©
National Instruments Corporation
12-1
12
Triggering
A trigger is a signal that ca
u
ses an action, s
u
ch as starting or stopping the
acq
u
isition of data. When yo
u
config
u
re a trigger, yo
u
m
u
st decide how
yo
u
want to prod
u
ce the trigger and the action yo
u
want the trigger to ca
u
se.
All USB-621
x
devices s
u
pport internal software triggering, as well as
external digital triggering. For information abo
u
t the different actions
triggers can perform for each s
u
b-system of the device, refer to the
following sections:
•
The
Analog Input Digital Triggering
•
The
Analog Output Digital Triggering
•
The
Triggering with a Digital Source
Yo
u
r USB-621
x
device can generate a trigger on a digital signal. Yo
u
m
u
st
specify a so
u
rce and an edge. The digital so
u
rce can be any inp
u
t PFI
signal.
The edge can be either the rising edge or falling edge of the digital signal.
A rising edge is a transition from a low logic level to a high logic level.
A falling edge is a high to low transition. Fig
u
re 12-1 shows a falling-edge
trigger.
Figure 12-1.
Falling-Edge Trigger
5 V
0 V
F
a
lling Edge Initi
a
te
s
Acq
u
i
s
ition
Digit
a
l Trigger
