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Chapter 4
Analog Input
X Series User Manual
4-58
ni.com
Note
Waveform information from LabVIEW will not reflect the delay between triggers.
They will be treated as a contin
u
o
u
s acq
u
isition with constant t0 and dt information.
Note
(NI USB-6356/6366 Devices)
Some X Series devices internally transfer data in sample
pairs, as opposed to single samples. This implementation allows for greater data
thro
u
ghp
u
t. However, if an acq
u
isition on these devices acq
u
ires an odd n
u
mber of total
samples, the last sample acq
u
ired cannot be transferred.
To ens
u
re this condition never occ
u
rs, NI-DAQmx adds a backgro
u
nd channel for finite
acq
u
isitions that have both an odd n
u
mber of channels and an odd n
u
mber of
samples-per-channel. The backgro
u
nd channel is also added when performing any
reference-triggered finite acq
u
isition. Data from the backgro
u
nd channel is only visible
when reading in RAW mode.
For maxim
u
m efficiency in b
u
s bandwidth and onboard FIFO
u
se,
u
se an even n
u
mber of
samples-per-channel or an even n
u
mber of channels for finite acq
u
isitions, so the
backgro
u
nd channel is not added.
Reference triggers are not retriggerable.
Using a Digital Source
To
u
se AI Start Trigger with a digital so
u
rce, specify a so
u
rce and an edge.
The so
u
rce can be any of the following signals:
•
PFI <0..15>
•
RTSI <0..7>
•
Co
u
nter
n
Internal O
u
tp
u
t
•
PXI_STAR
•
PXIe-DSTAR<A,B>
The so
u
rce also can be one of several other internal signals on yo
u
r DAQ
device. Refer to
Device Routing in MAX
in the
NI-DAQmx Help
or the
LabVIEW Help
for more information.
Yo
u
also can specify whether the meas
u
rement acq
u
isition begins on the
rising edge or falling edge of AI Start Trigger.
Using an Analog Source
When yo
u
u
se an analog trigger so
u
rce, the acq
u
isition begins on the
first rising edge of the Analog Comparison Event signal.
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