User`s guide

24 • Operation Theory
4
Operation Theory
The operation theory of the functions on the DAQ/PXI-22XX is described in
this chapter. The functions include the A/D conversion, D/A conversion,
Digital I/O and General Purpose Counter / Timer. The operation theory can
help you understand how to configure and program the DAQ/PXI-22XX.
4.1 A/D Conversion
When using an A/D converter, users should firs t 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 polarities (Unipolar/Bipolar).
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 e nd of an A/D conversion, the A/D data is buffered in a Data FIFO.
The A/D data can now be transferred into the PC's memory for further
processing.
Two acquisition modes, Software Polling and Scan acquisition are de-
scribed below. Timing, trigger modes, trigger sources, and transfer meth-
ods are included.