I offer two unequivocal statements for the record:
1: Yes, ZX81 user support has moved “underground”.
2: NO, the ZX81 support market is NOT dead!
Because of fact#1 (despite fact#2 ? ), I am constantly encountering fellow computerists who simply don’t know where to turn for information about support for their computer. The state of the ZX81 market is such that user participation, communication, and mutual support are absolutely crucial. When Timex pulled the plug, so did many of the larger aftermarket support companies. What did that leave? The truly dedicated supporters and enthusiasts who saw the potential of the machine, rather than just the dollar signs in an “up” market.
Fact is, folks (newcomers and old hackers alike): the free rides are (long since) over. It’s up to US to support suppliers with our business if we expect them to continue. It’s up to US to communicate with each other- to share information and ideas. I speak from both sides of the fence here: Timex’s exit has rendered us equal, supplier and user alike, in mutual support requirements.
Many newcomers to ZX land have expressed concern that there isn’t much ZX81 support available these days. NOT SO! A lot of the extraneous garbage (which certainly padded out the appearance of the marketplace) has disappeared, but what’s left is the cream of the crop. Name virtually any conceivable software application, hardware upgrade, or communications support that was ever available during the “Timex peak”: all the best is still available, and will continue to be for a while. My list is still growing, not shrinking!
Now arise the questions:
-“How do I find out who this stuff is available from?”
-“Where and how can I learn more about my computer, and share what I’ve discovered with others?”
Fortunately, there are several answers. Participate in the activities of your local User Group. Get to know the skills & interests of other members- and make yours known, too. There’s ALWAYS someone who can benefit from knowledge you may take for granted. Similarly, those who don’t ask don’t get. DO NOT be embarrassed to ask questions of more experienced users. We all must start somewhere. I’ve never met an unfriendly ZX user!
There is no rule that says you can only belong to one User Group. Currently, in addition to at least 5 dedicated “real magazines”, there is a large (and growing) number of active User Groups across the continent, many of which publish excellent Newsletters. By subscribing to a few of these publications, you will find yourself overwhelmed at the resources available to you. Your interaction with support publications should NOT stop with your subscription check! The articles & letters you read were contributed by someone just like you. So if you have a program you’ve written, news you’d like to share, praise, or a gripe, then write about it and send it in! Most newsletters also offer free classified ads to subscribers as an additional benefit.
** BUG ALERT ** BUG ALERT **
Owners of AERCO CP-ZX Vers. 2.2 Centronics interfaces please take note. The AERCO CP2.2 ROM has, in addition to an ASCII printer driver, a Disk Boot routine patched into the machines’ initialization. On power-up, it checks for an AERCO Disk interface, and if there is one, it proceeds to load the Directory page from Drive A. If there’s no Disk system, the initialization continues, and up comes 0/0 (!). This is because during the Disk? check, the CP2.2 actually forces the machine to execute a BASIC line embedded in the EPROM code. Thus, the machine comes up with a 0/0 instead of a K cursor.
To the point: in the midst of this exotic initialization scheme, the CP2.2 somehow sets up addresses 16507 and 16508 to hold a critical status flag for the operating system. To the normal ZX/TS ROM, these two bytes are completely unused and ignored. They frequently get used as a “cache-all” register by many Machine Code programs (e.g. HOT-Z, ZXLR8, & many “toolkits”). The problem is, with the CP 2.2 interface attached, ANY PROGRAM which loads in from tape with values other than 0 in 16507/16508 will crash if you try to BREAK it. Even if a program loads in with these bytes OK, if it changes their value at any time, you are probably out of luck.
Some programs which exhibit this problem can be “cured” by loading the program without the interface attached; Break, then POKE 16507 and 16508 with 0, and re-SAVE the poked version to tape. The new version should now LOAD (and Break) OK with the interface attached.
AERCO now have available an improved version of their CP-ZX ROM, Vers. 2.3, which they claim has the problem eliminated. If you have a 2.2 or earlier version of the AERCO ZX CPI, you should enquire about getting an updated version (either free or for a very nominal price) from AERCO, 7606 Robalo Rd., Austin, TX 78757.
