Heathkit’s entry into the world of small systems could represent a breakthrough in affordable computing.
By Ron Harris
The Zenith Z89 is a dual processor system based upon the Z80 CPU chip. In effect it is two machines in one box. The VDU has its own controller, totally independent of the main CPU. Standard memory configuration is 48K of user RAM with 8K of system RAM and ROM. The keyboard is a fairly standard QWERTY affair, with a 12 key numeric pad also adorning the front panel. The VDU has… look – hold it here a minute. This machine has more facilities than I’ve had hot dinners and if I go on listing and describing we’re all gonna be here until the sun goes cold and England win the World Cup again.
Table One is a summary of the hardware features of the system and after you’ve glanced down it I’ll go over some of the more interesting abilities possessed by the unit.
Any Port In A…?
Expansion possibilities revealed
There now. That didn’t take long. One thing not mentioned are the output ports to allow for the hanging on of peripherals. These are RS232 standard with a data rate of between 110 and 9600 bps, user specified. Parity can be odd, even, or anything else you can dream up, it is flexible.
The system as a whole is exactly that – flexible. The machine makes use of its size to offer the user a flexibility and potential undreamed of – and undreamable – in the lower priced computer systems.
At this price, which could be described, at present, as lying above the high priced home machines, the Sorcerors and the rest and yet below the lowest end of committed business systems, who can be expected to seek out and purloin a Z89? Well, anyone needing a very versatile and powerful computing tool, with an excellent built-in disc facility and great ‘keyboard’ power would be advised to look here. The Z89 can be an absolute top-class home system, or a very useful business machine for the smaller company, take your pick.
Fig. 1. And this is just a system diagram!
It seems to fulfil what many of the earlier machines promised – but fell short of. It is truly a complete, yet expandable, computing system. It arrives with built-in disc drive and facility for adding on an external Z87 dual disc. Each ‘diskette’ has 100K of storage and is of ‘hard sector’ type, which means that the size of each sector is hardware determined by the PCB, not by the software controller. This in-turn means that the sector size is fixed. Sectors are allocated to files in ‘increments’ of two ‘256-bytes’ as required by the operating system.
What Comes With…
Heathkit supplied us with all the manuals you ever dreamed of, including the one for the WH 89 – the kit version of the Z89. Mind you, kit is a misnomer really, as most of the PCBs arrive assembled! Module assembly would be a better term. As usual for Heathkit, the documentation is faultless, if a little daunting in this case. We got a huge binder for CPM, one for HDOS, another two for BASIC and a three inch thick WH 89 manual with circuit diagrams. The latter are complete down to component level, with full overlay documentation.
Well, I’ll believe they’ve thought of everything – lest ten more manuals drop through my desk. You know, with all this paperwork – most of which contains a “What to do first” section, couldn’t they add just one more little bit? A small, totally separate, approachable little pamphlet for each configuration, telling you how to get it up and DOING something, as opposed to sitting there humming gently and looking smart. On behalf of all the people who will buy this machine, take it home, put the plug on, switch on get “H:” on the screen – and get that empty “Oh God what now?” feeling in the pit of the stomach, PLEASE Heathkit?
Still, back-up looks like being very good and I doubt if even the most obnoxious purchaser would find himself turfed out in the street, box in one hand and manuals in the other.
Heathkit were very helpful indeed to us – even putting HDOS onto each of the discs they loaned us to save messing about having to keep shuffling the source discs.
The hard sectored disc can be back up by two external brothers.
All neatly packed in with acres of room to service.
After experimenting with both the CPM and HDOS we were provided with, I developed a preference for HDOS to the extent that CPM stayed in its folder after the first couple of runs, unbidden while HDOS spun its triumphant way across the heads.
Somehow HDOS is simply more usable and flexible – it lets you get at the material it is handling with the minimum of interference and the maximum facility. The perfect librarian, in fact – and what else can you ask from a disc operating system?
The folder for HDOS is very well written and produced and the opening chapters nicely sectioned with “First time through” lists every now and then to help a new convert learn his art. That little pamphlet I wanted could be no more than these sections extracted and re-presented. As it is, if you don’t know where to look you’ll never find it!
My advice to any new or aspiring owner of a Z89 is to sit down, with a cup of tea and the HDOS manual and READ IT. It is approachable and conversational in style and easy to digest, managing to avoid the usual half incomprehensible flood of abbreviations and jargon that swamps some rival efforts. A new user needs to be told what he has obtained for his money, not shown what a clever little boy the manual author can be. Heathkit could hold classes for the opposition on producing manuals – if any of them would bother to go, that is.
Fig. 2. Schematic of the elephant’s brain!
