18 Jan
2006
18 Jan
'06
2:03 p.m.
There is a bit of a spat going on in a few forums regarding color index
#6 of IBM CGA. The old-timers know that it is brown from experience and
existing working hardware; the newbies (writing or using emulators) are
unwilling to accept that and are instead making CGA palettes with dark
yellow instead of brown.
Can anyone give me the history on why #6 is brown? Was it a design
mistake, or intentional? Is it a property of the monitor or something?
I can't find anything of substance to offer the newbies to convince them
otherwise; digital photos can be accused of being doctored or
miscalibrated (and yet is a digital photo showing "yellow" that started
this whole thing). About the only thing I can think of to offer as
proof is that the text colors in the VGA palette show brown, and IBM
wouldn't have done something like that by mistake -- or were they
perpetuating a mistake?
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Want to help an ambitious games project? http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
18 Jan
18 Jan
11:56 a.m.
There is a bit of a spat going on in a few forums regarding color index
#6 of IBM CGA. The old-timers know that it is brown from experience and
existing working hardware; the newbies (writing or using emulators) are
unwilling to accept that and are instead making CGA palettes with dark
yellow instead of brown.
Can anyone give me the history on why #6 is brown? Was it a design
mistake, or intentional? Is it a property of the monitor or something?
You are going to love my inital answer. Colour 6 is both dark yellow
_and_ brown.
As usual, I am going to look at the hardware side of things. I am also
talking solely about true-blue IBM stuff.
Let's start on the CGA card itself. I am going to assume text mode (about
the only place you'll get colour 6 on a real CGA card), the colours are
therefore determined by the attribute byte for each character. The
attribute data from the vieao RAM is latechs in U35 ('273). The outputs
of that go to a 4-bit 4-way multiplexer (U9, U10, '153), which, selects
one set of 4 bits or the other depending on wheter that particular dot in
the characer cell is set or not (OK, there's a lot more to it, blink
mode, graphics modes, etc, but I don't want to have to explain all 6
pages of the schematic at this point).
The outputs from that mux are latched again (U101, '174), then buffered
and sent to the DE9 socket.
So the card outputs the 4 bits _unchanged_ from the appropriate part of
the attribute byte. And it's clear from the circuit that the bits are :
Bit 0 : Blue
Bit 1 : Green
Bit 2 : Red
Bit 3 : Intensity.
So you could reasonably claim that 0110 was dark yellow and 1110 was
light yellow. But IBM also include the following table (suitably
re-formatted):
I R G B
0 0 0 0 Black
0 0 0 1 Rlue
0 0 1 0 Green
0 0 1 1 Cyan
0 1 0 0 Red
0 1 0 1 Magenta
0 1 1 0 Brown
0 1 1 1 White
1 0 0 0 Grey (=='light black' ;-))
1 0 0 1 Light Blue
1 0 1 0 Light Green
1 0 1 1 Light Cyan
1 1 0 0 Light Red
1 1 0 1 Light Magenta
1 1 1 0 Yellow
1 1 1 1 High Intensity White (=='light white')
OK, so why the odd name for colour 0 1 1 0. Well, we now turn to the
schematic of the CGA monitor. The 4 bits come in, and are buffered by
74S05 chips , Q201 and Q253 on my schematic. Now for the interesting bit.
There are 4 of the open-collector inverters -- Q201d., Q201f, Q253e and
Q253f -- whose outputs are connected together. This common signal will
only be high if the input signals are (wait for it) I=0, R=1, G=1, B=0.
That is, for this particular colour 6. For that colour, Q206 (a normal
NPN transistor) is therefore turned on, and this will reduce the level of
green in the final display. In other words this colour is a little redder
than you might expect.
I did say I'd only consider IBM stuff. But I will just mention that I've
worked on clone monitors that used a '138 to decode the input signals and
detect colour 6. I don't have any schematics to hand, though. And later
monitors still often used a PROM to decode the input signals, possibly
allowing several colour sets, and used 2 or 3 bit resistor DACs to feed
the CRT driverr stages. Now what that PEOM contained, and whether colour
6 was still special, I don't know.
