Chapter 7
Counters
X Series User Manual
7-2
ni.com
generations. The embedded co
u
nters cannot be programmed independent
of the main co
u
nter; signals from the embedded co
u
nters are not ro
u
table.
Counter Timing Engine
Unlike analog inp
u
t, analog o
u
tp
u
t, digital inp
u
t, and digital o
u
tp
u
t,
X Series co
u
nters do not have the ability to divide down a timebase to
prod
u
ce an internal co
u
nter sample clock. For sample clocked operations,
an external signal m
u
st be provided to s
u
pply a clock so
u
rce. The so
u
rce
can be any of the following signals:
•
AI Sample Clock
•
AI Start Trigger
•
AI Reference Trigger
•
AO Sample Clock
•
DI Sample Clock
•
DI Start Trigger
•
DO Sample Clock
•
CTR
n
Internal O
u
tp
u
t
•
Freq O
u
t
•
PFI <0..15>
•
PXI_Trig <0..7>
•
PXIe-DSTAR<A,B>
•
Change Detection Event
•
Analog Comparison Event
Not all timed co
u
nter operations req
u
ire a sample clock. For example, a
simple b
u
ffered p
u
lse width meas
u
rement latches in data on each edge of a
p
u
lse. For this meas
u
rement, the meas
u
red signal determines when data is
latched in. These operations are referred to as implicit timed operations.
However, many of the same meas
u
rements can be clocked at an interval
with a sample clock. These are referred to as sample clocked operations.
Table 7-1 shows the different options for the different meas
u
rements.
Note
All hardware-timed single point (HWTSP) operations are sample clocked.
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