Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!usc!apple!oliveb!amiga!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Chip memory bandwidth, graphics modes
Message-ID: <9213@cbmvax.commodore.com>
Date: 4 Jan 90 22:26:22 GMT
References: <14120@grebyn.com>
Organization: Commodore, West Chester, PA
Lines: 29

in article <14120@grebyn.com>, ckp@grebyn.com (Checkpoint Technologies) says:

> 	I have this odd theory, though, that when Jay left Amiga he took
> a lot of the custom-chip knowledge with him, and that Commodore has only
> recently (if at all?!?) figured out how they work.  This would explain
> the length of time it took to get the mildly-Enhanced Chip Set
> produced, and some of the oddities: Only 64 colors in super-hires? That
> could be because they couldn't figure out how to double the speed
> of the color palette registers in Denise.

Neither could Jay.  Color registers have always run at the 320 pixel/15 kHz 
dot rate.  When you're in a 640 pixel/15 kHz dot rate, the 32 lores color
registers magically become 16 hires color registers; eg, they're multiplexed.
Now enter the new stuff, like 640 pixels @ 31kHz.  Everything must go twice
again as fast.  Another level of multiplexing is introduced, only for speed
it's introduced as late in the pixel path as possible.  The speed problems
are entirely a function of the rather ancient NMOS technology the chips are
built from.  Facts are, the original Amiga folks stuffed about as much goop
as possible into that 4 micron NMOS before ECS ever came along.  So there
wasn't much room left inside to add stuff; you hit very real limits on the
size of NMOS chips based on heat factors if nothing else.  That's why all the
new stuff happening just about everywhere is CMOS, even though CMOS is more
complicated.


-- 
Dave Haynie Commodore-Amiga (Systems Engineering) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
                    Too much of everything is just enough