My goal is to recreate the TurboGrafx at gate-level, however there isn't much documentation of the system, probably due to its relative obscurity.

What I want to know is how long one word (processor instruction) is, for the system.

Obviously, I'm not expecting a flat number, just a general explanation.


1 Answer 1


The processor is a modified 6502 so one word is 8 bits. Many instructions are encoded as multiple words but for those the processor just fetches them in sequence when required.

I believe the graphics processors use a wider bus, hence the '16' part of the name.

  • yeah, that makes sense, actually. where can I find a list of processor instructions?
    – Badasahog
    Oct 16, 2018 at 17:37
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    @JackKasbrack archaicpixels.com/HuC6280_Instruction_Set looks right to me, at least on brief inspection. Also, re: the original 6502, see sources like atarihq.com/danb/files/64doc.txt for a cycle-by-cycle breakdown of instructions. Don't rely too strongly on the latter though, as the 65C02 that Hudson worked with contains some bug fixes and some changes in logic (e.g. to read, read, write rather than read, write, write when performing a read-modify-write) that could cause observable differences in a reimplementation.
    – Tommy
    Oct 16, 2018 at 17:59
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    Have a look at the Super Famicom, it's well documented and basically the same set up. 8 bit CPU with 16 bit extensions, 16 bit bus for the video chip.
    – user
    Aug 28, 2022 at 22:50

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