Newsgroups: comp.unix.sysv386
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!ira.uka.de!fauern!NewsServ!!roell
From: roell@informatik.tu-muenchen.de (Thomas Roell)
Subject: VGA & CLUT (RAMDAC)
Message-ID: <1991Mar21.131423.11234@Informatik.TU-Muenchen.DE>
Sender: news@Informatik.TU-Muenchen.DE
Organization: Inst. fuer Informatik, Technische Univ. Muenchen, Germany
Distribution: comp
Date: Thu, 21 Mar 1991 13:14:23 GMT
Lines: 30

As perhaps some of you know, there are three different Color Lookup Tables
built onto a VGA boards. They all differ in the number of bits that are used
to specify a color:

471/171:	8 bits per gun
476/176:	6 bits per gun
478:		6/8 bits per gun

Normally you'll find on a VGA the 476/176. But there are some new boards
(Orchid Prodesigner II) that use the 478. As I saw from the pinout there is
one pin responsible to switch between 6 and 8 bits per gun. 

So far so good. But there also seem to be the possibilty to switch modes
without hardware assistance by writing a specific io-sequence to this chip.
This is what happened to some users of X386 while displaying gif-pictures
with xloadimge.

My question is now: Has someone informations about this chip, and how can I
exactly switch modes (not by accident as with xloadimge) ?

Another topic is that I whatched on the CeBIT a VGA that uses a special
CLUT (from Sierra) which can do 32768 colors (truecolor). Where can I get
this CLUT & docs ?

- Thomas
--
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