James_S

That's actually fascinating, it makes me realize that I've often viewed more complex and specialized ICs as a black box that does stuff without really thinking about what goes on inside it. I suppose it's the case that these FSMs are integrated into ASICs so they're there, but the end user designing them into something or working on existing equipment doesn't have any visibility into what's happening inside. Now I'm wondering what other devices implemented this sort of discrete design. The vector generator I mentioned is fascinating in that it's essentially a simple coprocessor that reads instructions out of a RAM and then draws the vectors on the monitor without intervention from the 6502 CPU. The CPU loads the object(s) to be drawn into the vector RAM and then the vector generator takes care of the heavy lifting and lets the CPU know when it's finished. This enabled extremely primitive (by modern standards) hardware to generate some really impressive high resolution graphics with glassy smooth framerates. I don't want to take this completely off topic but for anyone interested there is an excellent writeup by one of the original designers here: https://www.jmargolin.com/vgens/vgens.htm

Thanks I'll pass that on and see what happens, as an academic exercise it's worth spending some effort on but it's not worth expending a tremendous effort, your explanation combined with what I already know does make things significantly clearer. Oh yes I realize that FSMs are everywhere, but most of the time these days anything more trivial than a counter or flip flop is typically just done in software with a microcontroller. This particular type of FSM using a ROM that addresses itself through a latch has not come up often but perhaps it was more common back in the 80s. It's also entirely possible that it is a common building block used in ASICs.

I did find the article detailing the construction, unfortunately it doesn't have any specific details about the code in the ROM, only a mention that it was created with the help of a Pascal program which does not appear to have been offered. From what I can see, the source file for the EPROM was never offered directly, the author's company would supply either a programmed ROM, a partial kit with the ROM and PCB, or a complete kit with everything, none of which is any help since the company is long gone and I would not be surprised if the author is dead by now. Yes I'm sure we could work out the "code" to implement a ROM based state machine duplicating the function of the original design given sufficient effort although that could prove to be quite a lot of work and push the effort required to build this one beyond what is reasonably worth doing. I am intrigued by the design though, I have built finite state machines in FPGAs before and but other than in the Atari vector games I can't think of any other places I've encountered one in "real life".

Oh he's aware of other ways to get around SCMS, I found at least one other open source project too. I haven't asked what he actually needs it for but knowing him I suspect it's more a case of the ROM based state machine being an interesting approach to the problem and something fun to play around with. I know he also does a fair bit of repair, refurbisment and other work for a recording studio that specializes in vintage gear so it may be related to that, I can ask if anybody actually cares. We're both engineers with an interest in retro tech as much for the technology itself as for any real need for what it does. While I have no need for it myself, indeed I don't think I even own anything that can record from SPDIF the design piqued my interest when I saw it because it reminds me of the vector generator state machine that Atari used in their vector graphics arcade games from the late 70s-early 80s, those being a long time hobby of mine. Anyway if something turns up great, if not, well as has been pointed out here there are other solutions. It just bugs me because I know there must be a handful of these things kicking around someplace, somebody somewhere must have built one. I've found ROMs for obscure computer equipment from the 1980s so I thought this would be easy.

Apologies if this is not the right place for this. I'm trying to help a friend out with a project, he's trying to build one of the copybit strippers that was published in Elektor about 20 years ago detailed here http://www.minidisc.org/copybit/copybit.html It's a clever design that uses a ROM based state machine built of jellybean parts however he has been unable to find the code for the ROM and my Google-fu has come up dry as well. It was at one point offered as a kit but it seems that company is long gone. Has anyone here actually built one of these? The ROM is a standard 27C512 so dumping the contents is trivial if I could locate a unit to read it from. If anyone does have one of these or better yet has already dumped the firmware from one that would be fantastic.