So, to sum up :
1) IBM call that colour 'brown' in the CGA TechRef description
2) The CGA card doesn't do anything special with it, the obvious pattern
of bits appears on the DE9 connector
3) But the monitor does. It contains circuitry to shift that colour a
little towards the red.
I don't think this is a historical accident.
Hope that helps.
-tony
9:47 p.m.
In addition to the BROWN v Yellow,
there were differences in the handling of BRIGHT BLACK.
(Joe Campbell borrowed a "real" CGA card from me when he
found out that his Corona did not give the same color as IBM.)
--
Grumpy Ol' Fred cisin at xenosoft.com
19 Jan
19 Jan
3:13 p.m.
In addition to the BROWN v Yellow,
there were differences in the handling of BRIGHT BLACK.
(Joe Campbell borrowed a "real" CGA card from me when he
found out that his Corona did not give the same color as IBM.)
Surely any differences were in the monitor. Given that there are 16
possible colours, and 4 bits on the output DE9, it's hard to see how the
purely-digital card could make any difference.
-tony
7:19 p.m.
> In addition to the BROWN v Yellow,
> there were differences in the handling of BRIGHT BLACK.
> (Joe Campbell borrowed a "real" CGA card from me when he
> found out that his Corona did not give the same color as IBM.)
On Thu, 19 Jan 2006, Tony Duell wrote:
Surely any differences were in the monitor. Given that
there are 16
possible colours, and 4 bits on the output DE9, it's hard to see how the
purely-digital card could make any difference.
What SHOULD bright black on black (08) do?
What foreground color?
what background color?
20 Jan
20 Jan
7:18 p.m.
> In addition to the BROWN v Yellow,
> there were differences in the handling of BRIGHT BLACK.
> (Joe Campbell borrowed a "real" CGA card from me when he
> found out that his Corona did not give the same color as IBM.)
On Thu, 19 Jan 2006, Tony Duell wrote:
Surely any differences were in the monitor. Given
that there are 16
possible colours, and 4 bits on the output DE9, it's hard to see how the
purely-digital card could make any difference.
What SHOULD bright black on black (08) do? From the card, it should output R=0, B=0, G=0, I=1.
It's hard to see how
any CGA _card_ would do otherwise.
What foreground color?
what background color?
That's somewhat meaningless. The monitor should display a dark grey if
given those inputs.
Oh hang on... You're thinking of the blink bit, right? There's a bit in
one of the setup registers that turns the intensity bit of the background
colour into a blink-control bit. I would _guess_ without looking at the
card that 1000 as a forground colour is dark grey, 1000 as a background
colour is eitehr dark grey (if blinking is disabled), or black with
blinking forground if blinking is enabled.
-tony
18 Jan
18 Jan
11:52 p.m.
Tony Duell wrote:
So, to sum up :
1) IBM call that colour 'brown' in the CGA TechRef description
2) The CGA card doesn't do anything special with it, the obvious pattern
of bits appears on the DE9 connector
3) But the monitor does. It contains circuitry to shift that colour a
little towards the red.
I don't think this is a historical accident.
Thank you for that definitive answer!! I really appreciate it!
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Help our electronic games project: http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
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19 Jan
19 Jan
12:02 a.m.
Tony Duell wrote:
I don't think this is a historical accident.
Wait a second -- while your explanation very completely explains HOW, it
does not explain WHY. Why did IBM go through all that trouble to turn
#6 brown?
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Help our electronic games project: http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
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12:48 a.m.
On 1/18/2006 at 11:02 PM Jim Leonard wrote:
Tony Duell wrote:
I'd love to know for certain!
One can conjecture several plausible answers (e.g., brown is a more useful
color than dark yellow). I'm trying to remember if the 5153 was made in
Korea for IBM. If so, by whom?
Cheers,
Chuck
I don't think this is a historical accident.
Wait a second -- while your explanation very completely explains HOW, it
does not explain WHY. Why did IBM go through all that trouble to turn
#6 brown? 
7:41 a.m.
On 19/01/06, Jim Leonard <trixter at oldskool.org> wrote:
Tony Duell wrote:
Maybe it's just because they already had a yellow and no brown.
