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From: bryce@COGSCI.BERKELEY.EDU (Bryce Nesbitt)
Newsgroups: comp.sys.amiga
Subject: Re: Amiga 500: a nice unit.  Way to go!
Message-ID: <8706182215.AA08958@cogsci.berkeley.edu>
Date: Thu, 18-Jun-87 18:15:24 EDT
Article-I.D.: cogsci.8706182215.AA08958
Posted: Thu Jun 18 18:15:24 1987
Date-Received: Sun, 21-Jun-87 17:26:33 EDT
Sender: steve@ucbvax.BERKELEY.EDU
Lines: 34
Keywords: Amiga 500. Its about time.
Summary: Colorburst, COLORON and gb_system_blpcon0

In article <> keithd@cadovax.UUCP (Keith Doyle) writes:
>
> I'll add a second [A-500 gripe].  It seems to me that the lack of a color
> NTSC output is a mistake. [...]

	When I first heard of this I was surprised.  What reason could there be
for hardware-disabling colorburst on the connector when there was already a
bit to do that on the custom chips?? (Almost as good)
	In fact, it should have been even easier...  The COLORON bit is a part
of gb_system_bplcon0, that magic location that gets or'ed into all copperlists.
What this means is that setting that would turn burst off for all screens,
clearing it would add burst.  Sort of like Interlace.
	For the default of the Amiga 500 you would turn burst off.  Anyone that
wanted color could change that state.

	That was theory.  Reality is somewhat removed.  While COLORON's nearby
neighbor, INTERLACE works as planned, the COLORON bit gets and'ed out when the
copperlists are rebuilt.  The result is that a little utility I wrote to
twoggle burst does not.  The little copper list scanner that came next
DOES work, but any utility that directly mangles copperlists is far too dirty
in INTENTION to actually release.

	This has only been tested on an Amiga 1000, if the 500's connector is
actually monochrome, then there is no need to even TRY to switch burst on and
off.
---------
	Ack!  (NAK,EOT,SOH)
|\ /|  .
{o O} . bryce@cogsci.berkeley.EDU -or- ucbvax!cogsci!bryce
( " )
  U	Single-tasking?  Just say *NO!*

Try twiddling ALL the bits in a copper MOVE to blpcon0 instruction.  Some
combinations of the upper bits have interesting side effects.