The task of upgrading one of the best introductory and authentic texts in the field of Digital
Electronics, in its newest edition, is as much a challenge as a matter of pride. The job was to build
upon the strength of the earlier edition -- its simple lucid language, down to earth approach, clear
detailed analysis and ready-to-use information for laboratory practices at appropriate places. This
edition sought improvement primarily by (i) strengthening the design or synthesis aspect and
(ii) including new materials like Hardware Description Language (HDL), Asynchronous Sequential
Circuit, etc. that have come up recently and are changing the way Digital Electronics is taught at
various places. Two new chapters, one on 'Design of Sequential Circuit' and the other on 'Simple
Computer Design' have been added. Instead of having a separate new chapter on HDL, relevant
concepts have been added at the end of the each chapter. Minor improvements have been made in
other chapters too, wherever it was found necessary.
A SUMMARY OF THE CHANGES
A summary of how each chapter is strengthened in this edition is as follows.
In Chapter 1, a reference to 'Optical Memory' has been added which is an integral part of modern
Digital System.
In Chapter 2, the universality of NAND and NOR logic is discussed in detail.
In Chapter 3, the concept of Entered Variable Map is introduced which is useful in simplifying
logic expressions in lower dimension space. Conversion between Sum-of-Product and Product-of-
Sum form, useful from implementation point of view, is also discussed. Logic minimization using
Quine-McClusky method is discussed which is useful for minimization of five or more variables and
for its ease in the form of a computer code. The accompanying Web site of the book makes this
code available for the user of this book. The concept of Hazards occurring in digital circuits and
solution to that in the form of Hazard Covers have been discussed in detail.
In Chapter 4, the topic Multiplexer and Demultiplexers are rewritten with the inclusion of new
ideas and examples. The concepts of Priority Encoder and Magnitude Comparator, which are useful
combinatorial circuits, have been introduced.
In Chapter 5, the concept of Gray Code and its conversion to and from Binary Code has been
discussed. Gray Code finds useful application in the industry in coding sensor outputs.
In Chapter 6, the concept of Fast Adder or Look Ahead Carry Adder have been introduced which
gives the reader an idea about the trade-off between simplicity and speed, at which a circuit operates.
Arithmetic Logic Unit, a versatile device capable of both Arithmetic and Logic operations is also
discussed.
In Chapter 8, various representations of Flip-Flops have been included in the form of
characteristic equation, excitation table, state transition diagram. Conversion between one type of
flip-flop to the other is discussed as a synthesis example. Analysis of sequential circuit where flipflop
is a key element is also introduced in this chapter.
Chapter 9 now includes new applications of Shift Registers as sequence generator-detector, serial
adder, etc.
In Chapter 10, synchronous counter design has been introduced as a synthesis problem. Issues like
lock-out and its avoidance have also been introduced. Use of Counter in sequence generation is
discussed with an example.
Chapter 11, new to this edition, discusses different issues of sequential logic design—both
synchronous and asynchronous. Concepts of Moore Model, Mealy Model and their conversion have
been introduced. Algorithmic State Machine chart has been introduced as design development tool
and a simple implementation technique using Read-Only-Memory and Delay Flip-Flop is also
discussed. Introductory material on state reduction technique has been included.
Chapter 13, Magnetic Memory is rewritten to make it contemporary. Optical Memory and
Sequential Programmable Logic Devices, like PLD(Programmable Logic Device), CPLD(Complex
Programmable Logic Device) and FPGA(Field Programmable Gate Array) have been discussed.
Chapter 16, a new Chapter that intends to take the reader to the next level where one can think
of designing a simple computer from the fundamentals. It makes the reader identify the required
hardware building blocks, develop its data path and control unit and also the way to program the
machine developed, for various computing problems.
In Chapters 7, 12, 14 and 15, only minor modifications have been incorporated.
Note that, text and illustration added to describe HDL is equivalent to a new Chapter but it is
scattered throughout the book to introduce the concepts relevant to a particular topic. It also discusses
in detail how to prepare simulation test bench and shows simulation outputs through various
examples. More material on this is available on accompanying Web site where actual outputs on
Xilinx FPGA has been shown in the form of screen shots.
