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Zerosquare

8 Millions De Couleurs Seulement ?

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Zerosquare    10

[Français]

En jetant un coup d'œil au schéma de la Jag pour trouver comment utiliser le mode entrelacé, j'ai découvert un truc bizarre : la sortie B0 de Tom est reliée à un point de test, et l'entrée B0 du DAC vidéo est reliée à la masse, ce qui veut dire qu'il n'y a que 7 bits de résolution affichés pour le canal bleu (au lieu de 8) :huh:

 

Atari nous a-t-elle menti à propos des 16 millions de couleurs, ou est-ce que c'est une erreur sur le schéma (ou une version préliminaire) ? J'ai la flemme de démonter ma Jag maintenant pour vérifier -_-

 

 

[English]

While peeking at the Jag's schematic to find out how to use the interlaced mode, I found out something weird : Tom's B0 output is connected to a test point, and the video DAC's B0 input is connected to ground, which means there are only 7 bits of resolution displayed for the blue channel (instead of 8) :huh:

 

Did Atari lie to us about the 16 million colors, or is it a schematic error (or a preliminary version) ?

I'm too lazy to take my Jag apart now to find out -_-

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GT Turbo    4

That's a nice question Zero ;)

 

But it's only for 24 bit mode, i don't know if somebody want to use it, too much problems and restrictions. And you know what ? Not enough people can see the difference between 8 and 16 millions of colors, except you ( ;) )

 

I don't know if this modify something in other video mode, but you've seen it, and Atari was a specialist in this kind of thing :P

 

 

GT :poulpe:

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SCPCD    0

Yes, it's true, the bit 0 of the Blue color is not used probably because of the use of a SIL resistors that have note enough pins :(

but your TV couldn't draw all 16millions colors :P

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Hmm... interesting... question...

I always wonderedhow accurate the schematics are... but we can never be sure since its just to much work to trace all of the lines.. anyhow..

 

sure noone can se difference between 8 & 15milj colors.. BUT...

 

It would defenitely be possible to se difference if ONLY blue was used!... say draw a screen size shaded line, from black to full blue... then the "increments" should defenitely be seen with 7bits (127 shades) ...and it should be smoot on a full 8bit blue...

 

(I remember this from playing with APEX color modes for the falcon... teh TC mode was never as good as their interlace "24bit mode" ..(interlaced 256colors). Similar should be possible to determine on the jaguar... (if now anyone cares =) ....well.. ok... now with the CF 720*480 24bit images would be possible... (since they eat up to much memory otherwise :)

 

 

Hmm... speaking of i-lace.... ...i have an unreleased secret ;P ..waiting for the right moment...

 

cheers

/Sym

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Zerosquare    10
Hmm... speaking of i-lace.... ...i have an unreleased secret ;P ..waiting for the right moment...

Don't tell me you've figured it out... I've spent those last days on it, you'd spoil my fun :lol:

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..... ok i will not tell you :whistling:

 

:)

 

anything more than.. according to the ataris docs we have there is no way to turn it on...

 

No i will stop spoiling your fun ;) back to whistling...

 

:whistling:

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Zerosquare    10

And the answer is (for 50 Hz) :

 

move.w #624, $F0003E

($F0003E is the Vertical Period register)

 

I thought it couldn't be that simple (since almost nobody seemed to have done it before), so I spent several days searching information about video signals, and deciphering Atari's documentation... but that's it, and it works. ;)

 

Nothing wasted, though ; now I understand how to setup all the video registers, so if we need to tweak the resolutions, I can do it :)

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SebRmv    2
Nothing wasted, though ; now I understand how to setup all the video registers, so if we need to tweak the resolutions, I can do it :)

 

great!!

 

so you are volunteer to write the ultimate "set resolution routine" for the Jag :) ?

 

and by the way, if you have some time to write all your thoughts about this point in a document, do not hesitate :D !!!

 

Seb

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SebRmv    2
Yeah, I was thinking about both of those things... I'll see ;)

 

Oh Zerosquare :wub:

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And the answer is (for 50 Hz) :

 

move.w #624, $F0003E

($F0003E is the Vertical Period register)

 

I thought it couldn't be that simple (since almost nobody seemed to have done it before),

 

hmm... well if it were that simple I would not have had to waste some week on debugging it (when I was doing this (december -04).

 

And it is not as easy as just setting a register (like it is on the falcon).. atleast it was not for me...

 

And there are several ways to get "interlace" ..on the jaguar but only one of them will produce "True" interlace... that is an actual improvement in display quality due to the fact that the display is shifted half a scanline up/down on the TV.

You can se this if you write a interactive program that changes these things on user commands, and then sit with a lupe infront of the TV and stare at the RGB dots, press and se that they actually shift... 8) ...phuu it was no easy task for me atleast.... (this should actually be a separate topic, so i stop =)

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Zerosquare    10

So there is more to it ? Good thing, that was TOO easy :D

I'm getting back to work then ;)

 

(BTW, I'm cheating : I have a video capture card on my PC with custom drivers I've written, so I can debug this stuff easily without having to stand in front of the TV with a loupe :) )

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=)

 

Well i mean IF you can display a full gfx picture say 640x480 in nice interlace just by setting that register, then NO! there is no more work... (then i must have done something wrong, and wasted time finding a workaround for my own mistake)..

I guess Im, "between the lines" asking: can you display such a picture? =) just by setting that register?

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Zerosquare    10

Well... :blush:

 

I just checked that changing this register enables the generation of a proper interlaced video signal, using the code for a little demo from SCPCD as a framework...

 

BUT ;)

 

Displaying a high-res picture was my next step. I started playing with it yesterday night, but as this is my first piece of code on 68K and my first attempt at Jag programming, you can guess I'm a bit slow :P

 

So you are most probably right about it being more complicated than setting a single register.

 

Enough chatter... more code awaits :)

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