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[LoneStar81]

What about 27C010?

As I said, a 1Mbit EPROM (such as 27C010/1001) is 32pin, whereas this 23C1000 one is 28pin. Reading it as 27C010 doesn't work, while reading it as 27C512 works but gives half the data (half of the sounds are missing).

Online it's very hard to find datasheets for 23xxx chips, one thing I could find out though is that they seem to be ROMs delivered from the manufacturer with the desired data already on it. This would mean they need no /PGM or /Vpp pins etc, which could explain why they're 28pin despite being 1Mbit (128k x8 -> 17 address lines + 8 data lines + 1 /CE + 2 power = 28 pins). It wouldn't be hard to make an adapter for the EPROM burner if I had the pinout, which I haven't.
Further, for using a custom chip I'd need to use a 27C1001 or similar, which requires the same adapter again.

So much for the DDD-5 with its 23C1000 ROMs. The R-100's 234001 is out of the question for me, since it's 40pin and my EPROM burner has only a 32pin socket, awww. It would be interesting though if someone with a 40pin burner could read it out. The chip is even socketed for convenient removal.

[Gordonjcp]

Ah, yes, now I remember.  I was starting to decypher this for the TR-505 ROM.  Give me a couple of days, and I'll try and document what I've got.

[LoneStar81]

Good news, I managed to read the DDD-5's ROMs and could fit standard 27C1001 ones with new sounds, thanks to the hints you gave me the other day in the chat, gordon.

The main problem was, the original DDD-5 ROMs are NEC 23C1000 mask ROMS, pre-programmed by the manufacturer. They only have 28pins while your usual 27C1001 EPROMs have 32 pins, so reading the original ones with an EPROM programmer needs a bit of adaption, likewise does inserting 27C1001 ones into the machine.
Apart from that, it works just fine! Next step will be fitting the next bigger type (27C020, 2Mbit), make the highest address line switchable and that way get two soundsets. 95% of the work on this is actually collecting and preparing sounds, the rest is easy going. I'm looking forward to it!