National Instruments Data Acquisition Device NI USB-621x, User Manual

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Chapter 4 Analog Input
© National Instruments Corporation 4-11 NI USB-621x User Manual
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 re 4-4
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 re 4-5
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