Publisher: Melbourne House
Price: £9.95 (paperback)

If you are still enamoured with the Spectrum Z-80 processor you may have noticed the lack of good reference material about the instruction set.

There are few books which catalogue the instruction set, show the timings of each command, with examples of usage. The Z-80 Reference Guide comes as a pleasant surprise.

It starts with an introduction to the register sets and a general explanation of timings for each type of instruction. A page is devoted to each instruction giving a general description of usage, the number of bytes used by each, the flags affected by execution.

The book bears a striking resemblance to The Z-80 Programmers' Reference Guide, by Rodney Zaks. That includes a comprehensive course on Z-80 programming, something which Tully's book omits apart from a puny chapter giving hints and tips.

Tully's book will never beat Zaks'. It is, however, useful for beginners who want a quick reference to a particular instruction.

The last two books are machine code based and directed at the experienced programmer or perhaps very enthusiastic beginner. Both are published by Melbourne House, the former costing £8.95 and the latter £9.95.

Spectrum Shadow Rom Disassembly, by Gianluca Carri, is written in two parts. The first shows how to extend Sinclair BASIC to include various useful commands, random file handling on the microdrive, extended BEEP and EDIT commands. Full details of the implementation are given along with very clear explanations.

It is possible to add extra commands to the Spectrum with an Interface 1 unit, containing the Shadow ROM, because when an invalid command is found, a search is made in the existing Spectrum ROM. If this command is not present, then the Shadow ROM is searched. If the command is not found again, then it is at this point that we can jump to our own routine, and carry out the extra commands.

There are two types of Shadow ROMs, and this book accommodates both. There might even be another release of the Shadow ROM software, but the author still explains fully what to do if this is the case.

The second part of the book gives a full disassembly of the Shadow ROM in the Interface 1, and how to link up and use these various routines. This is ideal literature for the Z80 programmer wishing to either add commands to BASIC, access the microdrives via machine code or see what's in the Shadow ROM.

The second new book from Melbourne House is the Z80 Reference Guide by Alan Tully, which is intended as a reference manual for the Z80 programmer.

The book is designed to help the Z80 programmer, who perhaps is stuck with a programming problem, to choose the correct Z80 commands to use. An excellent chapter is included which lists the Z80 instruction set and where best to use the various commands. The bulk of the book is a summary of the Z80 instruction set, which gives full details of each individual instruction, along with the effect on the flag register and the timing of the specific instruction. Excellent examples of usage are also given for all but the most simple instructions.

The book covers a vast topic and is ideal for anyone interested in machine code, either to be used by itself or as a supplement to an existing 'Learn How To Program' guide. Although this book is expensive at £9.95, it is well worth having an empty pocket for all those who are into machine code (better still, you could rush out and enter our competition for copies of this book, elsewhere in this issue - Ed).

By Alan Tully
Melbourne House
£9.95

Learning and then understanding machine language is not so very different from learning any other language - English, for instance. The only difference being that English is far more tricky - but you learnt that OK, so why all the fuss about learning another one?

When you set out to learn a language the first two things you'll need are a tutorial and a dictionary. This book is quite simply a Z80 dictionary. Inside you'll find a detailed description of each instruction just as a dictionary defines words. There are tabulated lists of them all with their timings and the effect they have on each flag. A whole page and sometimes more is dedicated to each so they can be covered in full, including a table of their object codes in both Dec and Hex.

More than this, though, the same instructions occur in other parts of the book in different formats according to the different but relevant types of information that surround them. Perhaps a closer analogy is of a dictionary combined with a thesaurus as well.

Moving through the book, you'll first come across a chapter on the three types of Z80 registers - general, specific purpose and the flag register. Most room is devoted to the flag register for the simple reason that it's the most important of them. There's also a useful table showing which instruction affects which flag.

Now, very few books highlight the importance of timing in machine language and how crucial this is to games programming. Well, this one does! So. If you've no idea what a T or an M cycle is, or more to the point, if you've forgotten, then you can look it up here.

But be warned, this book is not bedtime reading - unless you're in the habit of taking your dictionary to bed with you. As its title tells you, it's a reference work and as such it won't even teach you machine language ̶for that you will need a tutorial. What it will provide is a solid back-up to your language learning and it'll prove a handy memory jogger for even the most hardened machine code programmer.