Low Cost DSP Based System for Signal Processing and Control
Yu Wang

Yanfang Wang

Department of Modern Physics, University of Science and Technology of China
P.O. Box No.4, Hefei, Anhui,230027, China
Abstract
For control and data acquisition systems, DSP(DigitalSignal Processor) plays an important role in signalprocessing, data correction and bus control. This article
describes a system built at the FELab (Fast Electronics
Laboratory) which use DSPs as a core processor and PC asa host. It is a digital platform which can be used in highspeed real time data processing and control. The authors
also introduce some potential applications of the platform,
especially an effective real-time image enhancing
application.
The platform costs less than US$500 (PC is notincluded), for most research and even educational projects,
this is affordable.

architecture, a processor architecture with separated
program memory and data memory. This architecture
enables it to get instructions and data at the same time.
Besides, it has relatively big(80k bytes) on-chip memory.
The core processing unit of the chip can neatly access theon-chip memory faster than with external memory. As aresult, ADSP2181 can realize many algorithms such ascorrelation, convolution, accumulation, filtering etc.
effectively.
Analog Device Inc. also provides an inexpensive kit forthe convenience of users. The kit includes an ADSP2181,aset of CODEC chips, an RS-232 serial port interface, and amonitor program executed under Windows3.X. Users
could take advantage of this kit to be familiar with theDSP.

1 Introduction

2.2 Schematic design

Data acquisition and signal processing is now being
broadly used in many fields. With the progress in the newtechniques, people study fast, wide-band signals more andmore. Under some conditions, signals are even required to
be processed in real time, such as real time parameters
extracting and feedback control. Thus it is necessary todevelop a system to handle this task. Moreover, we need
not only a system that can do it, but also a system we canafford.
A general purpose, low cost, easy to use, real time
digital platform based on a DSP was made at ourlaboratory. It is assembled with three major parts: analog
to digital converter(ADC), data processing chip, digital toanalog converter(DAC). An ADSP2181 functions as a core
processor to manage the whole system. The ADC andDAC are the interfaces to the real world. So this platform
can acquire signals from the analog domain, process themin digital domain with a number of flexible, powerful DSP
algorithms, then return the results to the analog domain.
Accordingly, it is well suited for resolving some dataacquisition, test and measurement, and feedback control
problems.

Because most of the instructions of ADSP2181 areexecuted in single clock period, the code executing time iseasy to be predicted. We directly use the program timing toproduce ADC sampling clock. By this technique, thehandshaking between DSP and ADC can be done easily.
Furthermore, the system sampling rate is flexible and theplatform can give full play to its processing potential.
For general applications, the on-chip memory is bigenough. But for some mass data applications, such as long
period wide-band signals analysis, the on-chip memory is
too small to attain the requirements. We add 512k x 16 bit
off-chip memory to adapt this kind of applications.

2 System design
2.1 A brief introduction to the ADSP2181
ADSP2181 is a 33MHz, 16bit fixed point DSP chipfrom Analog Device Inc.. It is based on the Harvard

3 System realization
3.1 System overall architecture
The core of the whole system is ADSP2181. A
Windows3.X based monitor program manages the serial
communication between the ADSP2181 and PC. The DSP
executable code and parameters can be downloaded into
ADSP2181 via a serial port. A fast flash ADC(AD9048)
and a fast DAC are included in the system as well. Fig1
indicates the system overall architecture.
3.2 Hardware design and realization
The hardware architecture is indicated in Fig2. As wehave mentioned, there are 512k x 16bit external memory
built in this system. But, we have not directly connectedthe address bus of the RAM and that of the DSP together,as many others did. We add a counter to generate
ADC

ADSP2181

Memory &Control Logic(1)Flexibility. For its real time ability, users can get not
only digital filters but also real filters with digitalflexibility. Many kinds of filters including linear ornonlinear, such as FIR, IIR, multirate, adaptive etc. areeasily implemented.

SPIData

DAC

Latch

Parameters andusers’ DSP
executable fileCOM xAnalogoutDAC
D23Analog
inADSP2181

PC HostThis system is a general purpose digital platform which
can be used in many fields with two main characteristics:
firstly, it can do much processing work at high speed inreal time; secondly it can process mass data in real time.
The Table shows its real time processing ability.
4.2 Applications
Above all, this platform is a high speed DAQ systemwith 16.67MSPS sampling rate and 512k x 16 bit verydeep buffer. Because of the powerful DSP core andexisting DSP algorithms, this system can be applied inmany arenas. We list several applications::/OE

D0/WE/CS
A0..A18M
UX

DecoderParameters
Register

Fig2.