Dan
I don't think this is a historical accident.
Wait a second -- while your explanation very completely explains HOW, it
does not explain WHY. Why did IBM go through all that trouble to turn
#6 brown?
-- 
9:51 a.m.
Wait a second -- while your explanation very
completely explains HOW, it
does not explain WHY. Why did IBM go through all that trouble to turn
#6 brown?
My bet, at the time, it was popular to display little "landscapes" as
part of system demos. Lower third of the screen green (for grass)
upper two thirds blue (for sky) some kind of small building represented
in red (for bricks) and... a tree. You need brown for the trunk.
25 Jan
25 Jan
8:03 p.m.
wait a cotton picking minute...isn't there a reference
in "Revolution in the Valley" to a game written by
Bill Gates with a big BROWN donkey??? I don't own the
book, obviously stating from memory. Maybe someone can
confirm or deny.
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Wait a second
-- while your explanation very
completely explains HOW, it
does not explain WHY. Why did IBM go through all
that trouble to turn
#6 brown?
My bet, at the time, it was popular to display
little "landscapes" as
part of system demos. Lower third of the screen
green (for grass)
upper two thirds blue (for sky) some kind of small
building represented
in red (for bricks) and... a tree. You need brown
for the trunk.
27 Jan
27 Jan
8:30 a.m.
At 07:03 PM 1/25/2006, Chris M wrote:
wait a cotton picking minute...isn't there a
reference
in "Revolution in the Valley" to a game written by
Bill Gates with a big BROWN donkey??? I don't own the
book, obviously stating from memory. Maybe someone can
confirm or deny.
Story and screen captures at http://en.wikipedia.org/wiki/DONKEY.BAS .
Doesn't look brown to me. Maybe it's a question of the emulation -
which brings up full circle.
- John
8:12 p.m.
John Foust wrote:
Emulation pix at wikipedia are incorrect; color palette would indeed
make the donkey brown. If I cared more I'd update the donkey.bas
wikipedia article, but I don't :-)
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Help our electronic games project: http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
A child borne of the home computer wars: http://trixter.wordpress.com/
wait a cotton
picking minute...isn't there a reference
in "Revolution in the Valley" to a game written by
Bill Gates with a big BROWN donkey??? I don't own the
book, obviously stating from memory. Maybe someone can
confirm or deny.
Story and screen captures at http://en.wikipedia.org/wiki/DONKEY.BAS .
Doesn't look brown to me. Maybe it's a question of the emulation -
which brings up full circle.
19 Jan
19 Jan
3:17 p.m.
Tony Duell wrote:
I think you misuderstood me. My comment was intended to mean that it's
not a historical accident that the colour 6 looked brown on the original
CGA monitor -- for example that the phosphors used and the greyscale
setup gave that effect. There was a deliberate attempt to make the colour
look brown.
As to _why_, I can't say. I can only look at the scehamtics and tell you
what happens. I don't have a link to the brains of the designers :-)
-tony
I don't think this is a historical accident.
Wait a second -- while your explanation very completely explains HOW, it
does not explain WHY. Why did IBM go through all that trouble to turn
#6 brown?
12:12 p.m.
At 10:56 AM 1/18/2006, Tony Duell wrote:
You are going to love my inital answer. Colour 6 is
both dark yellow
_and_ brown.
As usual, I am going to look at the hardware side of things. I am also
talking solely about true-blue IBM stuff.
What? No discussion of the frequency curve of the tube's phosphor,
and whether this matches cultural perceptions of "yellow" and "brown"
when driven at those levels? :-)
- John
18 Jan
18 Jan
2:10 p.m.
[...]; the newbies (writing or using emulators) are
unwilling to
accept that and are instead making CGA palettes with dark yellow
instead of brown.
In my experience, dark yellow *is* brown. (At least as far as CRT
colours go.)
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2:45 p.m.
der Mouse wrote:
That doesn't help :-) For reference, see the chart here:
http://en.wikipedia.org/wiki/Color_Graphics_Adapter#The_CGA_color_palette
The color listed in that chart for "brown" is what I see on all 6 of my
CGA monitors and what I've remembered since 1983. The color listed as
"IBM 5153" is incorrect and that's what I'm trying to get history on so
that I can convince him otherwise.
