ADLINK Technology NuDAQ PCI-9222, User Manual

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30 Operation Theory
This method is suitable for applications that need to process A/D
data in real time. In this mode, the timing of the A/D conversion is
fully controlled by the software. The A/D conversion rate is
decided by the software timer and may not be totally precise.
In Software Polling, the channel, gain, and input configuration
(RSE, NRSE, or DIFF) may be specified for each single-point
measurement. For example:
Ch2 with ± 5V input range and single-ended NRSE connection
Continuous Acquisition (Scanning) Mode
Continuous A/D Conversion Clock Source
When the onboard ADC receives a conversion clock signal, it
will trigger an A/D conversion. The conversion clock of PCI-
9222/PCI-9223 may come from three different clock sources:
internal hardware timer, general purpose input channel (GPI 0
~ GPI 7), or SSI (system synchronization interface). Refer to
Figure 4-3.
Figure 4-3: Continuous A/D Conversion Clock Source Block Diagram
You can choose conversion clock source by setting AI source
configuration. But if users want to get the precision acquisition,
the internal hardware timer is recommended.
Continuous Scanning with Internal Hardware Timer
It is recommended that you use this mode if your applications
need a fixed and precise A/D sampling rate. You can
accurately program the period between conversions of
individual channels. There are at least four counters that have
to be specified:
Internal
Timer
SSI
GPI[7..0]
AI Conversion Clock