ONLINE LEARNING CENTRE
The accompanying Web site, http://www.mhhe.com/leach/dpa6 designed to be an Online Learning
Centre (OLC) is an important addition to this edition. Besides Quine-McClusky code and HDL
example, additional information and discussion on various supplementary materials like five variable
Karnaugh Map, Error detection and correction, etc. will be available here. Regular updates on
different topics of Digital Electronics will be posted to keep the reader updated about recent changes
in this field. The instructors who adopt this as textbook will have a password protected section
providing lecture slides and solutions to all the problems in the book. Care has been taken to avoid
any mistake in the print edition as well as in the OLC. However, any note on oversight, if any, will
be gratefully received as also all suggestions for further improvement.
ACKNOWLEDGEMENTS
First of all I would like to acknowledge the inspiration and help I received from Prof. (Retd.)
B. N. Chatterji, Prof. R. N. Pal, Prof. R. V. Rajakumar, Prof. P. P. Chakraborti,
Prof. A. Chakraborty, Prof. S. Sengupta, Prof. P. K. Biswas, Prof. A. K. Roy, Prof. S. Bannerjee,
Prof. I. Chakraborti, Prof. P. Mandal and all my faculty colleagues at Indian Institute of Technology
(IIT), Kharagapur. But for the paucity of the space, I would have named many others.
Thanks are due to my research students Mr. S Ari, Mr. P. Pattadar, Mr. S. Chakraborti, Mr. S.
Senapati for their help in different stages of development of the book. I acknowledge the benefit
derived from my interaction with different batches of students in the last seven years of teaching
Digital Electronics, three years in the Institute of Engineering and Management, Salt Lake, Kolkata
and four years, here at IIT Kharagpur. The feedback and help I received from Mr. R. Rithe, Mr.
S. Sen, Mr. M. Kishore, Mr. S. Maheshwaran, Ms. S. Srivastava and others of the current batch have
been very useful.
I am grateful to the following reviewers for their encouraging comments and valuable suggestions
for this edition.
1. Prof. S. Rathnavel, Assistant Professor, Department of ECE, Dr. Mahalingam College of
Engineering & Technology, Pollachi, Coimbatore.
2. Ms. Sheeba Rani, Assistant Professor, ECE Department, Noorul Islam Engineering College,
Kumaracoil, Thuckalay, Nagercoil.
3. Dr. D. Ranga Rao, Associate Professor, Department of Electronics & Communication
Engineering, University College of Engineering, Osmania University, Hyderabad.
4. Mrs. J. P. Anuradha, Assistant Professor, Department of Electronics & Communication
Engineering, SJM Institute of Technology Chitradurga.
5. Adarsh R. Kordcal, Department of Computer Science & Engineering Manipal Institute of
Technology.
6. Prof. V. G. Sarode, Department of Computer Science and Engineering, Atharva College of
Engineering, Navi Mumbai.
7. Dr. J. Deka, Assistant Professor, Department of Computer Science and Engineering, Indian
Institute of Technology, Guwahati.
8. Dr. Amitabha Sinha, professor, Department of Computer Science and Engineering, WBUT,
Kolkata.
9. Dr. Asim Jana, Assistant Professor, Department of Electronics & Communication Engineering,
Haldia Institute of Technology, Haldia.
10. Prof. K. S. Srinivasan, Professor/Head, Department of Electronics, Sathyabama Deemed
University, Chennai.
I also thank the entire publishing team, more specifically Mr. Jacob Alexander who had been a
tower of patience and instrumental in getting the work done by me, Ms. Vibha Mahajan who initiated
this work in one of her IIT Khargpur visits, Ms. Mini Narayanan for copyediting and Ms Anjali
Razdan for proof reading and Mr. Baldev Raj for the OLC development, for their support. At this point, I humbly remember all my teachers and my father (late) G. N. Saha and uncle (late)
S. Sadhukhan. Last but not the least, I must mention the help and support I received from my
family—my mother, my parents-in-law, my wife Sanghita and my daughter Upasana—in the course
of writing this book over a period of eighteen months. The effort behind this edition was mine but
the time was all theirs.
GOUTAM SAHA
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2006
Tata McGraw-Hill