National Instruments Data Acquisition Device NI USB-621x - Analog Input Timing Signals

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 functionality described throughout this
section, USB-621x devices have a flexible timing engine. Figure 4-4
summarizes all of the timing options provided by the analog input timing
engine.
Figure 4-4. Analog Input Timing Options
USB-621x devices use AI Sample Clock (ai/SampleClock) and AI Convert
Clock (ai/ConvertClock) to perform interval sampling. As Figure 4-5
shows, AI Sample Clock controls the sample period, which is determined
by the following equation:
1/Sample Period = Sample Rate
20 MHz Timebase
100 kHz Timebase
Programmable
Clock
Divider
Programmable
Clock
Divider
AI Sample
Clock
Timebase
AI Convert
Clock
Timebase
Analog Comparison Event
Ctr n Internal Output
SW Pulse
Ctr n Internal Output
AI Convert Cloc
k
AI Sample Clock