Re: [stella] The heart of darkness. (was midified VCS)

[Chris Wilkson <ecwilkso@xxxxxxx>]

On Sat, 17 Nov 2001, John Saeger wrote:

>
> ----- Original Message -----
> From: "Chris Wilkson" <ecwilkso@xxxxxxx>
>
> > Hmmm....everything looks digital to me.  Do you have any specific
> examples?
> > I mean, there are half pass gates, but it is afterall an NMOS process.

> Cool.  So it's a deterministic machine.  I suspected as much.  ;-)  I don't
> know what a half pass gate is.  But to cut to the chase, the part I'm
most
> interested in understanding is right on page one.  The horizontal motion

> How does it work?  I recognize the NAND gates and the NOR gates.  I don't
> recognize the FET looking thingys.  Can you write down a logic equation for
> just that one cell type?  Can you explain it in detail?  What does *A* mean?
> Why are there stars?

I've attached a hasty drawing of the cell in question.  Those are indeed
FETs.  That is a "half" pass-gate.  Basically, it's a switch.  Think
"tristate output".  The "A" means that it's the smallest standard gate
size.  Take a look at the last page for the actual sizes.  Because they
are located after a passgate, near a node with no other input, I'm assuming
the "*" means that the node can be in an undriven state.  That is certainly
the case here.

Now...I don't know what this circuit actually does.  Yet.  This section of
the chip is one of my lowest priorities at the moment.  But hopefully, this
information will allow you to dig through it yourself.

-Chris

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Description: TIA cell