M68K and Genesis VDP cheat sheets now available

Ask anything your want about Megadrive/Genesis programming.

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cmjrd2k
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Posts: 2
Joined: Thu Mar 15, 2018 4:34 am

M68K and Genesis VDP cheat sheets now available

Post by cmjrd2k » Sun Mar 18, 2018 12:47 am

Hi all,

I'm new here and pretty much a newbie to programming on the Genesis /Mega Drive. Two of the biggest hurdles have been for me so far: 68000 programming, and making sense of all the different VDP registers.

I couldn't really find anything that brought that information together in a tiny, compact way suitable for memorization study. So, taking from sources like sega2f and MarkeyJester' s detailed information on cycle timings, I've taken a first shot at making some "cheat sheet" documents.

These are works in progress, and would gladly accept error reports or suggestions.

The Ultimate 68000 Cheat Sheet will print on 5 double-sided A4 pages, which can then insert into clear files for easy study. The Ultimate Genesis VDP cheat sheet will print on 2 double-sided pages.

Anyway, here they are for now:
https://sites.google.com/site/carljr174 ... ects=0&d=1
https://sites.google.com/site/carljr174 ... ects=0&d=1

Or for more information of my foray into Mega Drive programming:
http://www.carlmuellerjr.com

Hope these are helpful to some people. Thanks, Carl

Iridon
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Posts: 3
Joined: Sat Mar 10, 2018 9:52 pm

Re: M68K and Genesis VDP cheat sheets now available

Post by Iridon » Sun Mar 18, 2018 7:02 pm

Just entered here so I guess I will say thank you as I will highly likely hit the same wall as you :)

Thanks!

Chilly Willy
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Joined: Fri Aug 17, 2007 9:33 pm

Re: M68K and Genesis VDP cheat sheets now available

Post by Chilly Willy » Thu Mar 22, 2018 1:23 pm

Those PDFs are slick! Thanks for making those, even if some of us probably don't need them. They make a nice reference tool.

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Miquel
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Posts: 437
Joined: Sat Jul 30, 2016 12:33 am

Re: M68K and Genesis VDP cheat sheets now available

Post by Miquel » Sat Mar 24, 2018 7:42 pm

Great work! I'm in love with it.
But it lacks to explain what are those 3 main numbers, I suppose that are 8/16/32 bit cpu access but a rookie doesn't need to know this.

An still, I'm pretty sure that there is a few formulas to explain all those numbers in a even much more compact form, a formula that makes sense of all this, and helps memorize it.

cmjrd2k
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Posts: 2
Joined: Thu Mar 15, 2018 4:34 am

Re: M68K and Genesis VDP cheat sheets now available

Post by cmjrd2k » Sun Mar 25, 2018 10:04 pm

The 8/16/32 is there to show the cycle counts at different bit-widths. It also shows when instructions are unsupported at different bit-widths, by including a "--" in the appropriate column.
There probably is a simpler way to explain how the cycle counts work, but I think there are too many exceptions and it would end up being more confusing than helpful I like having every instruction laid out like this, it also lets you know what combinations of addressing modes are possible.

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