Chapter 7
Counters
©
National Instruments
7-45
X Series User Manual
Counter
n
HW Arm Signal
The Co
u
nter
n
HW Arm signal enables a co
u
nter to begin an inp
u
t or o
u
tp
u
t
f
u
nction.
To begin any co
u
nter inp
u
t or o
u
tp
u
t f
u
nction, yo
u
m
u
st first enable, or arm,
the co
u
nter. In some applications, s
u
ch as a b
u
ffered edge co
u
nt, the
co
u
nter begins co
u
nting when it is armed. In other applications, s
u
ch as
single p
u
lse-width meas
u
rement, the co
u
nter begins waiting for the Gate
signal when it is armed. Co
u
nter o
u
tp
u
t operations can
u
se the arm signal
in addition to a start trigger.
Software can arm a co
u
nter or config
u
re co
u
nters to be armed on a
hardware signal. Software calls this hardware signal the Arm Start Trigger.
Internally, software ro
u
tes the Arm Start Trigger to the Co
u
nter
n
HW Arm
inp
u
t of the co
u
nter.
Routing Signals to Counter
n
HW Arm Input
Any of the following signals can be ro
u
ted to the Co
u
nter
n
HW Arm inp
u
t:
•
RTSI <0..7>
•
PFI <0..15>
•
AI Reference Trigger (ai/ReferenceTrigger)
•
AI Start Trigger (ai/StartTrigger)
•
PXI_STAR
•
PXIe-DSTAR<A,B>
•
Analog Comparison Event
•
Change Detection Event
A co
u
nter’s Internal O
u
tp
u
t can be ro
u
ted to a different co
u
nter’s HW Arm.
Some of these options may not be available in some driver software.
Counter
n
Sample Clock Signal
Use the Co
u
nter
n
Sample Clock (Ctr
n
SampleClock) signal to perform
sample clocked acq
u
isitions and generations.
Yo
u
can specify an internal or external so
u
rce for Co
u
nter
n
Sample Clock.
Yo
u
also can specify whether the meas
u
rement sample begins on the rising
edge or falling edge of Co
u
nter
n
Sample Clock.
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