Chapter 6
Digital I/O
X Series User Manual
6-4
ni.com
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
/635
x
/636
x
Devices)
X Series USB devices do not s
u
pport
hardware-timed single point (HWTSP) operations.
Digital Input Triggering
Digital inp
u
t s
u
pports three different triggering actions:
•
Start trigger
•
Reference trigger
•
Pa
u
se trigger
Refer to the
DI Start Trigger Signal
,
DI Reference Trigger Signal
, and
DI Pause Trigger Signal
sections for information abo
u
t these triggers.
An analog or digital trigger can initiate these actions. All 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.
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