Programming the parallel port : interfacing the PC for data acquisition and process control

325 Pages·1998·3.14 MB·English

by  Gadre

Programming
the Parallel Port
Interfacing the PC for Data Acquisition
and Process Control
Dhananjay V. Gadre
CMP Books
Lawrence, KS 66046
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To Chaitanya and Sangeeta
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Foreword
No other interface has been so constant since the PC was introduced in 1981. Origi-
nally implemented to provide a “high speed” interface to the latest generation of dot
matrix and daisy wheel printers, the parallel port has become the most common inter-
face used to connect a wide variety of peripherals.
For many years, up until around 1989, printers were the only peripheral that took
advantage of the parallel port. The port was viewed primarily as a “printer” port and
other types of peripherals did not use it. Then companies such as Microsolutions and
Xircom got the idea that you could actually use the port to get information back into
the computer, and therefore use it as a bi-directional communication port. Being par-
allel, you could get much higher performance than using the PC’s serial port, with
greater simplicity.
The old parallel port became an easy-to-use interface for connecting peripherals.
With a very simple register model, it is easy to get information into and out of the PC.
The only drawback was that it was relatively slow. The CPU and platform perfor-
mance was increasing at a tremendous rate, but the I/O capability of the PC stayed the
same. While the CPU increased 100 fold, the parallel port remained stagnant.
This all changed with the formation of the IEEE 1284 Committee in 1992. This
committee, sponsored by the Institute of Electrical and Electronic Engineers, had the
charter to develop new, advanced parallel port modes that would enable high speed bi-
directional data transfer through the parallel port. The requirements was to do this and
still be 100% compatible with “standard” parallel port. Working with industry groups
and individuals, the IEEE 1284 committee produced its new standard in 1994. This
standard, IEEE St. 1284-1994, defined new ways of using the parallel port for high
speed communication.
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Two of these new modes are the EPP and ECP modes. Now, rather than being lim-
ited to a software-intensive, 50Kb-per-second port, you can get simple data transfer at
rates approaching 2Mb per second. This 40 fold improvement in throughput is even
more remarkable considering that the modes also remain backwards compatible with
existing devices and interfaces.
This standard has enabled a wide range of peripherals that take advantage of the
parallel port. Almost all new peripherals provide support via the parallel port. This
includes the traditional uses such as printers, scanners, CD-ROM, hard drive, port
sharing, and tape, as well as some non-traditional uses.
One of the most popular, non-traditional uses of the 1284 parallel port has been as
a scientific and data acquisition interface. The past few years has seen tremendous
growth in the use of this port for attaching control devices and for use as a simple
interface for data acquisition instruments. The ability to have the same PC interface in
the lab and on every portable computer makes this the ideal port to attach this type of
equipment.
In this book, Interfacing to the PC using the Parallel Port, Dhananjay provides a
clear introduction and model on how to use the parallel port for these types of applica-
tions. This is the ideal reference book for anyone wishing to use the PC for interfacing
to external devices. Dhananjay presents a step-by-step approach to the subject. Start-
ing with the basic, “What is the Parallel Port?” and “What is Data Acquisition”, he
leads you up the path to designing peripheral interfaces and writing the software driv-
ers necessary to control and communicate with your devices.
I’m sure you’ll find this an invaluable tool in aiding your understanding of the par-
allel port and the concepts and implementations of data acquisition peripherals.
Larry A. Stein
Larry Stein is the Chair of IEEE 1284.3 and 1284.4 Committees. He was instru-
mental in the development of the IEE 1284 standard and served as chair of the EPP
Committee. He is currently Vice-President of Warp Nine Engineering and is the chief
architect of the Warp Nine interface cards and IEEE 1284 Peripheral Interface Con-
troller.
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Acknowledgments
My interest in parallel printer adapters began in 19980 when Professor Vijaya Shan-
kar Varma at the Delhi University asked me if I could build a resistor DAC for the par-
allel port. Since then, together with Dr. Pramod Upadhyay, we have enjoyed building
and using many devices on the parallel port. It has been a pleasure working with
them. Most of these gadgets were built at the Centre for Science Education and Com-
munication (CSEC), University of Delhi.
While we were at it, Professor Pramod Srivastava, Director of CSEC, was a con-
stant source of suggestions and useful comments. He was an even bigger help in pro-
