Chapter 7
Counters
X Series User Manual
7-52
ni.com
Synchronization Modes
The 32-bit co
u
nter co
u
nts
u
p or down synchrono
u
sly with the So
u
rce
signal. The Gate signal and other co
u
nter inp
u
ts are asynchrono
u
s to the
So
u
rce signal, so X Series devices synchronize these signals before
presenting them to the internal co
u
nter.
Depending on how yo
u
config
u
re yo
u
r device, X Series devices
u
se one of
three synchronization methods:
•
100 MHz Source Mode
•
External Source Greater than 25 MHz
•
External or Internal Source Less than 25 MHz
100 MHz Source Mode
In 100 MHz so
u
rce mode, the device synchronizes signals on the rising
edge of the so
u
rce, and co
u
nts on the third rising edge of the so
u
rce. Edges
are pipelined so no co
u
nts are lost, as shown in Fig
u
re 7-40.
Figure 7-40.
100 MHz Source Mode
External Source Greater than 25 MHz
With an external so
u
rce greater than 25 MHz, the device synchronizes
signals on the rising edge of the so
u
rce, and co
u
nts on the third rising edge
of the so
u
rce. Edges are pipelined so no co
u
nts are lost, as shown in
Fig
u
re 7-41.
Figure 7-41.
External Source Greater than 25 MHz
100 MHz
S
o
u
rce
S
ynchronize
Co
u
nt
Extern
a
l
S
o
u
rce >25 MHz
S
ynchronize
Co
u
nt
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