I'm puzzled why people who have never seen the hardware are so driven to
make "factual" statements about it...?
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Want to help an ambitious games project? http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
[...]; the
newbies (writing or using emulators) are unwilling to
accept that and are instead making CGA palettes with dark yellow
instead of brown.
In my experience, dark yellow *is* brown. (At least as far as CRT
colours go.) 
2:43 p.m.
There is a bit of a spat going on in a few forums
regarding color index
#6 of IBM CGA. The old-timers know that it is brown from experience and
existing working hardware; the newbies (writing or using emulators) are
unwilling to accept that and are instead making CGA palettes with dark
yellow instead of brown.
Can anyone give me the history on why #6 is brown? Was it a design
mistake, or intentional? Is it a property of the monitor or something?
I can't find anything of substance to offer the newbies to convince them
otherwise; digital photos can be accused of being doctored or
miscalibrated (and yet is a digital photo showing "yellow" that started
this whole thing). About the only thing I can think of to offer as
proof is that the text colors in the VGA palette show brown, and IBM
wouldn't have done something like that by mistake -- or were they
perpetuating a mistake?
My recall of the color pallete in CGA mode was that the
"dark" versions of
the main colors were a bit flip from the main colors and that "brown"
really was "dark yellow." You could call it dark yellow all you wanted
(and some docs did) but once painted on the screen, it was brown. I think
white with the corresponding bit set (cleared?) was gray. Or was dark gray
equivalent to black...? I forget. I recall that something about it was
logically wierd and didn't make sense.
I have some docs at home I should dig through and see if I can find this.
Paper docs are much less subject to later revision than google searches...
-T
11:59 a.m.
My recall of the color pallete in CGA mode was that
the "dark" versions of
the main colors were a bit flip from the main colors and that "brown"
Correct in general, that bit corresponds to the I line to the monitor.
really was "dark yellow." You could call it
dark yellow all you wanted
(and some docs did) but once painted on the screen, it was brown. I think
white with the corresponding bit set (cleared?) was gray. Or was dark gray
equivalent to black...? I forget. I recall that something about it was
logically wierd and didn't make sense.
Well, colour 0 is black (all bits off). Colour 15 is light white (all
bits on). Colour 7 is either normal white or light grey (depending on
what you want to call it!). Colour 8 is grey in the IBM manuals, you
might think of it as light black. It actually does make sense if you look
at the hardware.
-tony
25 Jan
25 Jan
7:12 p.m.
I really shouldn't get involved in this at all, but I
do recall reading, probably in a review in PC Magazine
way back, that brown was was uncommon, whatever the h
that meant, until the EGA card came out, or something
to that effect. If people are seeing it though, then I
guess that's the way it is. I personally don't recall
seeing too much brown back then, and there certainly
wasn't any on my Tandy 2000.
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18 Jan
18 Jan
3:13 p.m.
I'm not sure if my previous message made it or not, so please ignore this if it
is a dupe.
If you look at IBM documentation (especially the BASIC manuals from the era) it
is clearly listed as Brown, not dark yellow.
End of discussion?
Yes, the lower numbered colors are just dimmer versions of the upper colors.
But it still looks brown to me if I fire up my PCjr, sitting right here next to
me. Perhaps the offending person should tone the brightness setting down?
They are getting sunburnt from having it up so high.
3:37 p.m.
mbbrutman-cctalk at brutman.com wrote:
If you look at IBM documentation (especially the BASIC
manuals from the era) it
is clearly listed as Brown, not dark yellow.
Is it possible for you to email me a scan of this? I'm not sure I have
anything official IBM that states that.
End of discussion?
With a scan, it would be :-)
Perhaps the offending person should tone the
brightness setting down?
Yes, but then that leaves things open to interpretation, and that's what
I'm trying to avoid (it was interpretation that led to the whole mess in
the first place).
Sorry if this seems like a silly issue to everyone, but the potential
for having the wrong colors in all 5150-style emulators is a big deal to me.
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Want to help an ambitious games project? http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
4:19 p.m.