MemoryD0/MW

4.1 Characteristics/MR

4 System characteristics and applications

A13..A0Clockaddresses for the external memory. There are two reasons
why we did this. Firstly, the ADSP2181 can manage only
32k external memory space. If it is beyond this limit, theusers have to use page mode, however, page mode
addressing will slow down the memory access speed and is
not fit for mass data real time processing. Secondly, mostof the real time data processing only needs to access data
sequentially.
By means of address decoding of a DSP external
memory read operation, we can produce a pulse to act as
an ADC sampling pulse and can similarly produce address
counter increasing pulse. Generating these pulses bydecoding makes program timing more feasible and makes
the ADSP2181 and the ADC work synchronously. Thenthe platform is able to do real time mass data sampling
without any additional timing.
For the sake of result observation or feedback control, ahigh speed DAC(AD9700) is included in the system. The
DSP can read a data from internal or external memory andstrobe it into the DAC data latch. Then the DAC converts
the digital signal to an analog signal. The analog signal isdriven to output via a buffer amplifier(AD9617).

:

D8
D7SamplingFig1. Overall architecture of digital platform

D15:
ADC

Address Gen
Counter

Memory Selector

Digital platform hardware blocks

Processing
FIR
IIR(direct)
IIR(cascade)LMS(SG)
PID
ConvolutionAccumulation

Max. Speed in real time (MHz)Single precision Double precision
33/[N+6]
33/[3*N+19]
33/[M+N+12]33/[3*(M+N)+13]
33/[7*N/2+6]
33/[10*N+9]33/[2*N+9]33/[4*N+9]
4.25
33/[N+6]
33/[3*N+19]16.67(512k depth)
0.203ms

FFT(256point,complex)
Table
Maximum real-time processing speed ofgeneral algorithms(2)Digital controllers can be used in servo motor control,
progress control, flight control, general servomechanisms
and so on.
(3)Real time accumulator can be used to accumulatesignals in real time to improve SNR or even extract
periodic signals from heavy noisy background.
(4)Spectral analyzer can be used to study signal spectrum
and can display the spectrum on a computer screen or anoscilloscope.
Of course, others could find more applications in theirown research fields. Here, we would emphasis the realtime accumulation application. It is interesting andeffective. As we know, the SNR of a signal can beimproved 10lg N by means of accumulating the signal Ntimes. Moreover, real time accumulating can extract
period from periodic signals and is especially suit to longperiod signals[6]. For example, a video signal of a still orvery slowly changed scene is a long periodic signal (theframe period is its period). In many cases, a video signal ispolluted by noise for some reasons and the image on
monitor becomes obscure. Like a video signal from a faintlight camera, due to the dark current, noise is relative
heavy, and many “snow” flickers on the monitor screen.
There are thousands of effective image processing methods
which may be utilized to deal with “snow” noise, such as
two dimensional low pass filter, mid-value filter and so on.
But, unfortunately, these methods are all non-real-time.
Because it is simple and easy, accumulating is well suitedfor reducing “snow” noise.
In [7], the authors introduced a two-dimensional image
system based plastic scintillation fiber. It is expected tosubstitute for a traditional detector in biomedical
equipment, industrial CT, custom detector in future. The
read-out subsystem in a faint light camera and the output

isnoisy too. To enhance the image with noise reduction, thedigital platform is able to fully develop its skill.
Reference[1]Analog Device Inc., ADSP-2100 Family User’s
Manual,1993[2]Analog Device Inc., ADSP-2100 Family EZ-KIT Lite
Reference Manual,1995[3]Analog Device Inc., DSP/MSP Products Reference
Manual,1995[4]Analog Device Inc., Using the ADSP-2100 Family
Volume1,1990[5]Analog Device Inc., Using the ADSP-2100 Family
Volume2,199[6]Y. Wang, A Digital Real Time System for Low SNR
Signals Extracting, Master dissertation, Univ. of Sci. &Tech. of China, 1996
[7] XL Wang,ZZ Xu,ZM Wang,HF Chen, A β-ray plastic
scintillation fiber, Nuclear Technique, accepted