National Instruments DAQ X Series User Manual page 79

Chapter 4 Analog Input
Other Timing Requirements
The sample and conversion level timing of MIO X Series devices work
such that some clock signals are gated off unless the proper timing
requirements are met. For example, the device ignores both AI Sample
Clock and AI Convert Clock until it receives a valid AI Start Trigger signal.
Similarly, the device ignores all AI Convert Clock pulses until it recognizes
an AI Sample Clock pulse. Once the device receives the correct number of
AI Convert Clock pulses, it ignores subsequent AI Convert Clock pulses
until it receives another AI Sample Clock. However, after the device
recognizes an AI Sample Clock pulse, it causes an error if it receives an
AI Sample Clock pulse before the correct number of AI Convert Clock
pulses are received.
Figures 4-18, 4-19, 4-20, and 4-21 show timing sequences for a
four-channel acquisition (using AI channels 0, 1, 2, and 3) and demonstrate
proper and improper sequencing of AI Sample Clock and AI Convert
Clock.
AI Sample Clock
AI Convert Clock
Channel Measured 0 1 2 3
Convert Period
Figure 4-18. Scan Overrun Condition; AI Sample Clock Too Fast For Convert Clock
Causes an Error
AI Sample Clock
AI Convert Clock
0 1 2 3 0 1 2 3 0 1 2 3
Channel Measured
Sample #1 Sample #2 Sample #3
Figure 4-19. AI Convert Clock Too Fast For AI Sample Clock;
AI Convert Clock Pulses Are Ignored
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