On 1/18/2006 at 12:13 PM mbbrutman-cctalk at brutman.com wrote:
If you look at IBM documentation (especially the BASIC
manuals from the
era) it
is clearly listed as Brown, not dark yellow.
End of discussion?
The IBM CGA monitor displayed brown, not yellow. And dark yellow is NOT
brown. Give me a couple of hours and I'll research the matter in my O&A
manuals. But brown, not yellow.
Cheers,
Chuck
4:53 p.m.
On 1/18/2006 at 12:13 PM mbbrutman-cctalk at brutman.com wrote:
If you look at IBM documentation (especially the BASIC
manuals from the
era) it is clearly listed as Brown, not dark yellow.
Looks like the network around Q204/Q205 is the dark-yellow to brown
translation in the IBM CGA montor. I can scan that part of the circuit and
post it if anyone's interested.
I haven't checked, but wasn't there also special-casing in the EGA BIOS
code to handle the dark yellow=brown case?
Cheers,
Chuck
12:08 p.m.
On 1/18/2006 at 12:13 PM mbbrutman-cctalk at brutman.com wrote:
I wonder if we're looking at different schematics. In mine, Q204 and Q205
form the buffer stage for the Hsync signal. The emitter of Q205 seems to
be a blanking signal. the collector feeds sync to Q402 (the deflection
oscillator IC).
In mine, Q206 is the 'brwon kludge' I think.
If you look at IBM documentation (especially the
BASIC manuals from the
era) it is clearly listed as Brown, not dark yellow.
Looks like the network around Q204/Q205 is the dark-yellow to brown
translation in the IBM CGA montor. I can scan that part of the circuit and
post it if anyone's interested.
I haven't checked, but wasn't there also special-casing in the EGA BIOS
code to handle the dark yellow=brown case?
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.
-tony
8:56 p.m.
On 1/18/2006 at 5:08 PM ard at p850ug1.demon.co.uk wrote:
In mine, Q206 is the 'brwon kludge' I think.
Yup, slip of the neurons between looking at the schematic (with a binocular
loupe--silly thing is too small for my old eyes to read unaided) and
posting the email.
> I haven't checked, but wasn't there also
special-casing in the EGA BIOS
> code to handle the dark yellow=brown case?
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.
Ah, now you're going to make me look at the EGA BIOS listing too! Have you
no mercy? :) It seems to me that it was possible (in other EGA modes) to
display dark yellow instead of brown, but that the legacy CGA modes were
special-cased. I'll check on it, though.
Cheers,
Chuck
9:31 p.m.
On 1/18/2006 at 5:08 PM ard at p850ug1.demon.co.uk wrote:
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.
I'm not inclined to check the PGA BIOS, but the PGA display appears not to
do the color re-mapping.
Cheers,
Chuck
19 Jan
19 Jan
3:12 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
6:28 p.m.
On 1/19/2006 at 8:12 PM ard at p850ug1.demon.co.uk wrote:
IIRC the PGA monitor has analogue inputs, and does what
you'd expect.
Yup, it is indeed analogue.
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.
There was a PROM on the PGA, but it was for the onboard 8088. Probably no
BIOS per se. Probably the first shot in the "my graphics adapter has more
computational power than my motherboard" modern trend, although in the case
of the PGA, it was just an 8088 on the adapter, not anything fancier.
Cheers,
Chuck
7:13 p.m.
There was a PROM on the PGA, but it was for the onboard 8088. Probably no
BIOS per se. Probably the first shot in the "my graphics adapter has more
That's what I thought...
It was an odd device. IIRC in the high-res (better than CGA) mode, you
couldn't access the video memory directly. You had to send it commands
(draw a line, etc). Presumably it was not great for animations therefore...
It's still like to find one.
computational power than my motherboard" modern
trend, although in the case
of the PGA, it was just an 8088 on the adapter, not anything fancier.
Talking of peripherals with more power then their host, I'm currently
working on some old Epson laptops. The TF20 floppy drive is rather
overpowered fro the time. It could be used with the HX20, which had a
couple of 6301 processors and 16K RAM. The TF20, though, contains a Z80
and 64K RAM. About the same as the (CP/M) desktop computers of its time.