viding financial support for the projects.
Since coming to the Inter-University Centre for Astronomy and Astrophysics
(IUCAA) in Pune, India, Pravin Chordia has been a great help in building many of the
devices. Arvind Paranjpye suggested the photometer interface problem, which was
completed as another project. Manjiri Deshpande provided useful suggestions and
evaluated some of the ideas presented here.
Professor S.N. Tandon, my boss at the Instrumentation Laboratory, allowed me to
use the facilities in the laboratory for building many of the projects described here.
Working with him has been an education for me and I thank him for many of the
things I learned from him.
I learned the finer points of UNIX and Linux from Sunu Engineer. A brilliant pro-
grammer that he is, all the Linux-related projects would have been incomplete with-
out his collaboration. He also read through many of the chapters in this manuscript
and provided critical comments.
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This work has been possible, in no small measure, because of the atmosphere of
academic freedom I enjoy at IUCAA, and I thank Professor J.V. Narlikar, Director of
IUCAA, for creating this wonderful place and providing me with a chance to work
here.
Thanks are due to Dr. James Matey, Contributing Editor of Computers in Physics;
to Joan Lynch, Managing Editor of EDN; to Jon Erickson, Editor-in-Chief of Dr.
Dobb’s Journal; and to Lindsey Vereen, Editor-in-Chief of Embedded Systems Pro-
gramming; for providing me the opportunities to write for their respective journals.
I thank Jon Erickson (DDJ), Mike Markowitz (EDN), and Lindsey Vereen (ESP),
for allowing me to use the material from their respective journals for this book.
Larry Stein, of Warp Nine Engineering and Chairman of IEEE’s P1284 commit-
tee, was a great help in providing details about the EPP and ECP, and I thank him for
that.
Thanks are also due to Santosh Khadilkar for his help in organizing the manu-
script for this book. This manuscript was prepared using the IUCAA computer centre
facilities.
I am delighted to thank my wife, Sangeeta, for her encouragement and her
patience. She fought like a lone warrior in engaging and containing our son, Chait-
anya, while I was busy. It was only because of her support that this work could be
undertaken, and I cannot thank her enough.
This acknowledgment would be incomplete without placing on record my deep
sense of gratitude to the foresight of my parents, Aai and Nana, in providing me a
decent education even in the face of severe financial crunch. I think nobody else
would be happier than Aai and Nana in seeing this book in print.
Dhananjay V. Gadre
Pune, India
Dhananjay Gadre is a Scientific Officer with the Instrumentation Programme of
the Inter-University Centre for Astronomy and Astrophysics, Pune, India. He has been
working with the IUCAA for the past four years. Previously, he was a lecturer at the
SGTB Khalsa College, University of Delhi, teaching undergraduate electronics for
about four years. He is now a graduate student at the Microelectronics Research and
Communications Institute, Electrical Engineering Department, University of Idaho,
on study leave from IUCAA.
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Table of Contents
Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
Chapter 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Why the Parallel Port?....................................................................1
What is Data Acquisition?..............................................................2
Intended Audience..........................................................................3
Organization of the Book................................................................4
Companion Code on the FTP Site...................................................6
Chapter 2 How to Build a Computer Interface . . . . . . . . . . . . . . 7
What is an Interface?.......................................................................7
Examples of Various Schemes for Data Acquisition......................7
A Speech Digitizer..........................................................................8
Data Acquisition for a CCD Camera............................................11
Signal and Timing Diagram Conventions.....................................14
Hardware Components..................................................................15
Digital Components......................................................................20
Chapter 3 The Parallel Printer Adapter. . . . . . . . . . . . . . . . . . . 25
Anatomy of the Parallel Printer Port.............................................26
The DATA Port.............................................................................29
The CONTROL Port.....................................................................31
The STATUS Port.........................................................................33
Printing with the Parallel Adapter.................................................36
Using the Parallel Printer Adapter................................................37
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