ADLINK PXI-2208 - Manual (Page 45)

Operation Theory 33
4 Operation Theory
The operation theory of the DAQ-/DAQe-/PXI-2204/2205/2206/
2208 card functions are described in this chapter. The functions
include the A/D conversion, D/A conversion, digital I/O, and gen-
eral purpose counter/timer. The operation theory can help you
understand how to configure and program the DAQ-/DAQe-/PXI-
2204/2205/2206/2208 card.
4.1 A/D Conversion
When using an A/D converter, you must know about the properties
of the signal to be measured. You may decide which channel to
use and how to connect the signals to the card. 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 and you must
decide how to trigger the A/D conversion. The data acquisition will
start once a trigger condition is matched.
After the end 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 system
memory for further processing.
DAQ-/DAQe-/PXI-2204/2208 AI Data Format
Synchronous Digital Inputs (DAQ-/DAQe-/PXI-2204 only)
When each A/D conversion is completed, the 14-bits converted
digital data accompanied with 2 bits of SDI<1..0>_X per chan-
nel from J5 will be latched into the 16-bit register and data
FIFO as shown in Figure 4-1 and Figure 4-2. Therefore, you
can simultaneously sample one analog signal with four digital
signals. The data format of every acquired 16-bit data is as fol-
lows:
D11, D10, D9 ....... D1, D0, b3, b2, b1, b0
Where
D11, D10, D9 ....... D1, D0: 2’s complement A/D
12-bit data
b3, b2, b1, b0: Synchronous Digital Inputs
SDI<3..0>