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From: grr@cbmvax.cbm.UUCP (George Robbins)
Newsgroups: comp.sys.amiga
Subject: Re: Extra-Half-Brite
Message-ID: <2005@cbmvax.cbmvax.cbm.UUCP>
Date: Thu, 11-Jun-87 11:47:10 EDT
Article-I.D.: cbmvax.2005
Posted: Thu Jun 11 11:47:10 1987
Date-Received: Sat, 20-Jun-87 12:36:23 EDT
References: <3912@jade.BERKELEY.EDU>
Reply-To: grr@cbmvax.UUCP (George Robbins)
Organization: Commodore Technology, West Chester, PA
Lines: 68

In article <3912@jade.BERKELEY.EDU> spencer@eris.BERKELEY.EDU (Randy Spencer) writes:
> In article <341@esunix.UUCP> blgardne@esunix.UUCP (Blaine Gardner) writes:
> >Now that the A500 is in the stores the local Amigaoids are going nuts
> >over Extra Half Brite. This was discussed somewhat a month or so ago,
> >but would someone at C-A care to answer some questions?
> >
> >1) Do all A500s and A2000s have Extra Half Brite (EHB)?
> Yes!
> >2) Is EHB an officially supported video mode?
> Yes!
> >3) Will future color expansion interfere with EHB?
> No, EHB must be specified to get it, you don't just turn on 6 bit planes
> >5) Where can documentation on EHB (hardware and programming) be found?
> Addison Weseley (?)
> >6) Is it true that the new Aegis software supports EHB?
> Yes, they went whole hog
> >9) How can you distinguish an EHB chip from a non-EHB chip (by part
> >   number, revision number, or date code)?
> 
> I believe that all chips past rev 6? or 7 support it
> >-- 
> >Blaine Gardner @ Evans & Sutherland
> 
> 
> I personally was supprised to hear all the above.  The machine is not
> spec'ed to support 64 colors, and when I spoke to the Developer Support
> people in August last year they said that EHB was a fluke and not supported.
> I guess that they didn't want to start handing out all these extra chips
> so people could get the EHB in their Amiga.  I have 2 home Amigas and one
> at work and NONE of them have EHB.  Such is life!  I read something on 
> usenet or some such about it impeading future expansion, but when Dale Luck
> brought up EHB at the last Badge meeting I asked him point blank what the
> Amiga people thought of it, and he said that Amiga (commodore too?) has 
> ALWAYS supported EHB.  Hmmm... news to me, guess I need to buy me 3 new
> chips!

	The story is somewhat confusing.  EHB was added when a new revision
	of some of the custom chips made it into production.  It was a new
	feature, but there was no way for a customer to know whether any
	particular Amiga on the shelf would have it or not.  Also, while a
	user could theoretically order a replacement part to upgrade his
	system, both production and service had the old and new parts listed
	as interchangable, since either performed the advertised Amiga
	functions.

	The result was EHB not being supported in a "product" sense.

	The software has (since 1.2?) always supported EHB as an option that
	may be available and will continue to do so.

	There was some discussion about whether future Amiga chips would
	support EHB.  Basically, EHB is a kludge to let you get 64 colors
	despite the fact that you only have a 32 entry color lookup table.
	This might not make too much sense if some *hypothetical* future
	chipset were to implement a larger color lookup table.  Of course
	it should be possible for the software to emulate EHB with the color
	lookup table, or we might chose to leave EHB in for compatibility
	reasons.
 
-- 
George Robbins - now working for,	uucp: {ihnp4|seismo|rutgers}!cbmvax!grr
but no way officially representing	arpa: cbmvax!grr@seismo.css.GOV
Commodore, Engineering Department	fone: 215-431-9255 (only by moonlite)