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From: portuesi@tweezers.esd.sgi.com (Michael Portuesi)
Newsgroups: comp.sys.amiga
Subject: Re: 4096 colors in HIRES
Message-ID: <PORTUESI.89Jul15232025@tweezers.esd.sgi.com>
Date: 15 Jul 89 22:20:25 GMT
References: <20069@cup.portal.com> <409@xdos.UUCP> <20112@cup.portal.com>
	<412@xdos.UUCP>
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In-reply-to: doug@xdos.UUCP's message of 4 Jul 89 17:30:28 GMT


In article <412@xdos.UUCP> doug@xdos.UUCP (Doug Merritt) writes:
   In article <20112@cup.portal.com> stephan@cup.portal.com (Stephen Derek Schaem) writes:
   >If you change the colors registers (384,000 times a second) you get you 4096
   > colors screen

   As I recall from previous discussions, you can't change that fast due
   to latency of response from the chip. Someone once said they'd calculated
   that you could change (I think) two colors in the palette per scan line
   in the horizontal retrace period, and if you tried to change more, you
   wouldn't finish in time for the next scan line. I never double checked
   this myself, but you certainly should check before committing to this
   approach.


Only two colors?  The Atari 800 has the capability to interrupt the
CPU at a particular raster position (very similar to the Amiga's
Copper, but only at the end of a raster scan line).  I remember that
even with the 1.79 MhZ clock on the Atari you could change three
colors reliably if you wrote your interrupt service routine tightly
enough.  I should think that you could change more colors in the
palette with the Copper, though all 32 seems pretty unlikely.

Of course, I could simply be spewing rubbish.

			--M