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From: charles@hpcvcd.UUCP
Newsgroups: comp.sys.amiga
Subject: Re: Monitor mishmash
Message-ID: <4410014@hpcvcd.HP>
Date: Thu, 29-Oct-87 18:20:21 EST
Article-I.D.: hpcvcd.4410014
Posted: Thu Oct 29 18:20:21 1987
Date-Received: Sun, 1-Nov-87 08:24:35 EST
References: <3113@ccicpg.UUCP>
Organization: Hewlett-Packard Co., Corvallis, Oregon
Lines: 21

> > 	I would dicker with the not cheap comment. Ever heard of interleave?
> > I also made this comment, until I realized that if you delay ram timings
> > through interleaving, You don't need fast rams.
> >	 UUCP: uunet!ccicpg!harald
> 
> I think maybe you do.  Consider for a moment the Amiga.  At 640 across by
> 4 deep, the Agnus chip is fetching data for Denise as fast as a 3.58MHz 
> DRAM can supply it, or real close.  If you want to double the scan rate
> (why you're building this thing in the first place), you're now fetching
> video information at 7.16MHz.  Or, put another way, one fetch every 158ns.
> And that's not leaving any time to put the data in there, via interleaving.
> Now you're down to about 79ns.  I think the video DRAM will be cheaper than
> the high speed static RAM you'd need for this otherwise.
> 
> Dave Haynie     Commodore-Amiga    Usenet: {ihnp4|caip|rutgers}!cbmvax!daveh

If you fetch 32bits at a time and deliver 4 bits per pixel, you only
have to read your RAM at 895KHz, even after doubling the scan rate.
With half of the time for CPU access, this leaves approx 500ns per
access.  Can you say cheap RAM?
	Charles Brown		hplabs!hp-pcd!charles