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Digital logic techniques
feasibility studies. This is further supported by some of the choices of microcomputer, eg Apple II, Commodore 32, Epson HX20 and TI9900. Admirable though these machines may be for many purposes, they would not normally be first choice for embedded computer industrial applications. The one paper which describes all three aspects (ie application, design philosophy and problems, and microcomputer system design and implementation) adequately is 'A microprocessor based hydrostatic steer control for a main battle tank' by Hislop and Gibson. Even here the microprocessor system design and implementation is not covered in sufficient detail to assist anyone considering going down this path. Also it would have been nice to know more about a system using an 8086 and 8087 processor, and using Coral 66 with a Mascot kernel.
The other two papers which are considered adequate to meet the requirements of Microprocessors in fluid power engineering are 'The utilization of a microcomputer in the condition monitoring of a hydraulic pump' by Hunt, Barker and Prest and 'A modular microprocessor data acquisition system for hydraulic pump research' by Prest and Barker. It is interesting to note that, in these three cases, one of the collaborators is an electronics- or computer-oriented person. This illustrates yet again the point that there is a need for collaboration between the disciplines. Although a staggering thought, it is not new. Some years ago a conference on medical electronics was held at which members of the lEE promised not to treat sick people if the doctors would stop designing electronic circuits. Now although computer systems
engineers would not attempt to design hydraulic control valves, at least this one would not, some fluid power engineers are quite happy to design and i m p l e m e n t microcomputer systems. Mechanical engineers and other n o n m i c r o c o m p u t e r system engi~ neers reading this publication will gain knowledge in what people think can be done, or are trying to do, in applying microcomputers to fluid power. However, they will learn little about applying microprocessors, or the problems in doing so. Microcomputer systems engineers will learn nothing about applying microcomputers but will certainly have their attention drawn to a number of interesting application areas which might benefit from their attentions.
Joe Gallacher Microprocessor Systems Engineering Ltd, UK
Tutorial stresses the advantages of taldng a 'systm,,s approach' T I Stoneham
"Digital logic techniques' Van Nostrand Reinhold, UK (1984) £5.75 pp 742 This book is the newest in a series of publications entitled Tutorial
guides in electronic engineering. The series is aimed at first- and second-year engineering undergraduates and is intended to promote a 'systems' approach to engineering design. In this book, the reader is introduced to combinational and sequential logic design techniques before being led onto some features of digital system design. The final chapter deals with practical circuit contraints. The general presentation of this book is extremely good; it is easy to read and topics are introduced in a well ordered manner, building on techniques developed earlier in the book. Unlike many of its predecessors, great emphasis is placed on the practical significance
34
of circuits and systems. This is reinforged by using worked examples throughout the text, which reduce the need for lengthy descriptions and additionally provide the reader with a great deal of useful insight into design techniques. I also found the use of marginal notes to be an interesting feature. These are used effectively to clarify symbols or abbreviations in the text or to reproduce information derived earlier in the book for the convenience of the reader. My only dislike of the general presentation was the way in which exercises have been included in the middle of the text (without answers). These often break up the flow of the text and seem particularly unnecessary as the author has included problems at the end of each chapter (with answers), in addition to the worked examples. The sections on combinational and sequential logic concentrate on the use of Karnaugh maps and present/next state tables to define and minimize circuit action. In addition to using these tools to
advantage in many of the worked examples, the author also indicates areas where excessive minimization is not a worthwhile task; this matter is often overlooked in texts of this kind. However, one major criticism of the book, which is particularly valid in these sections, is that there is a grave lack of external referencing. The only references that appear are included as marginal notes and nearly always refer to other Van Nostrand books; many interesting topics are referred to by author's name alone, without completing the reference. In view of the target readership, I feel that this is a rather serious omission. The sections of the book which deal with digital systems and practical circuitry make extremely good reading. It is a pleasure to see a book on logic circuits get away from mere gate implementation of logic functions and to address some of the interesting techniques for realizing programmable logic using memories and registers. These days memory elements are cheap and plentiful, and their use in performing logic
microprocessors and microsystems
functions offers an attractive and cost-effective solution to many problems. I was also pleased to see rather more than lip-service paid to the problems of testing logic circuits, which is becoming an increasingly important subject in these days of VLSI. The author clearly has experience of circuit design in a number of different areas, and his comparisons of technologies and techniques make interesting reading. It is good to see an emphasis on
integrated circuit realizations, and a section written on programmable logic arrays, but I would have thought that mask programmable gate array circuits would also have been worthy of a mention. I was reasonably impressed with the accuracy of the written script. It is not bugged with errors and, although I spotted one or two typographical errors throughout the text, few will lead the reader astray. The author has clearly tried to use simple mathematical notations
where possible, and this will no doubt be appreciated by the intended readership. Despite being bound in a soft cover which may not stand up too well to the hazardous student environment, at £5.75 the book clearly represents good value for money. Overall, I was impressed with the book and would expect to see it used widely on undergraduate courses.
