My Software

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I wrote some code that when it was loaded from tape, would load a cassette image saved in Sinclair tape format to low memory. This would be a saved image of the Sinclair ROM, although as this was (C) Sinclair Research, I couldn't ship a copy with my emulator. The idea was the customer would buy a tape with my code on it, then save their own copy of the Sinclair ROM, from their own ZX Spectrum, onto the end of it, thus neatly avoiding any licensing issue.

My code would then patch key ZX Spectrum specific portions of it with equivelent MTX code. For example, the code in the Sinclair ROM to read the Spectrum keyboard would be replaced by the code to read the MTX keyboard. I even had code to load and save Sinclair format tapes.

Finally, I stole the top 8KB of memory, and in there I had an interrupt handler, called on a regular basis, which read the area of memory where the screen was on a ZX Spectrum and converted and transferred this into the MTX VDP chip.

The net effect was you could load and run Sinclair Basic programs on a MTX.

However, if you loaded a game written in machine code, and it didn't use a recognised Sinclair ROM entrypoint to access hardware (ie: it did it itself), then this wouldn't work as I couldn't know whereabouts in the game to patch.

Tony Brewer made a product called the "Speculator". This was similar, except rather than load the Sinclair ROM, it would load one of 20 common and popular Sinclair games, and would know where to patch them. It could, for example, run the Spectrum version of Elite, on the MTX.

Finally, for fun, I made a copy of my Sinclair Emulator, which was burned into a set of bootable MTX ROMs. These would be loaded into an MTX ROM card. The first 8KB ROM would be my emulator. The next two 8KB ROMs would be a copy of the 16KB Sinclair ROM. Plug it in and switch on, and your MTX starts up and displays "(C) Sinclair Research" in black text on a white background! In later versions I even cheekily patched the startup message. You appear to have a ZX Spectrum with 44KB, capable of running basic.

This ZX Spectrum Emulator is called "Z", and is included in MEMU, along with a cassette image of the "Gosh Wonderful" improved version of the Sinclair ROM. Yes, you can run Sinclair BASIC, on virtualised MTX (aka MEMU) on a Linux or Windows host.

Military Training

A company in Rome saw SMG and approached me to write some MTX software for a product to be used to help train the Sicilian military! The MTX screen was attached to the sights of a real ground-to-air "turalite" (gun), and it would display a view of a missile flying through the sky, in a parabolic arc. Two soldiers, one controlling the side to side motion of the gun, the other controlling the elevation, would attempt to track the missile, by turning various dials, hopefully at the right relative speeds with respect to each other. My program would receive information regarding the position of the gun from registers on a bit of custom hardware, and would update the screen accordingly. Soldiers would be graded on how much of the time they managed to closely track the missile. As a school boy, I flew to Rome to complete this assignment, and for the week I was there, I had the top floor of a rather nice villa to myself. I became a millionaire as a result, and although it was only a million Lira, that was a lot of money for me at the time.

SDX with CP/M

I got hold of the source used in the FDX for the boot ROM, including the drivers for the keyboard and 80-column card. I replaced these drivers with my own which accessed the MTX keyboard and the MTX VDP chip (in a rather low graphic quality 56 column mode). I also got the source to the SIDISC.COM program, which installed CP/M support for Silicon Discs and RAM discs, and integrated this so it was a part of my new boot ROM. This ROM was known as the SCPM ROM, and has been mentioned above.

The result was a massively smaller and cheaper CP/M system running on a MTX512 with 3.5" SDX disk, and 512KB of RAM disk. I also changed to boot order to try the RAM disk (F:51), if it contained what looked like a valid copy of CP/M. Failing that, it wall fall back to booting from 3.5" disk (B:3). Once CP/M and other files were copied to the RAM disk, this system could boot CP/M in 2 seconds flat, and assemble and link code faster than an SM1.

I had to patch the Newword word processor to make it work properly on a 56 column screen (rather than 80), but once that was done, this platform was perfectly good enough for development work.

Memotech used this boot ROM commercially with their first generation of Video Wall products.

Then I wrote a program RCPMGEN.COM, which would read the RAM disk and create ROM images to burn EPROMs with. These ROMs would be used with a RSCPM boot ROM, which at boot time would copy the RAM disk images from ROM to RAM disk. The net effect was you could make a MTX512 with MTX ROM card and MTX RAM card and no floppy disk, which booted CP/M from ROM. This made use of a "sub-page" feature in later ROM cards whereby one of a number of 8KB pages could appear in a single ROM page slot, selected by writing to location 0 in memory.

Video Walls

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After Memotech gave up selling home computers, it started designing, manufacturing and selling video walls.

I wrote the software to control these, which ran on CP/M on the SDX with my modified boot ROM. The video walls were controlled by sending command strings down the centronics printer ports. This allowed Memotech to use its stock of MTX kit as a part of its video wall offerings. I subsequently wrote better software which ran on MS/DOS on the IBM PC.

I still have the source to both the original MTX version and the later PC version of this. I even recently modified the PC version to work on modern PC hardware, which is massively faster than it was at the time.