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Chapter 5
Analog Output
5-6
ni.com
•
(USB-6218 Devices)
PFI <0..3>, PFI <8..11>
•
AI Start Trigger (ai/StartTrigger)
The so
u
rce also can be one of several internal signals on yo
u
r USB-621
x
device. Refer to
Device Routing in MAX
in the
NI-DAQmx Help
or the
LabVIEW Help
in version 8.0 or later for more information.
Yo
u
also can specify whether the waveform generation begins on the rising
edge or falling edge of AO Start Trigger.
Routing AO Start Trigger to an Output Terminal
Yo
u
can ro
u
te AO Start Trigger o
u
t to any o
u
tp
u
t PFI terminal. The o
u
tp
u
t
is an active high p
u
lse.
AO Pause Trigger Signal
Use the AO Pa
u
se Trigger signal (ao/Pa
u
seTrigger) to pa
u
se the generation
of AO samples in a DAQ seq
u
ence. That is, when AO Pa
u
se Trigger is
active, no samples occ
u
r.
If the AO Sample Clock is derived from AO Sample Clock Timebase—for
example, when yo
u
choose the onboard 20 MHz or 100 kHz
Timebase—the AO Sample Clock Timebase is divided down by a
programmable clock divider circ
u
it and then drives AO Sample Clock,
as shown in Fig
u
re 5-3.
In this case, AO Pa
u
se Trigger masks off AO Sample Clock Timebase
p
u
lses from the programmable clock divider.
For example, an internal timebase is ro
u
ted to AO Sample Clock Timebase
and the Timebase divisor is 5, as shown in Fig
u
re 5-4. AO Sample Clock
normally asserts once for every five periods of AO Sample Clock
Timebase; the programmable clock divider co
u
nts down from 4 to 0. When
AO Pa
u
se Trigger is asserted, the programmable clock divider ignores
p
u
lses of AO Sample Clock Timebase.