Ah, Visicom, so I can't blame fauxscot.
Well, as he frequently comes to me for help ID'ing chips, Guru's challenge to me in 2008 was:
On Sat, 28 Jun 2008 11:06:02 +0800, "Guru" said:
> I need info / datasheet on a chip
> Toshiba TMM331AP
> It's some sort of ROM, from that old Toshiba console that arrived
> Did a quick search and nothing came up except part sellers. I'm sure
> you'll have more luck :-)
So he and I spitballed stuff back and forth about what it could be. He credits Dox, I don't remember him being involved but perhaps it was in another email conversation. But yeah, I eventually found some Japanese whitepaper on some science project or military hardware, using various derivatives of the chip name and Google techniques, and Yasu translated it (I don't remember Gridle's involvement?) which got us thinking about possibilities of what the ROM chip could be, and its capacity. I could find datasheets for nearly every other Toshiba TMM3xx chip, but not this one. Still, Guru worked out like 80% of the pinouts and did a test dump which looked okay to people armed with disassemblers. That was around December '08-January '09.
Also immediately following then in December 2008 I found a snippet view in Google Books of some large electronics catalog that claimed the ROM chip was pin-compatible with AMI S6831. And then we acquired that datasheet, and it matched the pinouts, but not the capacity (and voltage? something like that...)
I wouldn't let it go though - I was sure the actual Toshiba datasheet must exist in a databook that was as-of-yet unscanned. So I would occasionally worry that little search project until I found more information, pestering certain databook scanners to upload more Toshiba memory books of the era... I even ended up forgetting the snippet view/chip compatibility discovery and rediscovering it again a few times over the last few years.
Anyhow, like any of Guru's attempts at dumping completely unknown/unremembered ROM chips, it was based on whiffs of clues of what it could be, tracing out circuitry on old circuitboards, and lots of educated guesses based on other chips with similar part numbers and his years of experience.
Anyhow, that's how I remember it based on old emails. Perhaps Dox and Gridle were involved secretly, I can't remember.
But a MAJOR pain in the ass because whatever databook the TMM331 is hiding in has not yet been scanned to PDF. Assuming it wasn't custom. But it doesn't seem to be, just undocumented and uncommon. If we'd had the actual datasheet, that would have saved months.
On the other hand, actually creating a dumping rig that can be used repeatedly and that isn't educated guesses and much more reliably based on Electronics Engineering? That's alllll Charles.