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A comment on Reverse-engineering the Yamaha DX7 synthesizer's sound chip from die photos. Parent comment

Re:Reverse-engineering the Yamaha DX7 synthesizer's sound ch... by mmastrac on Friday January 12, 2024 @05:55PM (#38975298)
Correct. Those have been available for ages, but there's a mask ROM on the CPU that is undumpable, at least at this time. I have a huge collection of datasheets and I was unable to even figure out what the instruction set was.
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Re:Reverse-engineering the Yamaha DX7 synthesizer's sound ch... by userbinator on Saturday January 13, 2024 @01:36AM (#38977819)
It's likely to be something Japanese, and I know there's been plenty of obscure architectures from them over the years. OKI is known to have made the CPU for Casio, so have you ruled out OKI nX-8?
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Re:Reverse-engineering the Yamaha DX7 synthesizer's sound ch... by mmastrac on Saturday January 13, 2024 @03:31PM (#38984235)
Scanning through my old datasheets I have one from the MSM65512 which probably means I considered that but it's been a while. I should have kept a devlog.

I found an old email to someone that suggests I thought it was an nX/4.

This is a lower-res version of the decapped chip.

https://upload.wikimedia.org/wikipedia/commons/4/44/Oki_m628...

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