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I recently bought a Sharp EL-9950 graphing calculator (which is considerably rare compared to the other brands). I have a copy of its OS upgrade file, which is essentially ROM dump for the new version (or at least I think it is).

I searched everywhere, but I couldn't find any info about the hardware of this calculator, and it was too expensive for me to try opening its case.

How do I go about reverse engineering the ROM dump (exactly 1MB) to determine at least which instruction set it uses (so I can format it with my own ROM someday, I guess?)

Thanks!

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  • try to disassemble the binary using various disassemblers and if the "program" that comes out of it is nonsense then it's not a rom for that cpu. Commented May 4, 2017 at 12:35
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    Have you tried binwalk --opcodes ?
    – perror
    Commented May 4, 2017 at 12:59
  • ratchet: Yes, I tried to disassemble it as ARM and others but sorry, it was to no avail. perror: Thanks, I will try it right now. Commented May 5, 2017 at 13:29
  • Sorry, but binwalk does not give ANY result. I ran it in Ubuntu. --opcodes gives literally nothing. Commented May 5, 2017 at 14:04

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My low-tech approach has been to build a list of n-grams (n=3,4,5,6) and look for the most common sequences in a corpus of samples for different architectures (if you happen to have one).

Sometimes even searching on Google for the hex byte sequence can give some hints.

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