NeoZeed
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SG1000 VDP
Posted: Sun Apr 23, 2000 4:44 pm
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Hi all,
I've start a sg1000 emu but i can figure out some spec of the TMS9918. It's about the VDP register ...
For example, i follow Zoop docs, i read that for obtaining the Tile starting address (reg4) i must (in mode 1) anded the value of the reg4 with 0x3f (so 6 bits) but when i look in the Tms pdf it says that only the first 3 bits are useful , why this mask of 6 bits (0x3f) ?? What's the technical reason for this ??
Thanks in advance
NeoZeed
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- Joined: 24 Jun 1999
- Posts: 1732
- Location: Paris, France
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Posted: Sun Apr 23, 2000 5:06 pm
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Quote > I've start a sg1000 emu but i can figure out some spec of the TMS9918. It's about the VDP register ...
> For example, i follow Zoop docs, i read that for obtaining the Tile starting address (reg4) i must (in mode 1) anded the value of the reg4 with 0x3f (so 6 bits) but when i look in the Tms pdf it says that only the first 3 bits are useful , why this mask of 6 bits (0x3f) ?? What's the technical reason for this ??
In don't have the answers handy, not even sure which is the good mask to use.
But in any cases, I suggest not trusting my doc at all. It is a draft I made sometime ago and I believe it's full of mistake.
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ATani
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Posted: Sun Apr 23, 2000 5:46 pm
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Quote > Hi all,
> I've start a sg1000 emu but i can figure out some spec of the TMS9918. It's about the VDP register ...
> For example, i follow Zoop docs, i read that for obtaining the Tile starting address (reg4) i must (in mode 1) anded the value of the reg4 with 0x3f (so 6 bits) but when i look in the Tms pdf it says that only the first 3 bits are useful , why this mask of 6 bits (0x3f) ?? What's the technical reason for this ??
>
If you want a fully working TMS9918 core check out Marat's old one which is included in his emulib i believe. If you want these files i think i have them still..
ATani
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NeoZeed
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Posted: Mon Apr 24, 2000 9:37 am
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Quote > In don't have the answers handy, not even sure which is the good mask to use.
> But in any cases, I suggest not trusting my doc at all. It is a draft I made sometime ago and I believe it's full of mistake.
In fact, i follow the Marat's code (emulib) with yours spec but i try to understand all what i read and there's some black point,... but i'll try to admit without understanding (damn..)
Thanks you all.
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