Re: [stella] Midified VCS...

Subject: Re: [stella] Midified VCS...
From: Oliver Achten <achten@xxxxxx>
Date: Thu, 22 Nov 2001 10:26:44 +0100 (MET)
Hello Chris!

> Wrong.  The video inside the chip is just a 7-bit number.  The only real
> CVBS thing there is the chroma delay, which is just a tapped delay line.
> All the analog voltage levels are created off-chip, on the motherboard.
> To represent 128 colors with RGB, you still need 7 bits, and then how do
> you split them?  You'd need 9 bits to split evenly between the 3 colors.
> And even then, you may not be able to reproduce the colors in the original
> palette.  Maybe, but I don't think it's worth the effort right now.

You don't have to make it so complex. Just output the 7bit color value, and
route it externally through a PROM, where the color values are hardcoded (for
both NTSC and PAL). Alternatively, if you want to do the RGB encoding
On-Chip, using an YUV DAC could simplify the On-Chip decoding, but you would need
more pins (9 color bits, as you said, and the 3 luma levels), and YUV decoders
are not that cheap... So the PROM Method would be more effective.

> Yes, I'm writing my thesis on this chip.  I'll reprouce the chip in some
> form, and the paper will be *very* detailed, and *very* complete.

That sounds very great! :-)



GMX - Die Kommunikationsplattform im Internet.

Archives (includes files) at
Unsub & more at

Current Thread