Title: The Ins & Outs of the
Timex TS/1000 & ZX81
By: Don Thomasson
From: Melbourne House, Dept. CS
347 Reedwood Drive
Nashville, TN 37217
Price: $12.95 (Softcover, 101 pp.)
“At last a hardware reference manual which covers all aspects of the TS 1000!”, reads the Melbourne House ad for “Ins and Outs“. While the book provides a number of interesting tips and schematics, it falls far short of comprehensive coverage. Thomasson‘s book offers clearly printed pages and contains 15 circuit diagrams and 9 other illustrations. Three sections organize the book: Internals, the External Interface, and Externals. In addition, two very short appendices present some simple BASIC and MC driver programs.
Internals supposedly tells us all about the ULA (uncommitted logic array) or “workhorse chip.” However, only 2 pages describe the general function of the chip before Thomasson (figuratively) throws up his hands over the “Machiavellian” complexities of the ZX’s innards. Here he warns us again (the first several warnings come in the third paragraph of the introduction): “very little change is permissible” in the insides of our computers. This theme appears throughout the book: he tells us more about what we can’t do than what we can do.
After a disappointing look at the ULA, Thomasson delves into the TS’s use of IN and OUT ports (FB, FD, FE and FF) for tape loading and keyboard, and briefly describes the video display. He gives simple memory expansion schemes, as well as a basic big keyboard layout.
“The External Interface” pages describe the ZX/TS busses (internal and external) and investigate what those edge connector pins really do. Again we get a very brief view of the various functions available and Thomasson dismisses some out of hand as unusable. For example, for M1 (machine cycle one) he says “no external use can be envisaged”. In fact, many add-on memories need M1 to decode addresses above 32K.
In the last section Thomasson addresses external add-ons: The chapter starts with a basic power supply and then moves to a simple, but somewhat expensive, 16K RAM. But, it appears that some control lines may be missing in the plans. (For instance, one 16K RAM plan shows a WR line, but no RD or MREQ–this memory probably works by itself, but could cause problems when used with other peripherals.) Thomasson discusses basic I/O ports using Z80 PIO and 8255 PPI chips, though again, very briefly.
Next, Thomasson introduces a Centronics style printer interface, potentially the most valuable part of the book. His design (software and hardware) should provide you a solid interface which even supports LLIST, LPRINT and COPY. Like Ener-Z‘s Report Generator board, Thomasson overlays ROM print routines at 0851H with his code. The chapter ends with examples of basic A/D and D/A converters, a sound generator, and 13 pages of BASIC program and explanation of a simulation of a model railroad system, not the real world control system advertised.
This book contains useful tips & hints, and the printer interface concept seems sound. I give this book 6 out of 10, as it doesn’t live up to its claims.
Manual references mean the Sinclair UK manual–with its differences. Display timing (p.13) applies to 50Hz systems. In the British way, you’ll find some obtuse comments, but display and keyboard operations are clear, if brief. Five lines of text hint at how the simulator gets replaced in a control loop–KO.