Side One, Track One
Supplied with the Z89 is a ‘distribution diskette’ as they call it, containing the operating system, HDOS, with a few very useful little ditties, like BASIC, DBUG, EDIT and ASM. I’m afraid that in the space I have in this magazine I can do little but whet your appetite as to the scope of these files. Suffice it to say:
- BASIC an extended 16K BASIC with all that implies. This is the ‘Benton Harbour BASIC’. Microsoft BASIC 80 is also available, but requires 28K of RAM, and thus will run best on the minimum of a 32K system. No problem with a Z89. This includes line renumbering, amongst other things, and sufficient facilities to make any BASIC nut offer up an arm or two.
- DBUG makes use of HDOS to allow for full debugging of machine-code programs. Will display and alter the contents of any specified memory location, or 8080 compatible register; will execute a program either completely, or line by line; will load or dump programs onto discs, printers VDUs etc; and will insert ‘breakpoints’ executing several instructions then halting with control returned to DBUG.
- EDIT the Heath Text Editor. Will do nicely as a word processor, providing good editing facilities with 15 editing commands. You could write the annual report on this – or a note home to granny asking how the budgie is doing. Works very well too for editing BASIC programs.
- ASM Heath Assembly Language Program. Once you’ve got used to the EDIT you can use ASM to run source programs on the Z89. For best use you will have to know the 8080 pretty well.
As I said before there is much much more to these titles than I could get into a single issue. All I can do is recommend the supplied software very highly. It is well thought out and nicely tailored to the system. Useful and useable.
One of the two main circuit boards with its daughters
With the hardware configured as two interactive portions we have a potentially very powerful beast and a potentially confusing one. The key to the whole operation is a little key tucked at the top left of the keyboard. Called OFF LINE, it means exactly that. Press this down and you disconnect the computer from the keyboard and screen (Fig. 3). This means of course that you can go on typing until your fingers drop off but the computer is totally ignoring you.
Fig. 3. A Trap for the unwary
The advantages are great. The cursor can be shifted around, lines cleared – even screens cleared – without code transmission and hence the program knowing about it. Of course if you forget to put it back on-line………………………
There are eight user definable keys strung along the top of the board, which you yourself can set up to be something worth using – instructions are of course provided to do this.
Having an intelligent keyboard takes some getting used to after more basic systems, but it is a luxury you soon learn to live with, I promise you!
It might be illuminating to go through how you get the Z89 to run a program from scratch. Let’s choose BASIC as an example, assuming that your distribution disc supplied with the machine contains Microsoft BASIC (MBASIC).
At switch-on “H:” appears in the top left of the screen and nothing else. You place your disc into the drive – getting it the RIGHT way around and type “B”. The screen turns this into “BOOT” and a RETURN will bring you a “TYPE SPACES TO DETERMINE BAUD RATE”. You now have to hit the space bar repeatedly for a few sections so that the system can pick up the speed at which your terminal operates. Then “ACTION? < BOOT >” appears and a RETURN gets you “DATE [DD-MMMYY] ?” This is simply so the system can preface all your files with the origination date. Type it in and RETURN. A “ > ” now appears and you have loaded HDOS.
HDOS contains a test and a diagnostic routine, but we’re after BASIC, so all we have to do now is type in the file name, MBASIC and wait until the clicking and flashing from the drive ceases. The screen will display the header for Microsoft BASIC, telling you which issue it is and how much RAM you’ve got left to play with. If you’re a small systems man, being told that 21K remains free will probably induce feelings of inadequacy. Fear not. It is all under your control………(isn’t it?)
Impossible to do. Summarising a machine only slightly less complex than the Secret Of Life is too much for me to cope with. My own impression of the Z89 is that it is a well designed, flexible, well supported computer that knocks the opposition sideways. It would be equally at home on a dining-room table or an office desk and should be examined very carefully if you have this amount to spend on a system. It is worth the extra for its flexibility and power.
I wonder if Heathkit would accept a slightly used soul as down payment…………..?
|Table 1. All these features add up to an awful lot of power and flexibility.|
|Memory||48K bytes RAM. 8K for systems ROM and RAM. 8K reserved.|
|CRT||12” diagonal, P4 phosphor|
|Display Format||24 lines of 80 characters, plus 25th user status line.|
|Display Size||6.5” high x 8.5” wide|
|Character Size||0.2” high x 0.1” wide (approximate)|
|Character Set||128 (95 ANSII, plus 33 graphics)|
|Character Type||5 x 7 dot matrix (Upper case); 5 x 9 dot matrix (lower case with descenders)|
|Keyboard||72 keys (60 alpha-numeric, 12 function control) plus a 12-key numeric pad|
|Cursor||Blinking or reverse video block or off|
|Cursor Controls||Up, Down, Left, Right, Home, CR, LF, Back Space and Tab, from keyboard or computer|
|Cursor Addressing||Relative and direct|
|Tab||Standard 8-column tab|
|Refresh Rate||60Hz at 60Hz, 50Hz at 50Hz line frequency|
|Edit Functions||Insert and delete character or line|
|Erase Functions||Erase line, from beginning of line to end of line, erase page from beginning of page to end of page|
|Bell||Audible alarm on receipt of ASCII BEL|
|Video||Normal and reverse character|
First published in Computing Today, June 1980