Programming instructions

Chapter 21 Common SCXI Applications
LabVIEW Data Acquisition Basics Manual 21-20
© National Instruments Corporation
Use the
iteration
input to optimize your digital operation. When
iteration
is
0
(default), LabVIEW calls the DIO Port Config VI (an Advanced VI)
to configure the port. If
iteration
is greater than zero, LabVIEW bypasses
reconfiguration and remembers the last configuration, which improves
performance. You can wire this input to an iteration terminal of a loop.
Every time you call the DIO Port Config VI the digital line values are reset
to default values. If you want to maintain the integrity of the digital values
from one loop iteration to another, do not set iteration to
0
except for the
first iteration of the loop.
For an example on SCXI digital output, refer to SCXI-116x Digital
Output VI located in
labview\examples\daq\scxi\scxi_dig.llb
.
Even though this VI uses Advanced VIs, it is functionally equivalent to
the Easy Digital VI, Write to Digital Port.
Note
If you also are using SCXI analog input modules, make sure your cabling
DAQ device is cabled to one of them.
Multi-Chassis Applications
Multiple SCXI-1000, SCXI-1000DC, or SCXI-1001 chasses can be
daisy-chained using the SCXI-1350 or SCXI-1346 multichassis cable
adapters and an MIO Series DAQ device other than the
DAQPad-MIO-16XE-50. Every module in each of the chassis must be in
multiplexed mode. Only one of the chassis will be connected directly to the
DAQ device. Also, if you are using Remote SCXI with RS-485, you can
daisy chain up to 31 chasses on a single RS-485 port. Because you can only
configure up to 16 devices on the NI-DAQ Configuration utility, you can
only have up to 16 SCXI-1200s in your system.
Note
Lab Series devices, LPM devices, DAQCard-500, 516 devices, DAQCard-700,
1200 Series (other than SCXI-1200), and DIO-24 devices do not support
multi-chassis applications.
If you use the DAQ Channel Wizard to configure your analog input
channels, you simply address channels in multiple chasses by their channel
names. Channel names can be combined, separated by commas, to measure
data from multiple modules in a daisy-chain configuration at the same time.
For example, if you have a named channel called
temperature
on one
module in the daisy-chain and
pressure
on another module in the same
daisy-chain, your
channels
array could be
temperature
,
pressure
. You
must enter the chasses in a sequential order in the NI-DAQ Configuration
Utility, assigning the first chassis in the chain an ID number of 1, the second
chassis an ID number of 2, and so forth.