Reverse-engineering the Yamaha DX7 synthesizer's sound chip from die photos

Re:Reverse-engineering the Yamaha DX7 synthesizer's sound ch... by mmastrac on Friday January 12, 2024 @03:57PM (#38973942)

Ken, if you have some spare bandwidth I have some high-res decap photos from the chip in the Casio SK-1!

I worked on trying to reverse engineer the instruction set from that chip, but most of the code is in a mask ROM that probably needs some debug wires to extract.

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Re:Reverse-engineering the Yamaha DX7 synthesizer's sound ch... by nobleach on Friday January 12, 2024 @05:19PM (#38974898)

The demo song from that thing will forever live rent-free in my head. Sometimes I sing it to myself, and then pretend I've switched the lead instrument to a sample. (hi, hi hi hi, hi hi hi, hi hi hi hi hi....)

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Re:Reverse-engineering the Yamaha DX7 synthesizer's sound ch... by ajxs on Friday January 12, 2024 @05:28PM (#38975013)

There's a zip file here with the Casio SK-1 ROM: https://dbwbp.com/index.php/9-misc/37-synth-eprom-dumps

Maybe this could help. Is there some mask ROM on the CPU that isn't included here?

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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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Re:Reverse-engineering the Yamaha DX7 synthesizer's sound ch... by kens on Friday January 12, 2024 @07:02PM (#38975854)

Thanks. Much as I'd like to reverse-engineer the Casio SK-1 chip, I'm trying to stay focused on my current projects.

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Re:Reverse-engineering the Yamaha DX7 synthesizer's sound ch... by johndmcmaster on Saturday January 13, 2024 @03:40AM (#38978227)

Consider asking in the sipr0n discord decap-commission channel: https://discord.gg/qyne7GZk

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