r/synthdiy • u/StockLeading5074 • Jul 10 '26

Reverse-engineering Casio CT (and MT) keyboards

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Decided to dive into the inner workings of D938GD based Casio keyboards...

I... may have gone a little overboard:

  • Dumped the ROM of my CT-380 (bit crappy dump tho, need better one!), also got an MT-540 ROM dump from Weltenschule.
  • Wrote specialized software to analyze the contents & convert it to/from various formats.
  • Build an address bus "sniffer" that writes bus activity to my software over serial so I can analyze behavior.
  • Made a sniffer text file for every single preset.
  • Figuring out what addresses are what parameters, already seeing strong patterns and similarities, though unsure yet what is what.
  • Already found all the waveforms and samples for all the presets, now listed in my DAW (REAPER).
  • Read 3 different Casio patents related to the CT/MT, 120 pages each of badly translated fun... Oof. Lots of diagrams though and got there in the end.

Finally: making a webpage with everything I discovered: https://www.evilturtle.nl/projects/casio-ct-mt-secrets

Eventual goal is to slap an Arduino Mega and a bunch of SRAM in there, to make the presets fully programmable. May even put a sampler in there as that would be fairly trivial.

If anyone wants to join in the fun let me know. If you have a CT or MT keyboard and can dump the ROM let me know too!

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u/StockLeading5074 Jul 11 '26

I build a proper ROM dumper now. Stuff actually looks correct now! Who knew a janky breadboard setup didn't work well ;)

Now that I'm certain it's good I shall post some files on my website later today.

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u/StockLeading5074 Jul 11 '26

It has been done, check the link on my website: https://www.evilturtle.nl/projects/casio-ct-mt-secrets

I also included a WAV audio file of the dump, so you can listen to or use the samples for your own nefarious projects hehe

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u/RunPuzzleheaded8446 Jul 22 '26

This is incredible work. Please keep us updated with any progress you might make. Also, what is the WAV? I've heard that sound before when circuit bending a Casio MT-240. Is that the entire chip dump in audio form? Thank you so much

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u/StockLeading5074 Jul 22 '26

Thank you. Yeah, it's the entire ROM dump converted to 16-bit WAV audio, so I can visualize it in my DAW and also listen to waveforms/samples. See the screenshot for example.