P Challener British Telecom plc
Useful background information for novice programmers on Acorn micros Clive Williamson "Getting the most from your Acorn Electron' Penguin, UK (?984) £6.95 pp 173 'Getting the most from your BBC Micro' Penguin, UK (1984) £5.95 pp 208 The Electron was effectively derived from the BBC machine; it runs the same BASIC language and has a very similar operating system. It is perhaps not surprising therefore that both these books are very similar in content, differing only in the minor machine details. What is more surprising is the fact that the Electron version of the book (at £6.95) is more expensive than the BBC version (£5.95), despite the latter book's extra length. The author states that the books are 'intended to complement the User Guide supplied with the machine'. In this he succeeds for the most part, although he does not make it quite clear whether they are aimed atthe complete beginner or the more experienced user. The statement that he intends to explore the 'potential for expansion to suit each owner's particular needs' is somewhat vague as the home-computer user is a complex animal, and it would need to be a great deal more imposing and detailed piece of work in order to cover every aspect of this ideal/ aim. The main problem is that the author tries to be all things to all men/women by covering a wide
vol 9 no I jan~feb 1985
variety of topics in less than 200 pages. Consequently, the depth of coverage varies enormously from subject to subject. This can be rather confusing for the beginner, who is probably the user most likely to be interested in and to benefit from the books. For instance, although small businesses are mentioned specifically in the BBC Micro book there is very little detailed information on the suitability of the BBC machines for business use. The initial emphasis on filestore is on cassette recorders, and disc drives are only included towards the end. There is also no critique of the disc filing system used in the BBC machine. The Electron ~,ersion of the book is more explicit and emphasizes its domestic use. The current expansion available for the Electron is the Plus 1 which gives a joystick, cartridge and a printer interface. In future expansion the facilities currently available on the BBC only are described. The early parts of the books on BASIC programming give useful examples to the novice but suffer from the drawback that the 'structured' features of BBC BASIC are introduced as an afterthought rather than as an integral part from the beginning. An illustration of this is the discussion on subroutines where GOSUBs are introduced in some detail and freely used in the examples. One of the main features of BBC BASIC is that it is a modern structured BASIC and this should have been emphasized.
The general discussion on the building blocks of a microcomputer will provide useful background information to the novice programmer. However, there is no mention made of the assembler built intothe BBC BASICsystem.This could have been used to provide small examples of the central processor's operation. The pace accelerates towards the end of the books: peripherals and expansion are covered in a hurried fashion. One example of this is the description of eight languages in less than two pages. All that can be given in this space is some indication of what is currently available. One important feature of any book is the index, conspicuous by its absence in both these works. Its omission makes any reference much more difficult to obtain, and in both these books causes irritation, especially if the reader is a beginner in the field and is a bit overwhelmed by the technical jargon. On the plus side there are some useful appendices included in both books, plus a short further reading list. On the whole, the author writes in a pleasing and easy style, and the illustrations and diagrams are attractively arranged and reasonably clear. The books certainly fill in some of the gaps indicated and provide useful background information. G W Smethurst University of Keele, UK
35
The other two papers which are considered adequate to meet the requirements of Microprocessors in fluid power engineering are 'The utilization of a microcomputer in the condition monitoring of a hydraulic pump' by Hunt, Barker and Prest and 'A modular microprocessor data acquisition system for hydraulic pump research' by Prest and Barker. It is interesting to note that, in these three cases, one of the collaborators is an electronics- or computer-oriented person. This illustrates yet again the point that there is a need for collaboration between the disciplines. Although a staggering thought, it is not new. Some years ago a conference on medical electronics was held at which members of the lEE promised not to treat sick people if the doctors would stop designing electronic circuits. Now although computer systems
engineers would not attempt to design hydraulic control valves, at least this one would not, some fluid power engineers are quite happy to design and i m p l e m e n t microcomputer systems. Mechanical engineers and other n o n m i c r o c o m p u t e r system engi~ neers reading this publication will gain knowledge in what people think can be done, or are trying to do, in applying microcomputers to fluid power. However, they will learn little about applying microprocessors, or the problems in doing so. Microcomputer systems engineers will learn nothing about applying microcomputers but will certainly have their attention drawn to a number of interesting application areas which might benefit from their attentions.
