Cirrus Logic CDB5451A - Manual (Page 15)

CDB5451A
DS458DB3 15
3.2.3 The Conversion Window
Refer to Figure 5. After the user presses on the
green-colored “START” button in this window, the
software will begin to collect data for all six chan-
nels of the CS5451A. For each of the six channels,
a certain number of continuous instantaneous data
samples are bundled together. The period over
which each bundle of samples is taken is called a
“computation cycle.” The user controls the number
of instantaneous data samples that will be taken
(per channel) during one computation cycle by ad-
justing the number in the box labeled “Evaluation
Software Cycle Count.” Note that the default value
for this is set to 4000. Thus during every computa-
tion cycle, the PC software will acquire 4000 sam-
ples (from each of the six channels) and it will
update the on-screen results of all six channels af-
ter calculating the results on each successive set
of 4000 samples. The results that are displayed on
this screen are therefore updated after each com-
putation cycle. Note that the results of the very first
computation cycle (after the “START” button has
been activated) will not be valid. Accuracy of the
Mean/Std. Dev/RMS results increases as the
“Evaluation Software Cycle Count:” value is in-
creased.
The user should understand how to interpret the
values that are displayed in the 4x6 array of num-
ber boxes in the Conversion Window. The result
values displayed in these 24 numeric output boxes
are expressed on a normalized scale. The highest
value (0.999...) represents the highest digital out-
put code that can be issued from the CS5451A
(which is +32767), while the lowest value -0.999...
represents the lowest output code that can be is-
sued from the CS5451A (which is -32768). This is
because the CS5451A issues instantaneous out-
put codes as two’s complement 16-bit words.
Therefore, the range of values that can be returned
from the CS5451A are between -32768 and
+32767. The CS5451A issues instantaneous da-
ta, and every computation cycle, the software com-
putes/displays the quantities which are described
below:
Figure 5. Conversion Window