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From: cem@intelca.UUCP (Chuck McManis)
Newsgroups: net.micro.amiga
Subject: Re: Re: Amiga with a small monitor? -- (A fix for crummy text)
Message-ID: <138@intelca.UUCP>
Date: Fri, 8-Nov-85 15:14:05 EST
Article-I.D.: intelca.138
Posted: Fri Nov  8 15:14:05 1985
Date-Received: Mon, 11-Nov-85 05:47:39 EST
References: <298@caip.RUTGERS.EDU>
Organization: Intel, Santa Clara, Ca.
Lines: 77

> From: LLi.ES@Xerox.ARPA
> 
> Is there a hardware limitation which prevents the Amiga to send 640x400
> NON-interlaced to a monitor which can display at that resolution?  If
> so, where is the pinch point?
> 
> Leonard.

I asked a similar question a while back and follows is the reply from
Dale Luck of Commodore-Amiga. The problem is that AGNUS is not capable
of shoving the bits out to the video circuit any faster. This is a 
pretty common problem for most graphics hardware since there are 
lots of variables to account for when accessing the RAM data. ('frinstance
access time, whether or not a refresh is happening, and how many pixels
you get in one read.) This is necessated by the fact that the 68K shares
the memory that the video stuff uses and if you tried to get 640 X 400
4 bit pixels out to the monitor every 60th of a second there would take
a transfer rate of 7.68 Mbytes/sec leaving only 4% of the available 8Mhz
bus to the CPU and other peripherals. 

--Chuck McManis

------- Begin Forwarded Message ------
Date: Thu, 31 Oct 85 10:22:18 pst
From: sun!decwrl!pyramid!amiga!dale%tooter (Dale Luck)
Subject: Re: Resolution and Flicker - Rumors/Solutions
Organization: Commodore-Amiga Inc., 983 University Ave #D, Los Gatos CA 95030
Cc: 

If you think this is of interest to the rest of the net.micro.amiga please
post it.

You conceptually split the graphics hardware into two areas:

1 raster operations and generation of bitmap.
2 conversion of bitmap to video stream of display on monitors.

details of 1.
AGNUS (blitter chip) is currently capable of blitting, linedrawing,
areafilling,floodfilling,clearing,text in max 1k X 1k bit area.
(k = 1024 in this discusion)
Couple this with AGNUS's maximum address range of 512k bytes.
A 1kx1k image is 128k bytes.  So it seems that a maximum of 4 bitplanes
at this resolution would fit.  This however leaves no room for disk buffers,
copperlists, sprite buffers, audio buffers, all of which need to reside in
this lower memory.

details of 2.
The display hardware (AGNUS & DENISE) were designed to put out standard
NTSC scan rates of pixels.  We extended it do go double horizontal
resolution by relying on rgb monitors for crisp display, and an excellant
motorola rgb to ntsc chip that does good filtering to remove much of the
color aliasing.  AGNUS can only display a theoretical maximum of about
240 non-interlaced lines or about 480 interlaced lines. (The actual numbers
maybe 230 and 460).  Horizontally AGNUS/DENISE can display nearly 350/700
pixels by stretching data fetch starts and stops. You however need a good
rgb monitor to see this.  The graphics.library allows you to specify display
regions up to this sizes as well as split your screen into several displays.
However the current version of intuition only allows displays of the size
320/640 horizontal 200/400 vertical.

The display hardware is capable of dealing with bitmaps up to 64k x 64k.
It however can only display as many pixels as the above paragraph
describes. You can smooth scroll around in the larger bitmap though to
help get around the lack of resolution.
We are not saying this is the answer for everyone's problems, we do not
want to over spec it, just present the facts. If you can use to help you
in your work and play, and you get one, I hope we don't disappoint you.
Thanks,
 Happy hacking
   Dale Luck

-- 
                                            - - - D I S C L A I M E R - - - 
{ihnp4,fortune}!dual\                     All opinions expressed herein are my
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