Joe Gallacher Microprocessor Systems Engineering Ltd, UK
Tutorial stresses the advantages of taldng a 'systm,,s approach' T I Stoneham
"Digital logic techniques' Van Nostrand Reinhold, UK (1984) £5.75 pp 742 This book is the newest in a series of publications entitled Tutorial
guides in electronic engineering. The series is aimed at first- and second-year engineering undergraduates and is intended to promote a 'systems' approach to engineering design. In this book, the reader is introduced to combinational and sequential logic design techniques before being led onto some features of digital system design. The final chapter deals with practical circuit contraints. The general presentation of this book is extremely good; it is easy to read and topics are introduced in a well ordered manner, building on techniques developed earlier in the book. Unlike many of its predecessors, great emphasis is placed on the practical significance
34
of circuits and systems. This is reinforged by using worked examples throughout the text, which reduce the need for lengthy descriptions and additionally provide the reader with a great deal of useful insight into design techniques. I also found the use of marginal notes to be an interesting feature. These are used effectively to clarify symbols or abbreviations in the text or to reproduce information derived earlier in the book for the convenience of the reader. My only dislike of the general presentation was the way in which exercises have been included in the middle of the text (without answers). These often break up the flow of the text and seem particularly unnecessary as the author has included problems at the end of each chapter (with answers), in addition to the worked examples. The sections on combinational and sequential logic concentrate on the use of Karnaugh maps and present/next state tables to define and minimize circuit action. In addition to using these tools to
advantage in many of the worked examples, the author also indicates areas where excessive minimization is not a worthwhile task; this matter is often overlooked in texts of this kind. However, one major criticism of the book, which is particularly valid in these sections, is that there is a grave lack of external referencing. The only references that appear are included as marginal notes and nearly always refer to other Van Nostrand books; many interesting topics are referred to by author's name alone, without completing the reference. In view of the target readership, I feel that this is a rather serious omission. The sections of the book which deal with digital systems and practical circuitry make extremely good reading. It is a pleasure to see a book on logic circuits get away from mere gate implementation of logic functions and to address some of the interesting techniques for realizing programmable logic using memories and registers. These days memory elements are cheap and plentiful, and their use in performing logic
microprocessors and microsystems
functions offers an attractive and cost-effective solution to many problems. I was also pleased to see rather more than lip-service paid to the problems of testing logic circuits, which is becoming an increasingly important subject in these days of VLSI. The author clearly has experience of circuit design in a number of different areas, and his comparisons of technologies and techniques make interesting reading. It is good to see an emphasis on
integrated circuit realizations, and a section written on programmable logic arrays, but I would have thought that mask programmable gate array circuits would also have been worthy of a mention. I was reasonably impressed with the accuracy of the written script. It is not bugged with errors and, although I spotted one or two typographical errors throughout the text, few will lead the reader astray. The author has clearly tried to use simple mathematical notations
where possible, and this will no doubt be appreciated by the intended readership. Despite being bound in a soft cover which may not stand up too well to the hazardous student environment, at £5.75 the book clearly represents good value for money. Overall, I was impressed with the book and would expect to see it used widely on undergraduate courses.
P Challener British Telecom plc
Useful background information for novice programmers on Acorn micros Clive Williamson "Getting the most from your Acorn Electron' Penguin, UK (?984) £6.95 pp 173 'Getting the most from your BBC Micro' Penguin, UK (1984) £5.95 pp 208 The Electron was effectively derived from the BBC machine; it runs the same BASIC language and has a very similar operating system. It is perhaps not surprising therefore that both these books are very similar in content, differing only in the minor machine details. What is more surprising is the fact that the Electron version of the book (at £6.95) is more expensive than the BBC version (£5.95), despite the latter book's extra length. The author states that the books are 'intended to complement the User Guide supplied with the machine'. In this he succeeds for the most part, although he does not make it quite clear whether they are aimed atthe complete beginner or the more experienced user. The statement that he intends to explore the 'potential for expansion to suit each owner's particular needs' is somewhat vague as the home-computer user is a complex animal, and it would need to be a great deal more imposing and detailed piece of work in order to cover every aspect of this ideal/ aim. The main problem is that the author tries to be all things to all men/women by covering a wide
vol 9 no I jan~feb 1985
variety of topics in less than 200 pages. Consequently, the depth of coverage varies enormously from subject to subject. This can be rather confusing for the beginner, who is probably the user most likely to be interested in and to benefit from the books. For instance, although small businesses are mentioned specifically in the BBC Micro book there is very little detailed information on the suitability of the BBC machines for business use. The initial emphasis on filestore is on cassette recorders, and disc drives are only included towards the end. There is also no critique of the disc filing system used in the BBC machine. The Electron ~,ersion of the book is more explicit and emphasizes its domestic use. The current expansion available for the Electron is the Plus 1 which gives a joystick, cartridge and a printer interface. In future expansion the facilities currently available on the BBC only are described. The early parts of the books on BASIC programming give useful examples to the novice but suffer from the drawback that the 'structured' features of BBC BASIC are introduced as an afterthought rather than as an integral part from the beginning. An illustration of this is the discussion on subroutines where GOSUBs are introduced in some detail and freely used in the examples. One of the main features of BBC BASIC is that it is a modern structured BASIC and this should have been emphasized.
The general discussion on the building blocks of a microcomputer will provide useful background information to the novice programmer. However, there is no mention made of the assembler built intothe BBC BASICsystem.This could have been used to provide small examples of the central processor's operation. The pace accelerates towards the end of the books: peripherals and expansion are covered in a hurried fashion. One example of this is the description of eight languages in less than two pages. All that can be given in this space is some indication of what is currently available. One important feature of any book is the index, conspicuous by its absence in both these works. Its omission makes any reference much more difficult to obtain, and in both these books causes irritation, especially if the reader is a beginner in the field and is a bit overwhelmed by the technical jargon. On the plus side there are some useful appendices included in both books, plus a short further reading list. On the whole, the author writes in a pleasing and easy style, and the illustrations and diagrams are attractively arranged and reasonably clear. The books certainly fill in some of the gaps indicated and provide useful background information. G W Smethurst University of Keele, UK
35