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Chapter 4
Analog Input
©
National Instruments Corporation
4-11
Analog Input Timing Signals
In order to provide all of the timing f
u
nctionality described thro
u
gho
u
t this
section, USB-621
x
devices have a flexible timing engine. Fig
u
s
u
mmarizes all of the timing options provided by the analog inp
u
t timing
engine.
Figure 4-4.
Analog Input Timing Options
USB-621
x
devices
u
se AI Sample Clock (ai/SampleClock) and AI Convert
Clock (ai/ConvertClock) to perform interval sampling. As Fig
u
shows, AI Sample Clock controls the sample period, which is determined
by the following eq
u
ation:
1/Sample Period = Sample Rate
20 MHz Time
bas
e
100 kHz Time
bas
e
Progr
a
mm
ab
le
Clock
Divider
Progr
a
mm
ab
le
Clock
Divider
AI
Sa
mple
Clock
Time
bas
e
AI Convert
Clock
Time
bas
e
An
a
log Comp
a
ri
s
on Event
Ctr
n
Intern
a
l O
u
tp
u
t
S
W P
u
l
s
e
Ctr
n
Intern
a
l O
u
tp
u
t
AI Convert Clock
AI
Sa
mple Clock