ADLINK PXI-2006 - Manual (Page 41)

Operation Theory 31
This method is very suitable for applications that needs to process
A/D data in real time. Under this mode, the timing of the A/D con-
version is fully controlled under software. However, it is difficult to
control the A/D con-version rate.
Specifying Channel, Gain, and Polarity
In both the Software Polling and programmable scan acquisi-
tion mode, the channel, gain, and polarity for each channel can
be specified and selected. With this configuration, signal
sources must be connected to the right connector as the speci-
fied settings.
When the specified channels have been sampled from the first
to the last data, the settings applied to each channel would be
the same until next change.
Example:
Typically you can set the input configuration for different chan-
nels:
Ch1 with unipolar ±10V
Ch2 with bipolar ±2.5V
Ch3 with no signal input (disabled)
Ch4 with bipolar ±1.25V
Programmable scan acquisition mode
Scan Timing and Procedure
It's recommended that this mode be used if your applications
need a fixed and precise A/D sampling rate. You can accu-
rately program the period between conversions of individual
channels. There are at least 2 counters, which need to be
specified:
SI_counter (24 bit):Specify the Scan Interval =
SI_counter / TIMEBASE
PSC_counter (24 bit):Specify Post Scan Counts,
i.e. the total sample count after a trigger
event,
The acquisition timing and the meanings of the 2 counters are
illustrated in Figure 10. The SCAN_START signal is derived from
the SI_counter, which will lead to the A/D conversion signal gener-
ation. Note that the DAQ/PXI-20XX series is a simultaneous sam-