BOOK: COMPUTER INTERFACING TECHNIQUES
IN SCIENCE
BY: PAUL FIELD & JOHN DAVIES
FROM: SCOTT, FORESMAN & CO. - 1900 E.
LAKE AVENUE, GLENVIEW, IL 60025
(312) 729-3000
PRICE: $12.95
“Computer Interfacing Techniques in Science” contains some 30 experiments for use on any ZX computer (ZX81, TS1000, 1500, Spectrum or TS2068). It is definitely not for the rank beginners to interfacing circuiting, but can serve as a good “second-book” for those who already have some circuit-building skills and wish to expand their horizons.
The book is comprised of 7 chapters and 4 Appendices, one of which is a unique, if awkward to use, cut-out and paste-up manual assembler device. The main thrust of the book is, as the title suggests, for technicians, scientists and teachers as well as hobbyists. It is clearly intended to serve as a sort of lab manual for hardware experiments.
The preface and chapter I give very general background information about computers and number systems in general. Brief mention of TS/ZX computers is made. Chapter II is a crash course in digital logic, from simple AND, OR gates up through the more complex decoders, counters and timers. It is also in Chapter II that we begin to realize that this book is definitely not for the novice.
As the authors begin to address “Hardware & Tools”, and Breadboarding, we find no photographs or sketches of hardware (save one sketch of blank breadboard) or tools. A very cursory look at construction techniques is soon followed by the biggest disappointment of the book: the authors specify the purchase of the FDZX1 interface board. This means that if you want to do these experiments, you’ll probably need to purchase that board. The address of the vendor, Group Technology, LTD, Box 87, Check, VA 24072, is given. You’ll probably have time to order the board though, since it (and the computer as well for that matter) is not needed for the first 6 experiments. The experiments are well thought out and given just a few relatively common TTL IC’s, a garden variety solderless breadboard, and some prior knowledge on the use of same, the average reader should be able to experiment with and begin to understand basic logic circuits.
In Chapter III, the system buses and their uses are discussed and a fast reference to machine code programming is given. Interestingly, to maintain compatibility in software between the TS1000 and 2000 series the author has not used the IN and OUT BASIC commands of the latter. This means you must use a USR call in either machine. The “experiments” in this chapter involve inputting machine code bytes and running short programs which illustrate the 8080 instruction set.
Chapter IV begins with a statement that there are 256 I/O ports. In fact, with extended addresses (use the BC pair) there can be over 65000 I/O ports. The authors may be simply trying not to confuse the reader at this point. Parameters for I/O ports, gating, addressing and timing are discussed and finally a schematic for the buffered interface circuit is given. Here, for the first time, you’ll need your interface as well as breadboard to conduct such experiments as creating a device select pulse, setting up simple input and output ports and preparing an advanced I/O port using the 8255 P.P.I.
Finally, in Chapter V, we get to the real meat of the book. The authors at first generalize (e.g. a serial-to-parallel conversion circuit is discussed, but not realized), but soon get down to serious interfacing. The first experiment here gives the circuit and software for an effective analog joystick interface using 555 timers and simple “pot” type joystick (e.g. Radio Shack, Apple). A real time clock is built and programmed (58167) or 53167 IC – one of the few typos in the book. A “dead end” RS232 port is built. This port can only talk to itself and is thus of limited usefulness except for instructional purposes.
Analog Conversions are covered in more detail in Chapter VI. Light sensitive devices, an electronic scale, temperature measuring and control are demonstrated in these experiments. Again, a sound experimental technique is followed and the serious hobbyist or student will get much from these lab trials.
Overall, I found “C.I.T. in S.” delivered valuable instruction and information. It would serve well as a supplemental book to “Powerful Projects” (reviewed elsewhere) from the same publishers, and I’m certainly not unhappy that I purchased the book.
However, as with many such works it is seriously flawed in not delivering all that is promised. You’re not told until page 28, in one sentence, that you aren’t going to build your own interface. The back jacket uses phrases like “anyone”, “Hands-on” and “low-cost” to describe the book. “Anyone” had better have a pretty good understanding of electronic hardware, not just electricity. The experiments are “hands on”, but most novices would not be able to assemble the preliminary hardware (boards, connectors jumpers, etc.), that “hands on” portion is given sort shrift. The FD-ZX1 boards price is not discussed, but it is ot “free”. Further, some of the parts mentioned are hard to come by (e.g. strain gauges).
Again, the experiments are good and while some important theories are discussed and not implemented, those that are, are done well. Still the distant, slightly too theoretical approach of the authors and need for a commercial I/F board cause me to downrate this work to a 7 out of 10, for the novice reader. Intermediate experimentors will enjoy it more, in my opinion.
©1985 P. Donnelly TSH