ADLINK PXI-2006 - Manual (Page 37)

Operation Theory 27
4 Operation Theory
The operation theory of the functions on the DAQ/PXI-20XX is
described in this chapter. The functions include the A/D conver-
sion, D/A conversion, Digital I/O and General Purpose Counter/
Timer. The operation theory can help you understand how to con-
figure and program the DAQ/PXI-20XX.
The whole DAQ/PXI-2000 series cards, including DAQ/PXI-20XX,
DAQ/PXI-22XX and DAQ/PXI-25XX, are designed based on the
same logic-timing template of DAQ/PXI-22XX. In the DAQ/PXI-
22XX cards, all the A/D related timings are for multiplexing A/D
sampling based on scan-ning, so that DAQ/PXI-20XX also adopts
the same concept, except there is only one conversion signal in a
scan which could generate up to 4 samples from the different 4
channels at the same time. In the following description, to conform
to the original timing design, we still use “scan” as the unit of A/D
data acquisition. All the DA and GPTC functions are the same in
DAQ/PXI-20XX and DAQ/PXI-22XX, while DAQ/PXI-25XX pro-
vides im-proved DA timing comparing the former 2 series.
4.1 A/D Conversion
When using an A/D converter, users should first know about the
properties of the signal to be measured. Users can decide which
channel to use and where to connect the signals to the card.
Please refer to 3.2 for signal connections. In addition, users
should define and control the A/D signal configurations, including
channels, gains, and A/D signal types.
There are 2 ways to initiate A/D conversion, either by Software
Polling or Programmable Scan Acquisition; these are described
below.
The A/D acquisition is initiated by a trigger source; users must
decide how to trigger the A/D conversion. The data acquisition will
start once a trigger condition is matched.
After the end of A/D conversion, the A/D data is buffered in a Data
FIFO. The A/D data should be transferred into the PC's memory
for further processing.