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BOOKSHELF Handy reference on microcomputer interfacing & applications Microcomputer Interfacing and Applications, M. A. Mustafa, published January 1995 by Newnes. Soft covers, 233 x 155mm, 456 pages. ISBN 0 7506 1752 7. Price $69.00. This is the second edition of this book which, in its 17 chapters, reasonably fully covers all aspects of the operation and interfacing of micros to the outside world. The first chapter is pitched at the beginner who is assumed to have little or no knowledge of the subject. It covers proces­sors, storage devices, input/output (I/O) devices, microprocessor operation, task execution and interrupts. Chapter two explains why external devices may need to be connected to a microcomputer, the methods used to communicate with these devices and the concept of input and output ports. The next chapter expands on this by discussing the need for flexibility in and optimisation of any add-ons that you may use. The boards which are described are mostly for the IBM style computer and its clones, mainly because of the diverse range of offthe-shelf boards which have become available for this type of computer. Mustafa then goes on to compare the pros and cons of inter­rupt versus program controlled output. The chapter concludes with a few examples of the decoding of external address spaces. Chapter four, entitled Using Digital Input and Output Ports, begins by showing the methods used to detect external switch closures and includes a discussion on switch debounce using both hardware and software. It continues by explaining how comparators 38  Silicon Chip can be used to indicate out of tolerance voltages. Hardware logic gates are covered next, followed by an explanation of how the various gates can be implemented in soft­ware if there are sufficient processor input lines available. Most of the balance of the chapter is taken up with the solutions to various problems, using both hardware and software approaches. The last 10 pages of this chapter discuss AC, inductive loads and power factor. Chapters five to eight cover, in great detail, Multiplexers, Sample and Hold circuits, and Digital to Analog (D/A) and Analog to Digital (A/D) converters. This information will be familiar to the experienced hobbyist or engineer but should prove enlighten­ing to the novice. Chapter six explains how D/A converters can be interfaced to a microprocessor and chapter seven does the same for A/D converters. Chapter eight details the application of several commercial devices to the solutions of some hypothetical prob­lems. The next chapter covers external counters and timers, although most modern micros now seem to include these on the chip. Still it is often easier to implement counting or timing functions in hardware using an interrupt, than in software, as these functions can occupy a large percentage of the processor’s time. Applications using several timers, including that old fa­vourite the 555, are shown. Methods of measuring frequency, time intervals and phase shifts are examined, almost always using external hardware to process the input signals. Chapter 10 diverges from micros to discuss switching devic­es, although the ultimate end is to control these via a computer. Diodes, zeners, transistors, FETs, MOSFETs, IGBTs, SCRs, thyris­ tors, Triacs and relays are all included in this summary. The important subject of isolating control circuits from the mains supply is adequately covered. The next chapter, titled Optical Devices, is a continuation of the previous one. It covers light sensing devices such as photodiodes, photo­ transistors, light dependent resistors and light emitting devices such as opto-couplers, light emitting diodes (LEDs) and 7-segment LED displays. Methods of interfacing these different devices to micros are shown and an explanation is given of the way LED displays are multiplexed. The chapter concludes with nearly nine pages which cover optical encoders. The incremental encoder is widely used but suffers from the problem that it can only count pulses but cannot give any absolute position. To increase their usefulness, modifi­ cations have been made such as an extra output providing one pulse per revolution at a predetermined position. Absolute encoders overcome the previous problems by repre­ senting each position by a unique code but this obviously will require more input data lines to a processor. Chapter 12 explains how to generate waveforms, again by utilising either software or hardware under computer control. Mustafa begins this chapter by discussing the types of waveforms that are usually generated by hardware, then compares the pros and cons of real time calculations versus look-up tables. He continues with examples of the generation of different waveforms using both digital and analog interfaces for frequency selection. The chapter also shows how DC offsets can be generated and added to the output waveform. The 13th chapter introduces us to microcomputer controlled robotic mechanisms. Both analog and digital, open and closed loop controls are covered. While the chapter is quite comprehensive, the robot designers will know it all and the hobbyist is unlikely to begin designing robots after reading it. Temperature measurement and control is the heading for chapter 14. The various types of sensors including thermistors, thermocouples, RTDs (resistance temperature detectors) and semi­conductors are explained. The methods used to control the temperature once it has been sensed are then described. These are on/off, pulse width, phase angle and zero crossing switching. Some examples of these methods are then given. A chapter on motor control is next. Many industrial process control systems will, as part of their task, control the speed of a motor. As we know there are two types of motors, DC and Practical Guide to Satellite TV The Practical Guide to Satellite TV, by Garry Cratt. Pub­ lished February 1997. ISBN 0 646 30682 0. 296 x 210mm, soft covers, 116 pages. R.R.P. $39.00. Published in February this year, this easy-to-read book has been compiled by one of the most experienced satellite TV in­stallers in Australia, Garry Cratt. It is written in an informal style and is copiously illustrated. Topics covered include a history of satellite development, principles of satellite operation, earth station components, encryption systems, video stan­ dards, video compression (MPEG, etc), system installation and wiring. As you might expect, there is a lot of information about satellite receiver hardware such as dishes, feedhorns, polaris­ers, LNBs (low noise block converter) and so on. There is a large glossary and 46 pages of satellite orbital data, transponder loading and footprints. AC and they, unfortunately, require different methods of control. The author describes the various types of DC motor speed control using the computer in a closed loop system, then other methods which use some external hardware but don’t take as much computer processing time. The speed of an AC motor can be varied by altering either the applied voltage or the applied frequency. While the latter is harder to implement, it is the more efficient method, as the output torque is higher. Various methods using voltage, frequency and pulse width to vary the motor speed are then described. The penultimate chapter, headed Miscellaneous Applications, covers such things as interfacing a keypad to a micro, interrupt control, DMA (direct memory access) and handshaking. It continues by discussing rudimentary process control test procedures, the provision of additional supplies to power the external add-ons and battery backup of these add-ons. The final chapter talks about the In summary, this book is down to earth and up to date. It is available at $39.00 plus $5 postage from Av-Comm Pty Ltd, PO Box 225, Balgowlah, NSW 2093. Phone (02) 9949 7417; fax (02) 9949 7095. possible limitations of an existing computer system and the upgrade paths available. It also describes the limited storage of RAM and the probable need to transfer RAM data to a hard disc. Brief mention is then made of operating systems, programming languages and emulators. An emulator is a collection of hardware which allows a software program (eg, for a microcontroller) to be loaded into it and executed. The program steps can be traced and intermediate values checked to confirm the correct operation of the program before it is “burned” into the final device. If “bugs” are found, the program can be altered then run again to verify its correct operation. To sum up, this book is a good reference for the hobbyist or student who wants to have a better understanding of the topics covered. It contains lots of worked examples to illustrate each chapter and is an ideal starting point. Our review copy came from Reed International Books Austra­lia Pty Ltd. Phone (03) 9245 7168. (R.F.W.) SC April 1997  39