-tony
7:58 p.m.
In article <200601191528250129.0BB465E1 at 10.0.0.252>,
"Chuck Guzis" <cclist at sydex.com> writes:
There was a PROM on the PGA, but it was for the
onboard 8088. Probably no
BIOS per se. Probably the first shot in the "my graphics adapter has more
computational power than my motherboard" modern trend, although in the case
of the PGA, it was just an 8088 on the adapter, not anything fancier.
Someone donated me a CBM 8032 with an 8050 dual 5.25" floppy drive.
The floppy drive has twice the CPU horsepower of the main unit :-).
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18 Jan
18 Jan
5:23 p.m.
Chuck Guzis wrote:
Looks like the network around Q204/Q205 is the
dark-yellow to brown
translation in the IBM CGA montor. I can scan that part of the circuit and
post it if anyone's interested.
Please, it would be much appreciated! This would pretty much put to
rest this person's theory that CGA monitors only started doing "brown"
after EGA came out, which doesn't make any sense to me.
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Help our electronic games project: http://www.mobygames.com/
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6:05 p.m.
On 1/18/2006 at 4:23 PM Jim Leonard wrote:
Please, it would be much appreciated! This would
pretty much put to
rest this person's theory that CGA monitors only started doing "brown"
after EGA came out, which doesn't make any sense to me.
Okay, here's a grayscale tiff of the first of two pages (the second page
contains things like video drive and horizontal output). I leave the page
up for a day or so. I'dve scanned it as a monochrome image, but the shaded
part on the right side just wouldn't come out right.
http://www.sydex.com/photos/cgamon.tif
Cheers,
Chuck
6:37 p.m.
Got it, thank you!
Chuck Guzis wrote:
On 1/18/2006 at 4:23 PM Jim Leonard wrote:
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Help our electronic games project: http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
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Please, it would be much appreciated! This would
pretty much put to
rest this person's theory that CGA monitors only started doing "brown"
after EGA came out, which doesn't make any sense to me.
Okay, here's a grayscale tiff of the first of two pages (the second page
contains things like video drive and horizontal output). I leave the page
up for a day or so. I'dve scanned it as a monochrome image, but the shaded
part on the right side just wouldn't come out right.
http://www.sydex.com/photos/cgamon.tif
Cheers,
Chuck
19 Jan
19 Jan
7:54 p.m.
Chuck Guzis wrote:
Okay, here's a grayscale tiff of the first of two
pages (the second page
I hate to trouble you again, but now there is question from the
individual I am trying to convince that the sheet you scanned was from a
"later revision" of the tech ref. Can you scan the page with the
copyright date on it?
Was there a revised tech ref, or just one?
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Help our electronic games project: http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
A child borne of the home computer wars: http://trixter.wordpress.com/
8:12 p.m.
On 1/19/2006 at 6:54 PM Jim Leonard wrote:
Was there a revised tech ref, or just one?
No date--just a pub number of 6361470, no revision number. The O&A was a
"work in progress". Periodically, you were sent a bunch of looseleaf
3-ring sheets to add or exchange in the various sections. I discarded
nothing--just moved it to the back of each binder. There's only one CGA
display reference, and, as far as I can tell, no updates.
Cheers,
Chuck
9:12 p.m.
On 1/19/2006 at 6:54 PM Jim Leonard wrote:
>Was there a revised tech ref, or just one?
I should also mention that the schematic does NOT appear to be the work of
IBM. I suspect it was provided by the outfit IBM contracted to for the CGA
displays. Which is why I asked about a possible "Made in Korea" label.
Cheers,
Chuck
20 Jan
20 Jan
7:24 p.m.
Chuck Guzis wrote:
Oh for %deity's sake....
I will admit that the Techref I looked is a relatively late one in that I
bought it from IBM long after it was discontinued (they still had some in
stock). But I've never seen or heard of another version of the CGA
monitor
Chuck has posted the same information from his techref.
