Push-Button-Controlled Demultiplexer - Analog Devices AN-951 Application Note

Application Note

PUSH-BUTTON-CONTROLLED DEMULTIPLEXER

This example uses a set of two push-buttons to control a
demultiplexer, which allows a 1 kHz sine wave to be output
on any of eight possible outputs.
The table entries in this case are slightly different because of the
number formats used in the DSP. There are two main formats
used by SigmaDSP: integer format (28.0) and decimal format
(5.23). All audio data and most parameters are represented in
5.23 decimal format within the DSP. Most GPIO-related signals
are represented in 28.0 integer format because it increases the
range of allowable values they can take.
In SigmaStudio index tables, the index value is represented
in 28.0 integer format, whereas the output is in 5.23 decimal
format. However, because this 5.23 output signal is used to
control the demultiplexer (which accepts a 28.0 input format),
number formatting is required within the index table.
To convert between 28.0 integer format and 5.23 decimal
format, use Equation 3 and Equation 4. Equation 3 converts
28.0 to 5.23 while Equation 4 converts 5.23 to 28.0.
−
23
= n ×
n 2
. 5 23 28 0 .
(3)
Figure 25. Push-Button-Controlled Demultiplexer Signal Flow
Rev. A | Page 11 of 20
= n × 23
n 2
28 0 . . 5 23
The first eight indices, converted to 5.23 number format, are
shown in Figure 24.
Figure 24. Push-Button-Controlled Demultiplexer Index Table
The cell names as they appear in the software and the number
of each used in this example are as follows: GPIO Input (2),
Interface Read (1), Up/Down Control with Lookup Table (1),
Interface Write (1), Tone (lookup/sine) (1), Index Selectable
Demultiplexer (1), and Output (8).
AN-951
(4)