Re: [stella] Midified VCS...

Subject: Re: [stella] Midified VCS...
From: Chris Wilkson <ecwilkso@xxxxxxx>
Date: Wed, 21 Nov 2001 11:23:43 -0500 (EST)
On Wed, 21 Nov 2001, Oliver Achten wrote:

> Wasn't it said to have about 5000 gates? Can't imagine that it has nearly
> three times as many gates as the 6502 (considering the simplicity of the

I've heard both numbers.  And I've guessed about 1000-2000 transistors.
But I haven't gotten far enough into it to know.  I can say that my numbers
are WAY too low.

> design). You yould also simplyfy it by abadoning the old CVBS logic in favour of
> having an rgb output (which would be much simpler).

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.

> Again, what kind of logic do they use? To what level of abstraction are the
> schematics drawn?

The chip is NMOS.  The schematics are gate level, but there are random single
transistors floating around as well.

> I hope you'll be succesful and that you will be in the right mood to write a
> nice documentation about it....  ;-)

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.

> Are there any chances for a person not living in the states to have the
> schematics?

As mentioned here several times, you should contact Curt Vendel.  I don't
have his contact info though....


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