I feel it's unlikely IBM would have changed this (why do so?). And
rememebr the idea was perpetuated in the EGA card/monitor (why do this if
the earlier CGA card had not also done it?). And also I've seen clone CGA
monitors that had a circuit to perform the same function (often a 74138
decoder chip was used to detect clour 6). And we all know that some
clones missed out anything that was not strictly necessary
I feel the onus is on the original questioner to provide documentary
evidence, including schematics, showing an IBM CGA monitor that did not
do this. Or an example of an actual IBM-badged 5153 that does not
contain this circuitry. Should one be found I'll be happy to put a note
in my Techref. But until one is found I am happy to beleive that all
5153s include the brown-kludge.
-tony
Okay, here's a grayscale tiff of the first of
two pages (the second page
I hate to trouble you again, but now there is question from the
individual I am trying to convince that the sheet you scanned was from a
"later revision" of the tech ref. Can you scan the page with the
copyright date on it?
10:43 p.m.
Tony Duell wrote:
Oh for %deity's sake....
Believe me, I feel the same way. I'm just trying to convince a stubborn
person.
I feel the onus is on the original questioner to
provide documentary
He has digital photos of a 5153 that isn't performing the extra
conversion, which is what started this entire mess.
I believe the issue is settled with the person in question, so no need
to talk about it further. I provided the schematic along with your
explanation (credited to you) on http://www.oldskool.org/pc/cgacal and
that seems to have put the matter to rest.
Regardless, I'm not going to pursue it further (someone humorously
referred to me as "charging the CGA windmill" :-), although someday I
would like to know *why* IBM went through the trouble. Some engineer
has probably taken it to his grave.
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Help our electronic games project: http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
A child borne of the home computer wars: http://trixter.wordpress.com/
11:16 p.m.
Chuck Guzis wrote:
You know, if I turn the red gain down on a 5153, that
"brown" does indeed
come out dark yellow....
Yes, but that's not a user-accessible control, so I couldn't use that to
prove my point ("it's never been opened to be messed with", etc.).
I'm almost positive the 5153 photos that were used as "evidence" were
pictures of, let's face it, a slowly-failing 5153 or similar. I had to
ask for the schematic to prove my point.
Some people just believe what they want to believe. It was like a
religious argument at times.
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Help our electronic games project: http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
A child borne of the home computer wars: http://trixter.wordpress.com/
21 Jan
21 Jan
2:45 p.m.
Chuck Guzis wrote:
That depends on who the user is. I have certainly been inside my 5153.
You know, if I turn the red gain down on a 5153,
that "brown" does indeed
come out dark yellow....
Yes, but that's not a user-accessible control, so I couldn't use that to prove my point ("it's never been opened to be
messed with", etc.).
AFAIK there was no 'seal' on the 5153. It's hard to know if it's been
taken apart, therefore..
My first question is 'do all the other colours look _exactly_ right?'.
Obviously fidling with the drive controls would affect more than just the
brown clour.
I'm almost positive the 5153 photos that were used as "evidence" were
pictures of, let's face it, a slowly-failing 5153 or similar. I had to
Why 'slowly failing'? It's possible that one of the components in the
brown-kludge circuit has 'run down the curtain and joined the choir
invisible'... It's possible the fault, if there is one, just suddenly
appeared.
-tony
5:14 a.m.
Jim Leonard wrote:
Tony Duell wrote:
Dry joint at the base of Q206, obviously.
Gordon.
Oh for %deity's sake....
Believe me, I feel the same way. I'm just trying to convince a stubborn
person.
I feel the onus is on the original questioner to
provide documentary
He has digital photos of a 5153 that isn't performing the extra
conversion, which is what started this entire mess.
2:39 p.m.
Tony Duell wrote:
Oh come on. Photogrpahs are notoriously bad at preserving colours. And
although I don't have a digital camera, I've seen reference to white
balance adjustments on most (if not all) of them. Get that wrong and
brown could easily look yellow.
Heck, I am sure a bit of fiddling with GIMP or Photoshop or whatever
could do much the same thing.
Or of course his 5153 could have been tweaked (there are drive and cutoff
adjustments for the 3 guns, a bit less red gain (or a bit more green)
could make brown look like dark yellow (effectively undoing the effects
of that circuit). Or there could be a fault in that particular monitor
(maybe the transistor has failed or something.