** HARDWARE USER REPORT **
SUBJECT: The JLO Video Upgrade Project, available from
The John L. Oliger Co.,
11601 Whidbey Dr., Cumberland, IN 46229
INTRODUCTION: Since Mr. Oliger manages to keep quite busy without doing any real advertising, a lot of folks are unaware of the fine products he has available for the ZX81. A certain mystique has built up around JLO products, which I hope to dispel. Yes Virginia, John Oliger is a real person, who answers mail, ships orders on a realistic schedule, and has some pretty neat ideas.
Just what sort of peripheral is this Video Project? Let me begin with a sweeping analogy: the Video Upgrade Project is just like a video monitor, a disk interface, or a fullsize printer. Once you hook up a monitor and get used to it, the ol’ TV set just won’t do anymore. When you get a disk drive, you madly transfer all your software, and then avoid cassettes like the plague. When you get a real printer, the 2040 generally becomes a hi-tech paperweight.
Likewise, after having the Video Project (VP from here on) for a couple months, I loathe going back to the flashing, flickering snail’s pace of “normal” video which I have lived with for so long.
WHAT IS IT? Remember the ill-fated Kolorworks board, and the ColorSin81? Both were color video boards for the ZX81, which never really hatched due to various impracticalities. The JLO VP surpasses both. It is elegantly simple, thus economical. The firmware integration to BASIC reflects the same qualities, and is virtually transparent to 99% of existing software.
The VP consists of 2 circuit boards which plug into the back of your computer. These boards have a male edge connection only, and are meant to plug into a motherboard. Compatible motherboards are available from JLO, or from Maplin or Eprom Services in the UK.
Video Board “A” holds a Texas Instruments TMS9918A Video Display Processor, 16K of dedicated Video RAM, and 1 decoder chip. This video RAM does not occupy any of the Z80’s address space- the Z80 communicates with the VDP & video RAM through I/O ports 3F & 7F.
Video Board “B” has sockets for two 2764 (8K) EPROMS, and 4 decoder chips. Eprom “A” is mapped to the 0-8K area, and overrides the internal ROM in your computer. It is identical to the ZX BASIC ROM, except for the parts which deal with generating a video diplay. All the real work is now done by the VDP. The Z80 just sends it the necessary data and is free from the actual task of generating video.
WHAT DOES IT DO? Two advantages which are immediately apparent are speed, and continuous display. In SLOW mode, the computer is now almost as fast as in FAST mode. In fact, it can be difficult to tell which mode you’re in at times. In FAST mode, the display doesn’t go blank. It just remains static until you come to a PAUSE, INPUT, or SLOW command. There is absolutely no screen “jump”, flashing, or flickering, at all, in either SLOW or FAST mode. Entering and editing BASIC programs is a real pleasure, especially in FAST mode. The old screen reformatting games of the ZX81 are gone! When you Enter a line, it simply (zap) appears in the listing. LOAD and SAVE are rather interesting. When you enter a LOAD or SAVE command in FAST mode, the command stays on the screen through the tape operation. SAVE and LOAD activity is shown by the border rapidly flashing through a sequence of 16 colors! The effect is similar to that of the 2068 LOAD & SAVE patterns.
How about software compatibility, kit building details, and the bottom line?
SOFTWARE COMPATIBILITY: As mentioned, the JLO VP is compatible with just about all software. The main exceptions are fast machine code arcade games, like Frogger, Pac Rabbit, etc. They run, but so fast they’re generally impossible to play. By the same token, some games that were boringly slow before are now a real challenge. Psion Flight Simulator now responds like a jet fighter rather than a Cessna. Mazogs is simply a hoot. BASIC programs with lots of calculations or plotting really benefit, too. The only software I have found that’s truly incompatible with the VP uses software-only means to simulate hi-res with the standard machine, or tries to peek the character generator of the ROM to get pattern data. This includes games like Forty Niner, Sea Mines, and ZXtricator, and utilities like N. Elmaleh’s SW HI RES and Callisto‘s Graphica. You simply have to unplug the video boards and use standard video for these programs.
CAVEATS, THE BOTTOM LINE, ETC.: The Video Project, as the name implies, is available only in kit form. You may purchase either just the bare circuit boards with instructions, or get an (almost) complete kit of parts. For $48.95 U.S., you can get both boards and all parts except for the actual VDP chip and its crystal. The TMS9918A VDP chip is available from several parts suppliers at widely varying prices. The best I’ve seen is $9.95 from Jameco Electronics, in Montreal. The 10.7386MHz. crystal is also generally available for about $5.00. When you order a VP kit, JLO will include a listing of the current best sources for the VDP & crystal. By the time you account for all the tidbits, allowing for a motherboard if you don’t already have one, etc., this whole thing is roughly a $100.00 proposition.
