Have you noticed a distinct change in attitudes about the ZX81? Now, suddenly, from,”wow, I can’t believe how much we can do with so little!”, it’s “ZX81 w/rampack, for sale, cheap.” It seems the time has come–my little computer is, shudder, obsolete. And to think that just a few months ago it was state-of-the-art in “el cheapo” computing. two things bother me though: 1. I bought my ZX to enjoy it, and I still do enjoy it. 2. I bought my ZX to learn from it, and it still has a lot more to teach me. One of the things I have enjoyed learning is that hardware additions and modifications are not just for the experts.
keep it simple with lsi
The first time you wrote a working program, did you have any understanding of just what the computer was doing? Probably not. You really didn’t need the technical informatin to make it work. The computer was simply a “black box” between the keyboard and the TV. When you put the right program and data in one side of the box, out popped the correct answers. OK, so you were no whiz-kid at that point, but you had a functional understanding. That same kind of functional understanding is all you need to use those fancy sound chips, i/o chips, decoders, static rams, etc., etc. Unlike the hardware hackers of yore [yore being about five years ago], we are blessed with cheap, simple, off-the-shelf, single-chip, “black-box” solutions to some very complicated problems. Original solutions to these problems would require a very deep understanding of electronics, and lots of time and money, but a functional understanding of these “black-boxes”, enough to use them, is in range of the novice. Large scale integration makes the job easy.
an adventure in five books
How do you learn to “program” these little black boxes? The first book I recommend is “The TTL Cookbook” by Don Lancaster. It takes a nut and bolt approach, and is not specifically aimed at micro-computing, but it is useful for learning the care and feeding of TTL chips and how basic logic circuits work.
The second book is “Computer Peripherals That You Can Build”, by Dr. Gordon W. Wolfe. The first 50 pages cover digital gates and logic and define the most used computer words. The remainder of the book details how to easily connect your computer to printers, motors, sound chips, plotters, joysticks, household circuitry, etc. If you’re a newcomer to ZX add-ons, this book may get you thinking. The projects are cheap, simple, and easy to build, and almost all include actual schematics instead of the dreaded “block diagram”.
“From Chips To systems” by Rodney Zaks, is a step-by-step tour of today’s micro-computer chips and how they all fit together to produce a wide variety of systems. Zaks is somewhat more theory oriented than the other authors, but he still examines and evaluates individual chips by number and manufacturer. He also gives at least two examples of each type of chip in different applications. The book is very complete, from the history of microprocessors to the future, from 4 bit to 16 bit chips, from traffic signal controllers to personal computers, it covers it all.
The fourth book is really many books. Nothing can substitute for the manufacturers specs to provide our “black-box” understanding. Many provide examples of working circuits, and all are the last word on how to use these chips. Get your hands on some of these books. Any with the 8200 series of chips are fine. These are easy to adapt to your ZX81 and most are cheap. If you want a quick look or photo-copy of a spec-sheet, the Unicorn electronics store has a wide selection and a copier.
Finally, as members of a computer club, we all have one other fine reference book, one that’s hard to beat for specific life-saving advice: the telephone book. If you have an idea or problem concerning your computer and its hardware, call someone. Fellow club members have been more than helpful to me, and I would particularly like to thank Bridgett Kremenec, Jerry Kendrick, and Wes Broszowski.
Maybe, before you give your ZX to your nephew, or sell it for small dollars, you should take off the back cover and experiment a little. There’s a lot of fun and learning lurking in there. OK, it’s “obsolete”, but how many machines won’t be after just a few years?
Gary L Cole