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In article <10513@jarthur.Claremont.EDU>, rspangle@jarthur.Claremont.EDU
(Froot Loop) writes:
|> In article <634@bcstec.boeing.com> ruben@bcstec.boeing.com (Reuben
Wachtfogel) writes:
|> >There seems to be some confusion in the literature regarding this
|> >mode.  I've seen it described as a 16 color mode, a 64 color mode,
|> >a 4 or 16 color mode, and a 16 or 64 color mode in various online
|> >tech manuals, and my VGA card (Paradse)  manuals.
|> 
|> >3) Is there a 64 color 640x350 mode or isn't there ?
|> 
|> Not on any EGA or VGA card I can think of.  The 64 comes from the
palette.
|> On EGA cards, the red/green/blue values can each go from 0-3.  4^3 =
64
|> possible colors.  
|> 

At the risk of further confusing the issue, but in the interests
of trying to clarify Randy's point:

The IBM EGA card came in various memory configurations.  The cheap
version of the card had only 64KB or video memory.  The more usable
EGA cards came with 128KB of video memory.  Clone cards were known
to come with as much as 256K of video memory.

The 64KB EGA cards can support 320x200x16 and 640x200x16 because
those video modes only require 32K and 63K of video memory.  But
the 640x350 mode can only support 4 colors (using 55K of video
memory). 

The 128K EGA cards can easily support 320x200x16, 640x200x16.
And the 640x350x16 mode only needs 110K of memory.

EEGA cards (that come with 256K memory) usually support some extended
modes like 640x480x16 (150K) and 800x600x16 (234K).  Note that EGA
cards NEVER support more than 16 colors (and always out of a palette
of 64 colors).  Also note that these modes, tho similar to the VGA
modes,
use the EGA color palette (not the VGA color palette), and do not
work with VGA software that might appear to support them.

The digital signal applied to the EGA monitor consists of rgbRGB.  This
means that in general, an EGA monitor can display 2^6 distinct colors
on its screen, however the the programability of the colors in
software looks like iRGB (where the i bit is an intensity bit in text
mode), leaving the programmer access to only 16 colors out of the 64
the monitor can display.

The mapping done by the EGA board between the iRGB form and the rgbRGB
signal is done by treating the color palette as a 16 color field
containing an rgbRGB value the monitor should display for each iRGB
color.
The order of the colors in the palette is setable by the programmer.
For the sake of compatibility, most programs assume that the color
palette is loaded with a "standard" color mapping very close to
a physical interpretation of iRGB as a physical color signal.
(I think the -RG- color is actually closer to ORANGE than YELLOW,
because IBM didn't think people could tell the difference between
high and low intensity yellow!  IBM actually calls the low intensity
color: BROWN.)

Thus in graphics modes, ANY 16 colors can be chosen by the programmer.

In text modes, (someone correct me if I'm wrong here) the iRGB form is
fixed, the color palette is not used, and only 2 intensities of 8 real
colors are available (totaling 16 colors).  

There, I hope I haven't confused things TOO much  B^)

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