Oh for %deity's sake....
Believe me, I feel the same way. I'm just trying to convince a stubborn
person.
I feel the onus is on the original questioner to
provide documentary
He has digital photos of a 5153 that isn't performing the extra
conversion, which is what started this entire mess. Regardless, I'm not going to pursue it further
(someone humorously
referred to me as "charging the CGA windmill" :-), although someday I
would like to know *why* IBM went through the trouble. Some engineer
has probably taken it to his grave.
Every year I give a little talk to HPCC (Handheld and Portable Computer
Club about the internals of one or more HP calculators/computers). Often,
after explaining some clever feature [1] I am asked 'why did HP do this'. To
which my reply is always the same : ' I can only tell you what's inside
the machine, not why it was put there. The former is deducable by taking
the thing apart and probing around. The latter needs access to the
designers'.
[1] An example is the beeper circuit on the 9830. It's a single
frequency, single duration beep. You give the circuit a pulse from the
I/O interface card, it gives a beep.
The 'extra' feature is a few extra components to give an amplitude
envelope to tbe output sound, just to make it sound a bit nicer. Well,
it _is_ an HP :-).
-tony
18 Jan
18 Jan
5:13 p.m.
It's in any of the classic IBM BASIC manuals that came with DOS 1.x through DOS
3.x. I'll scan the page for you if you don't have one. If you have the
manual, look up the COLOR command.
Other than that, the Wiki entry wasn't all that bad.
5:52 p.m.
mbbrutman-cctalk at brutman.com wrote:
It's in any of the classic IBM BASIC manuals that
came with DOS 1.x through DOS
3.x. I'll scan the page for you if you don't have one. If you have the
manual, look up the COLOR command.
I'll check for this and email you privately if I need it.
Other than that, the Wiki entry wasn't all that
bad.
It had better be, I wrote more than half of it :-)
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Help our electronic games project: http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
A child borne of the home computer wars: http://trixter.wordpress.com/
4:10 p.m.
Brown was really brown on an IBM display anyway. It wasn't just a
darker color as other people had suggested. The cheaper rip off
monitors typically did not do "true" IBM brown. Why IBM made this a
design requirement, I have no idea. If I have time, I will analyze
the IBM color CGA monitor schematics I have. IBM went to a LOT of
trouble to combine signals for I, B, at 0 and R and G at 1 to get Brown.
I At 02:03 PM 1/18/2006, Jim Leonard wrote:
There is a bit of a spat going on in a few forums
regarding color
index #6 of IBM CGA. The old-timers know that it is brown from
experience and existing working hardware; the newbies (writing or
using emulators) are unwilling to accept that and are instead making
CGA palettes with dark yellow instead of brown.
Can anyone give me the history on why #6 is brown? Was it a design
mistake, or intentional? Is it a property of the monitor or something?
I can't find anything of substance to offer the newbies to convince
them otherwise; digital photos can be accused of being doctored or
miscalibrated (and yet is a digital photo showing "yellow" that
started this whole thing). About the only thing I can think of to
offer as proof is that the text colors in the VGA palette show
brown, and IBM wouldn't have done something like that by mistake --
or were they perpetuating a mistake?
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Want to help an ambitious games project? http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
12:04 p.m.
Brown was really brown on an IBM display anyway. It wasn't just a
darker color as other people had suggested. The cheaper rip off
monitors typically did not do "true" IBM brown. Why IBM made this a
design requirement, I have no idea. If I have time, I will analyze
Correct. One thoguht : There is nothing I can see that particularly
detects colour 6 in the NTSC encoder on the CGA card itself. So, what
does a composite monitor display for colour 6? Dark Yellow, or Brown? Was
the mod to the 5153 monitor done to make it agree with the display on a
compositie monitor?
the IBM color CGA monitor schematics I have. IBM went
to a LOT of
trouble to combine signals for I, B, at 0 and R and G at 1 to get Brown.
For 'LOT of trouble', read : 4 open-collector NOT gates (but 2 '05s were
needed anyway to provide 8 gates to buffer the signals), 1 transistor,
and a handful of passives.
-tony
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