Z80 Instant Programs   J. Hopton   Sigma Technical Press.

This paperback volume of 180 pages is published by the Sigma Technical Press and costs 7.50. Sigma Technical Press, it seems, is no relation to Sigma Accounting, the authors of ZEAP, the Nascom Z80 assembler. The book sets out to describe a number of Z80 based machine code programs, many with little or no system monitor dependence. The summary says that there are 36 programs listed, but having read the volume I imagined there were more. The Programs cover most aspects of machine code programming relevant to the home user, ranging from simple delay loops, through simple arithmetic, to simple text handling routines.

The book is primarily based on a Nascom 1 fitted with a Nasbug T2 monitor, and an appendix of the main monitor routines is given, the implication being, that users of other Z80 based systems adapt the programs given in the book to their system. Unfortunately, for instance, the location of the screen memory (0800H – BFFH) is implicit within the monitor routine, and therefore unlikely to be of help to anyone not owning a Nascom fitted with Nasbug 172. Likewise, the keyboard routine given is the routine for the Nascom software scanned keyboard, and as Nascom is the only company using this particular keyboard, it is not likely to be of much use to other Z80 system users. These routines were however beautifully commented, in a particularly easy to follow fashion, so whilst not much use to anyone other than a Nascom owner, they provide a useful insight into the workings of these monitor routines.

It is difficult to tell who the book is aimed at, as it certainly is not at ‘beginner’ level, there being nothing but the sketchiest explanation of what the various registers are supposed to do or how the Z80 works. No explanation is given regarding memory mapping or how a certain area of the Nascom memory is set aside for the screen, etc. There was a very simplified explanation of what an op-code is, but the word ‘operand’ did not seem to figure at all. To the more experienced programmer, a lot of the detail in the explanations would be dismissed as trivia. Although the programs were adequately explained I feel the beginner would be left with the feeling that the machine code instructions themselves were even more like black magic than when he started.

Some interesting hardware examples were given, driving LEDs from the ports, D – A and A – D converters, attaching a speaker to play a music program, etc. Although these were not tried, there is every reason to believe that they would work.

Many of the programs are long, and as an aid to correct loading, a tape is available from the publishers. The tape is in Nascom 1 tape format and is unsuitable for Nascom 2. Be warned, the first few minutes of the tape are a spoken commentary, and of course, will not load into the Nascom. Although I did not have the tape for the review, those programs I typed in and tried worked.