ADLINK PXI-2502 - Manual (Page 27)

Operation Theorem
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4.1.2 Software Polling
This is the easiest way to acquire a single A/D data. The A/D converter
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 maintain a fixed A/D sampling
rate.
4.1.3 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 4.1.4 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. Please
refer to Table 4.1.3 for a brief summary on Trigger Modes and their Trigger
Sources.
Trigger Mode Description Trigger Sources
Post-Trigger
Perform a scan right after the
trigger occurs.
Delay-Trigger
Scan delayed by the amount
of time programmed after the
trigger
Post/Delay-Trigger
with Retrigger
Perform repeated scan while
trigger occurs and it could be
under Post-Trigger or De-
lay-Trigger mode.
Software Trigger
Digital Trigger
Analog Trigger
SSI AD Trigger
Table 4.1.3 Trigger Modes and Corresponding Trigger Sources