Reading Sinclair Interface 2 Roms

Philip Mulrane 25/6/2000 

This document details my efforts to read Sinclair Interface 2 Roms, in order to run them under some of the Spectrum emulators.



Sinclair's interface 2 for the ZX Spectrum is a bit of an odd wee puppy, comprising, as it does of a twin joystick interface, using its own standard instead of the then dominant Kempston standard, a pass-through of the expansion bus which is pruned, allowing only a ZX Printer to be attached, and most importantly (for the purposes of this document), a rom slot for cartridges.
There were ten such cartridges released by Sinclair:

They were intended to compete with the games consoles of the day, but were not very successful.

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The slot

I used a multimeter to find out which connecting pin of the slot corresponded to which bus signal. Here are the results:

The only point of interest here is that all 16 address lines are present, and the address decoding seems to be performed by additional logic contained within the cartridges themselves. Maybe it was planned to construct cartridges which would be able to map out the upper 32K of ram in order to allow cartridges larger than 16K? My electronic knowledge fails me at this point, maybe someone else out there could enlighten us on this one.
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Reading the roms

In order to read the cartridge roms, I constructed an adapter allowing me to plug the cartridges into my BBC micro eprom programmer:

I then copied the rom images to my PC via an Archimedes. Hex dumping through the roms reveals that most of them are only half full! And the ones that are full are padded out by a 'loading screen' 6912 bytes long. I have images for nine of the roms:

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Use with emulators

To use a given rom with a given emulator, you need to replace the 48K basic rom with the rom of your choice. Some emulators have an option for this, for other's you need to rename the existing 48K basic rom so that the emulator can't find it, and then copy the cartridge rom to a file with the same name as the original 48K rom.
I've tried the rom images with several emulators:

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As you can see from the above list, I'm missing one of the original cartridges: Pssst. It would be great if someone out there would be prepared to swap/loan the missing cartridge, so that I can read it's contents, and make them available to the great Specyfying public.
I have about 7 of the carts as doubles, so I might be prepared to do a two for one swap.
If you are interested please email me at: [email protected]

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