Chapter 2
NI 5450 Overview
NI PXIe-5450 User Manual
2-74
ni.com
Edge Trigger
A digital signal has two discrete levels: a high level and a low level. When
the signal transitions from high to low or from low to high, a
digital edge
is created. There are two types of edges: rising, which occurs when the
signal transitions from low level to high level, and falling, which occurs
with a transition from high level to low level. Triggers configured to act on
a rising or falling edge of a digital signal are called
edge triggers
.
As the following figure shows, an edge trigger could be configured to occur
either at the place labeled
Falling Edge of Signal
or at
Rising Edge of
Signal
.
Level Trigger
You can configure certain triggers to act when a signal goes below the
defined low level or above the defined high level. Triggers configured to
act in this way are known as
level triggers
. Not all triggers can be
configured to be level triggers.
Software Trigger
A software trigger is generated internally by a programmatic call to the
niFgen Send Software Edge Trigger VI or the
niFgen_SendSoftwareEdgeTrigger
function and can occur at any
time, based upon the conditions specified in the program.
Trigger Sources
Trigger sources are software selectable. You can use any of the following
external input triggers:
•
PFI 0 or PFI 1 on the front panel connectors
•
PXI_TRIG<0..7> lines on the PXI trigger bus backplane
F
a
lling Edge of
S
ign
a
l
Ri
s
ing Edge of
S
ign
a
l
High Level
Low Level
