19 Jan
2006
19 Jan
'06
12:12 p.m.
On 1/18/2006 at 5:08 PM ard at p850ug1.demon.co.uk wrote:
Yes, I noticed that last night when I did a little bedtime reading.
I doubt it. I seem to rememebr a PROM in the input
stages of the 5154
monitor, which may well have done the same conversion, though.
Darn--you're right. On page 4 of the EGA display tech ref, there's a table
that says "When operating in Mode 1, the display maps the 4 input bits into 16 of the possible 64 colors as shown in the following
table" While bright
yellow (color 14) is given as RrGgb, color 6 is given as Rg (brown),
where dark yellow would be RG. How very strange to special-case it in the
monitor! Probably done because the EGA could drive a CGA monitor and
that already had the brown special-casing.
Yes. The EGA card could drive a CGA monitor in the 16 colour modes, and I
guess it made more sense to make the EGA monitor compatible with the
CGA-like signals than to have duplicated modes in the card, one set for
the CGA monitor, the other for the EGA monitor.
At which point the EGA monitor pretty much has to do the brown-kludge for
compatabiliity.
I'm not inclined to check the PGA BIOS, but the PGA display appears not to
do the color re-mapping.
IIRC the PGA monitor has analogue inputs, and does what you'd expect.
Alas my PGA techref doesn't contain the BIOS source or the source for the
firmware for the 8088 on the card. Actually, _is_ there a BIOS for the
PGA card? It's been a long time since I read that techref, but I thought
it exactly emulated the CGA card and would therefore use the normal CGA
bios (in the mainboard ROMs). To do anything more fancy you loaded
special software from disk.
Again a guess, but I would think the PGA card does some sort of
brown-kludge in the colour lookup tables when doing the CGA emulation.
-tony