between the two categories is simple—
single-channel applications do not involve automatic channel switching
by the hardware during an analog input process; channel-scanning
applications do.
After you have set up the SCXI system, single-channel applications use
the
AI
or the
DAQ
class of functions described earlier in this chapter to
acquire the input data. To acquire data from more than one channel, you
need multiple
AI
or
DAQ
function calls, and you might need explicit SCXI
function calls to change the selected SCXI channel; this specific type of
single-channel application is called software scanning.
After you have set up the SCXI system, channel-scanning applications use
the
SCAN
and
Lab_ISCAN
classes of functions described earlier in this
chapter to acquire the input data.
Building Analog Input Applications in
Multiplexed Mode
Multiplexed applications require the use of SCXI functions to select
the multiplexed channels, select the programmable module features,
route signals on the SCXIbus, and program Slot 0. After you have set
up the SCXI chassis and modules, you can use the
AI
,
DAQ
,
SCAN
,and
Lab_ISCAN
functions to acquire the data either with a plug-in DAQ device
or the SCXI-1200. The channel parameter that is passed to each of these
functions is almost always 0 because the multiplexed output of a module
is connected by default to analog input channel 0 of the DAQ device or
SCXI-1200. If you are using a PXI DAQ device with an internal connection
to the PXI-1010 or PXI-1011 SCXIbus, then
ND_PXI_SC
is the channel
parameter. When you use multiple chassis, the modules in each chassis are
multiplexed to a separate analog input channel. In that case, the channel
parameters of the
AI
,
DAQ
,
SCAN
,and
Lab_ISCAN
functions should be the
DAQ device channel that corresponds to the chassis you want for the
operation. You cannot use the SCXI-1200 with multiple chassis.