The kit instructions are complete and reasonably clear, but I really can’t recommend this as a first-time project for the prospective kit builder. You must be able to do very fine soldering on these circuit boards, and some familiarity with good electronic assembly & soldering practices is truly an asset. My only complaint is that, for economy’s sake, the feedthrough holes on the double-sided circuit boards are not plated through. This means you must solder in a healthy number of tiny wire feedthrough conductors before mounting any parts on the circuit boards. Believe me, this is a tedious and time consuming task, after which soldering the actual parts in place is a breeze.
A minor modification must be done inside your computer to permit functioning of the VP. The NMI line between the ULA and the CPU must be cut, and a diode and resistor added. This is very simple to do, and does not affect the normal operation of the computer. This mod is much easier to do on the older Issue 1 ZX81 boards than on the later Issue 3 layout.
Last but not least, you must supply and program your own 2764 EPROM for the modified operating system. Mr. Oliger will supply a tape for his 2764 programmer, which contains the necessary code and will automatically program your new EPROM. Most of the code is gotten from your resident ROM, so if you have, for example, Tom Bent‘s 8K ROM UPGRADE, all the improvements in it will also appear in your new video ROM.
John Oliger has kindly put his operating code in the public domain. If you don’t have an Eprom programmer, don’t despair. Tom Bent will supply the VP EPROM with his Vers.10 ROM improvements as well, for $25.00. I can supply a VP EPROM based on the TS1000 ROM for $10.00, to cover cost of the EPROM and postage. In either case, you must specify whether you want 16K or 64K RAMTOP initialization, default paper, ink, and border colors, etc. That’s the lazy way out, though. An EPROM programmer is a really handy gadget to have around, and represents a modest investment. JLO’s programmer is a snap to assemble- it uses plated through holes. Building up a motherboard & EPROM programmer is good practice- it’ll sharpen up your soldering skills (and confidence) before tackling the Video Project. And you’ll learn a lot more.
ADVANCED FEATURES: So far, we’ve discussed only how compatible the VP is with existing software. By executing certain RAND USR commands, you can choose between normal ZX characters, or lower case instead of inverse on the screen. The old system variable MARGIN is now the COLOR system variable: you can poke different values to this address to select INK and PAPER from 16 different colors. That’s the limit of the extra commands available from BASIC, but by using machine code to communicate with the VDP, it is capable of 32, 40, or 64 column screens, true hi-res color graphics which are in some respects superior to 2068 graphics capabilities, and real sprites, definable on 32 different planes! In addition to this, the VP removes virtually all the funny display-dependent limitations of the machine. Minor modifications will permit machine code to run anywhere in 64K, and even Mode 2 interrupts can be used. For machine code programmers, the IX register is now available for use, and the R register is used in the normal Z80 fashion. No limitations exist on the location of DFILE in RAM, and “illegal” characters (i.e. tokens) can even be poked into the DFILE without causing a crash. Since the character patterns are stored in video RAM rather than in ROM, it is possible to have programs load in with user-defined character sets- excellent for games and wordprocessors. I’m now running Word Sinc II.5 with upper and lower case onscreen, as well as special symbols for control characters. Prospective software support is exciting, too: Silicon Mountain Software now have a tape version of Memotext with a 64 col. onscreen viewing option, as well as a 64-col. hi res color extended BASIC for release in the not too distant future. And Callisto Software will be producing an exotic graphics toolkit for use with BASIC, as well as a hi-res screen, color version of Sinc-Artist!
IN CONCLUSION: The JLO Video Upgrade Project is an extremely well conceived and executed product. For the ZX81/TS1000 hobbyist, this is an excellent opportunity. It gives you speed and video capabilities at least equal to the 2068 (the video is actually MUCH more stable), and improves the performance of most existing software. You get SUPPORT, too. If you can’t get your kit to work, you can send it back to JLO along with $15.00, and he will locate & fix the problem for you.
FEATURED NEXT ISSUE: THE AERCO FD-ZX FLOPPY DISK