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| Clive Sinclair's ZX Spectrum home computer |
Many years ago I started Microlite by designing an external disk drive interface for the ZX Spectrum. The Spectrum was one of the first home gaming computers in the UK. The firm I was working for had a bunch of Quick-Disk drives gathering dust so hired me to design the interface.
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| Quick-Disk |
The Quick-Disk comprises a 2.8" floppy platter with a single spiral track rather like a record. To access data the drive traverses the whole track (48K-bytes) and this takes 8 seconds. You can turn the disk over to avail of a second 48K-bytes worth. The drive included a read/write head amplifier but no other processing.
The interface hardware was novel in that it used simple logic (TTL gates and registers) and the processing power of the Spectrum's Z80 microprocessor to decode or encode the drive data on the fly.
And then there was the necessary software. It was necessary to reverse engineer the Spectrum's operating system in order to integrate the disk drive and provide the necessary new commands to operate it. All this was done on a 80286 desktop running MSDOS - long before Windows or the internet. My best companion during this period of sheer hard graft was Dickens' Spectrum Advanced User Guide.
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| My best companion |
Thus I wrote a disk operating system or DOS. Others have made millions by so doing - I can't remember what I charged but it certainly did not make me rich, but it did kick-start my business and so I am eternally grateful to Clive, and to John my client, for the opportunity they gave me.
The final Clive Drive was technically a success. A mere 8 seconds to load a game was much better than many minutes with a cassette recorder and the interface supported hacking via the "Keymaster" button. But regrettably the product was not well advertised and was launched towards the end of the Spectrum's lifetime, so I doubt if my client ever recouped his costs.
Surprisingly the world still remembers the Clive Drive - so it wasn't all a dream after all! I found this picture and a couple of links here and here on the internet. The red button is the "Keymaster" button.
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| The Clive Drive interface and disk drive |
For those interested here are some photographs of circuit schematics and operating instructions which, I regret, I no longer have in digital format. Click on a picture to enlarge it.
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| First page of Clive Drive operating instructions |
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| Schematic page 1 |
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| Schematic page 2 - the disk drive connector is at the bottom with RDDT being the raw serial data from the read head, and WRDT the serial data to the write head. |
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| "Peek-Poker" used the Keymaster button to freeze a game and offer various debugging / hacking commands. |
So the links you've included are about some old stock drives and not some recente remake? I was not aware of this drive and I find it rather interesting. Congratulations on your work.
ReplyDeleteNo, not a recent remake. I don't think I have the code any more so could not easily reproduce it, even if I found a supply of quick-disk drives. Do you still use the Spectrum?
ReplyDeleteLovely footnote brought to my attention after googling because of https://twitter.com/yorecomputer/status/1050337304500469765
ReplyDeleteWith some service and a replacement belt drive, a Clive Drive v1.00 works again!!
ReplyDeleteThe two pcbs are very well routed ;-D.
the question...128kb compatible? or only 48kb?
regards.
Only 48K. I did some work later on an adapter to convert a 48K Spectrum to 128K but I have retained no details and cannot remember.
ReplyDeletethe interface do not work of all, i can Format and Save from Basic. When press 1 do not save any file, when press 3 saves a 14K BIN file instead of 7k named Keymaster(n).bin. the ROM version is 1.00.
ReplyDeleteI have observed that in the schemes several mods are referenced. I have compared the components that exist on the board against the schemes you have and there are several values in the resistors that are permuted or the value does not match at all.
When it refers to the ALS type only for IC3 and ic13? or all from IC3 to IC16.
It is also possible that something is not doing well to make a memory dump but the instructions are short for me, the repairs that I had to perform have been: the floppy disk transformer had loose wires, the bus connector It was split and a loose cable that connects both plates. tune the connector of the folded floppy disk drive, and cleaning the printed circuit boards, some resistors are far from the value of the scheme and observing the connector of the disk only 10 signals arrive at the floppy disk, the power is independent of the cable of the floppy disk drive. SELIN (pin15 nc) which should not be important since from the basic could record a short program.
There are too many integrated circuits welded directly to board, where should I start desoldering ?, the SRAM is good is 6116-10, not 150, the EPROM 2764 is read and tested.
If you can provide some additional information that you have will be welcome, this interface must be preserved.
jrmedinam@gmail.com
I have emailed you, Julio. Thanks for your interest.
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