Chapter 4
Analog Input
©
National Instruments
4-11
X Series User Manual
If data cannot be transferred across the b
u
s fast eno
u
gh, the FIFO
becomes f
u
ll. New acq
u
isitions overwrite data in the FIFO before
it can be transferred to host memory. The device generates an error
in this case. With contin
u
o
u
s operations, if the
u
ser program does
not read data o
u
t of the PC b
u
ffer fast eno
u
gh to keep
u
p with the
data transfer, the b
u
ffer co
u
ld reach an overflow condition,
ca
u
sing an error to be generated.
•
Hardware-timed single point (HWTSP)
—Typically, HWTSP
operations are
u
sed to read single samples at known time intervals.
While b
u
ffered operations are optimized for high thro
u
ghp
u
t, HWTSP
operations are optimized for low latency and low jitter. In addition,
HWTSP can notify software if it falls behind hardware. These feat
u
res
make HWTSP ideal for real time control applications. HWTSP
operations, in conj
u
nction with the wait for next sample clock
f
u
nction, provide tight synchronization between the software layer and
the hardware layer. Refer to the NI Developer Zone doc
u
ment,
NI-DAQmx Hardware-Timed Single Point Lateness Checking
, for
more information. To access this doc
u
ment, go to
ni.com/info
and
enter the Info Code
daqhwt
s
p
.
Note
(NI USB-634
x
/6351/6353//6361/6363 Devices)
X Series USB devices do not s
u
pport
hardware-timed single point (HWTSP) operations.
Analog Input Triggering
Analog inp
u
t s
u
pports three different triggering actions:
•
Start trigger
•
Reference trigger
•
Pa
u
se trigger
Refer to the
AI Start Trigger Signal
,
AI Reference Trigger Signal
, and
AI Pause Trigger Signal
sections for information abo
u
t these triggers.
An analog or digital trigger can initiate these actions. All MIO X Series
devices s
u
pport digital triggering, b
u
t some do not s
u
pport analog
triggering. To find yo
u
r device triggering options, refer to the specifications
doc
u
ment for yo
u
r device.
Connecting Analog Input Signals
Table 4-3 s
u
mmarizes the recommended inp
u
t config
u
ration for both types
of signal so
u
rces.
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