The Scientist and Engineer's Guide to Digital Signal Processing538
your desk. (There is also a version called the EZ-LAB, using the ADSP-
21062, that plugs into a slot in your computer). There are only four
connections you need to worry about: DC power, a serial connection to your
personal computer, and the input and output signals. A DC power supply and
serial cable are even provided in the kit. The input and output signals are at
audio level, about 1 volt amplitude. Alternatively, a jumper on the board
allows a microphone to be directly attached into the input. The idea is to plug
a microphone into the input, and attach a set of amplified speakers (such as
used with personal computers) to the output. This allows you to hear the effect
of various DSP algorithms.
Analog-to-digital and digital-to-analog conversion is accomplished with an
Analog Devices AD1847 codec (coder-decoder). This is a 16 bit sigma-delta
converter, capable of digitizing two channels (stereo) at a rate of up to 48k
samples/second, and simultaneously outputing two channels at the same rate.
Since the primary use of this board is to process audio signals, the inputs and
outputs are AC coupled with a cutoff of about 20 Hz.
Three push buttons on the board allow the user to generate an interrupt, reset
the processor, and toggle a flag bit that can be read by the system. Four LEDs
mounted on the board can be turned on and off by toggling bits. If you are
ambitious, there are sections of the board that allow you to access the serial
port, link ports (only on the EZ-LAB with its ADSP-21062), and processor bus.
However, these are unpopulated, and you will need to attach the connectors
and other components yourself.
Here's how it works. When the power is applied, the processor boots from an
on-board EPROM (512 kbytes), loading a program that establishes serial
communication with your personal computer. Next, you launch the EZ-Lite
Host program on you PC, allowing you to download programs and upload data
from the DSP. Several prewritten programs come with the EZ-KIT Lite; these
can be run by simply clicking on icons. For instance, a band-pass program
allows you to speak into the microphone, and hear the result after passing
through a band-pass filter. These programs are useful for two reasons: (1) they
allow you to quickly get the system doing something interesting, giving you
confidence that it does work, and (2) they provide a template for creating
programs of your own. Which brings us to our next topic, a design example
using the EZ-KIT Lite.
Design Example: An FIR Audio Filter
After you experiment with the prewritten programs for awhile, you will want
to modify them to gain experience with the programming. Programs can be
written in either assembly or C; the EZ-KIT Lite provides software tools to
support both languages. Later in this chapter we will look at advanced methods
of programming, such as simulation, debugging, and working in an integrated
development environment. For now, we will focus on the easiest way to get
a program to run. Little steps for little feet.