Atatri 2600 - Chroma Decode for RGB output (or one step further for DVI/HDMI)

[WhyLee commotari.club]

Hi Guys!

The Atari 2600 in NTSC and PAL version has 3 digital bits to output the Luma video signal ( = Y ) which is great to have it digitally.
However the chroma signal (CrCb) is a bit difficult to understand. I guess the TIA uses the timing from the color carrier (4,43MHz in PAL, 3,54 in NTSC) and does a QAM modulation.
I am not sure but I think, the TIA does not do any analog modulation of the 0° and 90° (sin and cos) component of the color carrier.
Maybe it does some phase shifting for the Cr and Cb signal and combines that to the chroma output?

Does anyone exactly know how the TIA chip does this? Or does it really have a kind of resisitor ladder DAC inside for Cr and Cb and combines that somehow?
Does anyone have a scope picture with that signal and the color carrier as a phase reference?

I am wondering if there is a way to make a reliable chroma decoder that at the end comes out with 2 bits for Cr amd 2 bits for Cy.

Is the internat color register of the TIA exactly a combination of  3 bit Y + 2 bit Cr + 2 bit Cb ?

If we can decode the Cr and Cb signal, then we might do an RGB decoding with some digital logic ==> R = Cr-Y;  B = Cr-Y ; G = 3Y - Cr - Cb
 

Then we could make a high quality RGB output, but not with a super complicated pcb (as it already exists).

Also if we have digital RGB, the way to DVI might also not be that far.

 

for HDMI maybe that could be done with one of these:

* ADV7513 from Analog Devices
* TFP410 from TI
* TDA19988 from NXP
* Sii902X from Silicon Image