ADLINK PXI-2006 - Manual (Page 52)

42 Operation Theory
Figure 4-13: Scatter/gather DMA for data transfer
In non-chaining mode, the maximum DMA data transfer size is 2M
double words (8M bytes). However, by using chaining mode, scat-
ter/gather, there is no limitation on DMA data transfer size. Users
can also link the de-scriptor nodes circularly to achieve a multi-
buffered mode DMA.
4.2 D/A Conversion
There are 2 channels of 12-bit D/A output available in the DAQ/
PXI-20XX. When using D/A converters, users should assign and
control the D/A converter reference sources for the D/A operation
mode and D/A channels. Users could also select the output polar-
ity: unipolar or bipolar.
The reference selection control lets users fully utilize the multiply-
ing characteristics of the D/A converters. Internal 10V reference
and external reference inputs are available in the DAQ/PXI-20XX.
The range of the D/A output is directly related to the reference.
The digital codes that are up-dated to the D/A converters will mul-
tiply with the reference to generate the analog output. While using
internal 10V reference, the full range would be –10V ~ +9.9951V
in the bipolar output mode, and 0V ~ 9.9976V in the unipolar out-
put mode. While using an external reference, users can reach dif-
ferent output ranges by connecting different references. For
example, if connecting a DC –5V with the external reference, then
the users can get a full range from –4.9976V to +5V in the bipolar
output with inverting char-acteristics due to the negative reference
voltage. Users could also have an amplitude modulated (AM) out-