Detective Work Recovers Atari ST ASIC Designs

[Christian Zietz] wanted to know more about the Atari ST. He found information online from newer Atari machines like the Falcon030 and the Jaguar, but couldn’t find much else. While looking through some archives of old disk images from the Atari headquarters, he found a folder marked “Drawings\4118.” With some detective work and emulation of an old operating system, he was able to recover the schematics for the ST-4118 video shifter ASIC (Application-Specific Integrated Circuit).

Unfortunately, this appeared to be a chip for the unreleased Atari Panther video game console. However, it did show the way to how these older schematics were readable. [Christian] continued searching and found some floppy disk images that were a bit unusual. They didn’t have a proper file system but had been created by a backup program called FastBack for MS-DOS.

Simulation with DOSBox wasn’t good enough for the old versions of FastBack, so that was a dead end. However, there was a version for Windows 95 that would work in VirtualPC. The only problem: It expects 3.5-inch floppy media rater than the older 5.25-inch of the original backups.

[Christian] wrote a program to convert the images over and was then able to restore most of the 27-year-old backup archive. Although one floppy image was missing and there was some corruption, he wound up with hundreds of schematics and timing diagrams dating back to 1986 with multiple versions of important Atari chip designs from that era.

He admits he hasn’t found everything. If you are interested in helping, he has the entire set of archives and some additional information linked in his post. We know that poring over three-decade-old schematics isn’t everyone’s cup of tea, but if you enjoy this sort of thing then his work should give you a thrill.

This is a great example of a growing problem. So much data is locked up in formats and media that we are losing the ability to access. Regardless, we do love the old computers. No matter if it is a $4 Z80 build or reviving the Amiga 1200 from photographs, we are into it.

28 thoughts on “Detective Work Recovers Atari ST ASIC Designs

    1. I was just thinking the other day that ‘Digital Archaeologist’ is going to be a profession soon.
      Lara Croft’s grandchildren won’t be Tomb Raiders they’ll be RAID Raiders.

  1. he was lucky. he had disk images. we have a lot of computers in our collection without any media available. they are doorstops at the most right now and the digital equivalent of the dodo

    1. Sure, you may not have original software, but you have the machine. Or do these machines use some esoteric storage medium that isn’t available anymore?
      Write something?

      1. Imagine, 1982 computer that has a big old floppy drive, but you have no boot disks. If you’re lucky, and have another working dinocomputer that can write the correct media, and you know the format, and you have the correct tools on your rescue computer (e.g. hex sector editor) and you have a listing of the source for the content you need to put on that media, and are very patient, you might succeed in recreating a boot disk.

        Weak points being, ability to generate the acceptable sector headers for whatever floppy controller you’re targeting, and having the correct bytes for your disk image. And back in those days, the variety of systems guarantees that there are lots of corner cases out there. Sure, you can probably get images for the more common ones, but those are the systems you can usually find emulators for.

        1. So you bootstrap them the same way the OEM did. Get the floppy controller docs, find or make a memory map, write or reverse engineer the boot rom, make a CP/M CBIOS and bootdisk.

        2. The big old floppy drives (8 inch) could almost universally read the 240kB format developed by IBM, so you would have a chance. 5.25 inch disks had a huge variety of incompatible formats.

    2. The CM Thinking Machines are one of those. I have a friend who’s been looking for the OS for those for years. He also missed out on S/N: 001 of the CM-5 series due to gooberment stupidity.

    1. This is not about the schematics. This is about the internals of the chips that Atari designed specifically for these computers. The schematics have been available for a long time.

    1. “pouring over three-decade-old schematics isn’t everyone’s cup of tea”
      If everyone’s cup of tea were pouring over the three decade old schematics they’d be in a much worse state of repair.

  2. Absolutely love that it’s schematics with gates and FFs (that’s not same as FFS, kids) and “MSI functions”, and not miles of vhdl. You can’t just look at vhdl and understand it, you have to read it, whereas with schematics, it’s just there to see. Not sure why we have to wave our hands around describing e.g. a 3:8 decoder to vhdl, it’s a well-known, well specified chunk of functionality. But trying to compose a system from such elements using vhdl is swimming against the current, so you just do things differently in vhdl. Anyway it’s refreshing to look at simple, straight forward diagrams like these!

    Don’t get me wrong, I’ve built 8 bit CPUs and generated video on FPGAs before, and had a fair bit of fun doing it, and consider vhdl quite useful. Just don’t get me started on verilog =P

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