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View topic - VDP Register $00 - Settings Scheme

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  • Joined: 27 Mar 2023
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VDP Register $00 - Settings Scheme
Post Posted: Thu Mar 30, 2023 4:51 pm
Hi SMS enthusiasts :)

I've been interested in developing on Master System for a little while, but so far I haven't gone into that much, now I'd like to get into it a bit more seriously.

As there are many things to know, I make little memos to help me understand better, visualize better and memorize better.
I made various diagrams, but here I wanted to have your opinion on a diagram that I made for the settings of Register 0 of the VDP.

I have a doubt about bit 1:
- According to SEGA it must always be set to 1 in mode 4.
- According to the "Charles MC Donalds" doc, it changes the height of the screen from 192 to 224 lines.
- According to the "Richard Talbot-Watkins" doc it extends to 33 columns of "LARGE", an error?
The rest looks good to me.

Please tell me if there are any errors, if I can improve things, and so it can be useful to the community of developers on Master System :)

Thanks

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  • Joined: 06 Mar 2022
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Post Posted: Thu Mar 30, 2023 8:05 pm
Loving this visual reference!
Nice work!

Just one very minor thought - your sprite shift kind of looks to me like sprites are shifted to the right. Perhaps the "solid" sprite should be on the left and the ghost one on the right?
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Post Posted: Thu Mar 30, 2023 8:44 pm
Thank you very much.
Yes, you're right, I wanted to mean the shift to the left with the ghost, but finally with your remark I see that it's not logical.
Thank you, I'll change that. Do you have an idea about bit 1?
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Post Posted: Thu Mar 30, 2023 9:00 pm
Sorry I overlooked that question.
As far as I know bit 1 controls the 24 vs. 28 line switch - I can't really see how the VDP would be capable of 33 columns from what I know about it.

The official Sega guide recommends you fix some settings I think just to keep things simple. I would trust Charles's guides above all else by default, they are very comprehensive.
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Post Posted: Thu Mar 30, 2023 9:38 pm
thank you again for your answer. Yes me too it seems to me to be an error on the doc "Richard Talbot-Watkins", I will follow your advice and also study the doc of "Charles MC Donalds" even if that of Richard is excellent. I see them as complementary on certain points.
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Post Posted: Thu Mar 30, 2023 9:56 pm
In which case would there be an interest in using the sprite offset of 8 px?
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Post Posted: Fri Mar 31, 2023 2:53 am
tetsuro wrote
In which case would there be an interest in using the sprite offset of 8 px?

The theory goes (in the official Sega manual) that you can use bit 3 to smoothly transition sprites off the left hand edge of the screen, whereas they naturally transition off the right hand edge due to their origin being in the top left corner of the sprite.

However in practice I'd say it's often more convenient to set bit 5 to blank the left column and have sprites move smoothly off both edges of the screen. Bit 5 kind of needs to be set if you're horizontally scrolling anyway,because the left hand edge displays a bit unintuitively in horizontal scroll, and once set there's not much reason to use the sprite shift.
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Post Posted: Fri Mar 31, 2023 9:56 pm
Thank you for your details willbriton, I see better.
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