RGB availablity inside the original 8-bit motherboards?

[jmccorm]

None of the Atari 8-bit machines have motherboard taps for RGB(+Sync), correct?

[thorfdbg]

Correct. The Atari chipset does not operate in RGB colorspace. They use the TV-typical luminance + color phase encoding.

 

[Level42]

Exactly. In 1979 it was already amazing (and a world's first) that the A8's had Y/C output (S-video as it was named later).

 

 

However, today you can add RGB output by a simple upgrade called Sophia.

 

The picture quality is breathtaking and I would fully advice anyone with a RGB CRT monitor or TV to get one.

 

There are some very very minor compatibility issues with demo's though. If you're anal about that, you can still watch the original video-output for just those few demo's that exploit these tricks. as this is also still available after installing Sophia

Edited September 11, 2018 by Level42

[1050]

From what I know they actually make RBG, luminance,

and sync first then marry it all into color phase

encoding. Those signals being GTIA's LUM0-3 respectively,

perhaps. Just a suspicion mind you - no facts can be

proven by me anyway. Somebody with moar better setup

might be able to smell around in there though.

 

I've seen a lot of TV circuits that take RGB with

sync and run it thru the 'double down' resistor

network scheme as in R47-50 to do the TV signal

generation with. Each resistor in that network is

half the value of what the previous one is for a

precise reason you see. What people can't fathom

is that within the following transistor's gain

function, FM modulation occurs with the color

phase signal and the results are the perfect marriage

made for TV use. Again can't prove it by me, to twist

a phrase.

 

Not a high priority issues that I will ever defend

either. You can think what you want over there just

as I'm going to do over here. rant/OFF

[Rybags]

No, the internals of GTIA are based on producing a colour signal which is just a phase delayed square wave I do believe.

The colour value selects an internal delay tap (with 0 just turning the waveform off ?)

There's (typically poorly reproduced) Atari GTIA schematic docs around that document it to some extent. Plenty more was gained by the decaps over the last few years.

External circuitry to GTIA massages the square into a semblence of a sine wave.

 

Also, somewhat annoyingly though in common with many other old computers, it appears the saturation value isn't tweaked with the luma which means low luma values are oversaturated and high ones are washed out.

[jmccorm]

Thank you all for your response. I'll keep my Atari SC1224 in its current role as a portable arcade monitor.