Operation Theory
19
Software Polling
This is the easiest way to acquire a single A/D data. The A/D con-
verter performs one conversion whenever the dedicated software
command is executed. The software would poll the conversion
status and read the A/D data back when it is available.
This method is suitable for applications that need to acquire A/D
data in real time. In this mode, the timing of the A/D conversion is
fully controlled by software. However, it would be difficult to main-
tain a fixed A/D sampling rate.
Programmable Scan
This method is suitable for applications that need to acquire A/D
data at a precise and fixed rate. A scan is a group of multiple
channel samples and the scan interval is defined by the
SI_counter. Likewise, the sample in-terval of the multiple channels
is defined by the SI2_counter. Please refer to Table 4-4 for more
information.
DAQ/PXI-2500 series can sample multiple channels in continu-
ous/discontinuous ascending sequence. For example, users may
program DAQ/PXI-2500 series to perform a scan in the channel
sequence of 1-2-4-1-2-4…
There are 3 Trigger Modes available in Programmable Scan. They
are Post-Trigger, Delay-Trigger, Post/Delay-Trigger with Retrigger.
Midscale - LSB 4.999389V 2.499694V 1.249847V 1.249923V
3FFF
-FSR
0V
0V
0V
0V
2000
Magnitude
Unipolar Input Range
Digital code
Table 4-2: Unipolar Input Range and Converted Digital Codes