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  • Joined: 30 Jun 2016
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VDP Registers that do nothing
Post Posted: Mon Aug 23, 2021 3:37 pm
So I've been chatting with a friend about the Mega Drive VDP, and how it has a bunch of debug registers that people are still figuring out exist, and what they actually do.

So, naturally, the discussion wandered towards the Master System VDP. And we went checking the relevant Wiki article.
It seems to cover all the bases, but I'm curious if the registers that do nothing actually do nothing on the Master System VDP?
The documentation is approaching over a decade and a half old at the time of this post, and I know the Mega Drive scene of the time definitely didn't know what the heck was laying hidden inside most Mega Drive VDPs.

I'm curious if there's hidden debug registers inside the Master System VDP that nobody's thought to fish out and analyse. Or if there really is nothing more to discover, and I'm just barking at a dead tree.
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Post Posted: Mon Aug 23, 2021 8:38 pm
Well, the wiki is cribbed from Charles MacDonald’s doc and it it covers the weird bit masking and various other undocumented and useless effects, so I think it’s fairly well researched. Perhaps there is a test register in there, and I’m not familiar with what the Mega Drive secrets are to know what it might enable.
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VDP Registers that do nothing
Post Posted: Tue Aug 24, 2021 2:05 am
We need to decap it and uncover all of its remaining juicy little secrets :)
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Post Posted: Thu Aug 26, 2021 4:20 am
Alright, thanks for the help!
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Post Posted: Thu Aug 26, 2021 9:46 pm
Flygon wrote
So I've been chatting with a friend about the Mega Drive VDP, and how it has a bunch of debug registers that people are still figuring out exist, and what they actually do.


I know there's additional VDP register bits for the Genesis 128K VRAM mode that we didn't know about until more TeraDrive reverse engineering was done a few years ago, and that functions of the VDP debug register at $C0001E have been more fully worked out, but are there others? Just curious.
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