More on CGA
10 messages · 2008-02-29 → 2008-03-03 · Yahoo Group era · View archive on archive.org
Participants: Fred, Adam Trionfo, William McBrine, Robert "Exile In Paradise" Murphey, Glen Goodwin
Preserved from the Timex/Sinclair 2068 Yahoo Group (2001–2019), which is no longer online. Text reproduced from the archive.org archive; email addresses masked.
Messages
1. More on CGA
Adam Trionfo · Fri, 29 Feb 2008 16:42
I remember using the CGA monitor with a PC that I had in about 1989 or 1990. I recall the letters being not as fine when compared to an EGA or monochrome monitor. Thinking about this now, I guess it would have to be because of the dot pitch. I've searched using Google and I have been unable to find the dot-pitch of CGA monitors. Were some better than others (just like today), or was there a "standard." I'd guess, from memory, that the monitor that I used must have been .39 or maybe even .42 dot pitch. Does this sound about right? Whatever the dot-pitch is, it would still give a clear picture. Check out this really good example of composite from a CGA IBM adapter and CGA monitor vs. the TTL RGB mode. The difference is quite incredible!
http://en.wikipedia.org/wiki/Image:CGA_CompVsRGB_Text.png
Lastly, I guess that the IBM CGA adapter must have used the exact 16 colors (well, 8 colors plus intensity) that the T/S 2068 used. Right?
Adam
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2. Re: [ts2068] More on CGA
Fred · Sat, 1 Mar 2008 14:06:
On 01/03/2008, at 11:42, Adam Trionfo wrote:
> Lastly, I guess that the IBM CGA adapter must have used the exact 16
> colors (well, 8 colors plus intensity) that the T/S 2068 used. Right?
Nope, two distinct palettes (the brown would have come in handy on the
TS).
Fred
3. RE: More on CGA
Adam Trionfo · Fri, 29 Feb 2008 19:54
Fred wrote:
>>
Nope, two distinct palettes [for the IBM CGA adapter] (the brown would
have come in handy on the TS).
>>
Wait a second. Let me get this straigt. If a CGA monitor is hooked up to
a T/S 2068, you'll have a nice clear picture, but the wrong colors? Am I
missing something here?
Adam
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4. Re: [ts2068] RE: More on CGA
Fred · Sat, 1 Mar 2008 18:43:
On 01/03/2008, at 14:54, Adam Trionfo wrote:
> Fred wrote:
>>> Nope, two distinct palettes [for the IBM CGA adapter] (the brown
>>> would
>>> have come in handy on the TS).
> Wait a second. Let me get this straigt. If a CGA monitor is hooked
> up to
> a T/S 2068, you'll have a nice clear picture, but the wrong colors?
> Am I
> missing something here?
Yes, you are missing something :)
CGA monitors do not show a fixed palette of 16 colours, they can show
the full gamut of colours. The limitation is in the hardware that
generates the video signal.
When the TS feeds it you see the expected colours.
Fred
5. Re: [ts2068] RE: More on CGA
William McBrine · Sat, 1 Mar 2008 07:25:
On Sat, 1 Mar 2008, Fred wrote:
> CGA monitors do not show a fixed palette of 16 colours, they can show
> the full gamut of colours. The limitation is in the hardware that
> generates the video signal.
I believe you're mistaken.
--
William McBrine <[email]>
6. Re: [ts2068] RE: More on CGA
Robert "Exile In Paradise" Murphey · Sat, 01 Mar 2008 13:36
On Sat, 2008-03-01 at 07:25 -0500, William McBrine wrote:
> On Sat, 1 Mar 2008, Fred wrote:
>
> > CGA monitors do not show a fixed palette of 16 colours, they can
> show
> > the full gamut of colours. The limitation is in the hardware that
> > generates the video signal.
>
> I believe you're mistaken.
"CGA monitors used four digital signals to control
the three electron guns used in color CRTs, in a
signalling method known as RGBI, or Red Green and
Blue, plus Intensity. Each of the three RGB colors
can be switched on or off independently. The
intensity bit increases the brightness of all guns
that are switched on, or if no colors are switched
on the intensity bit will switch on all guns at a
very low brightness to produce a dark grey. A CGA
monitor is only capable of rendering 16 colors. The
CGA monitor was not exclusively used by PC based
hardware. The Commodore 128 could also utilize CGA
monitors. Many CGA monitors were capable of displaying
composite video via a separate jack.
EGA monitors used six digital signals to control
the three electron guns in a signalling method
known as RrGgBb. Unlike CGA, each gun is allocated
its own intensity bit. This allowed each of the
three primary colors to have four different states
(off, soft, medium, and bright) resulting in 64
colors."
-- http://en.wikipedia.org/wiki/Computer_display
--
Robert "Exile In Paradise" Murphey
How come financial advisors never seem to be as
wealthy as they claim they'll make you?
7. Re: [ts2068] RE: More on CGA
Fred · Sun, 2 Mar 2008 12:11:
On 02/03/2008, at 6:36, Robert Exile In Paradise Murphey wrote:
> On Sat, 2008-03-01 at 07:25 -0500, William McBrine wrote:
>> On Sat, 1 Mar 2008, Fred wrote:
>>
>>> CGA monitors do not show a fixed palette of 16 colours, they can
>> show
>>> the full gamut of colours. The limitation is in the hardware that
>>> generates the video signal.
>>
>> I believe you're mistaken.
Well colour me corrected! Thanks for the information.
I always thought they were analogue RGB - double-checking now shows
that the TS has TTL outputs available, not analogue in any case.
Apologies for the misinformation!
I am not sure what colours output you get with a TS connected to a CGA
monitor then - does anyone have any screenshots? I presume you would
lose the BRIGHT colours using this type of connection?
Fred
8. Re: [ts2068] RE: More on CGA
William McBrine · Sat, 1 Mar 2008 22:43:
On Sun, 2 Mar 2008, Fred wrote:
> I presume you would lose the BRIGHT colours using this type of
> connection?
I don't see why -- that's what the CGA "Intensity" line is for. However,
ISTR reading about at least one 2068 RGB interface that did lose BRIGHT.
--
William McBrine <[email]>
9. Re: [ts2068] RE: More on CGA
Fred · Sun, 2 Mar 2008 16:42:
On 02/03/2008, at 14:43, William McBrine wrote:
> On Sun, 2 Mar 2008, Fred wrote:
>> I presume you would lose the BRIGHT colours using this type of
>> connection?
>
> I don't see why -- that's what the CGA "Intensity" line is for.
> However,
> ISTR reading about at least one 2068 RGB interface that did lose
> BRIGHT.
I just suspect this as I don't see any intensity signal at the TS2068
edge connector (just TTL RGB) and I have also read about RGB monitor
interfaces that lose BRIGHT back in the day?
I am also confused that the quote from wikipedia given by Robert says
"A CGA
monitor is only capable of rendering 16 colors" as each of RGB can
only be switched on or off independently + the intensity line, but
Wikipedia's Color_Graphics_Adaptor article has brown being the low
intensity red and green with an inconsistently low level of green in
the signal.
Does this mean that a TS connected to a CGA monitor produces brown
instead of non-bright yellow? <http://www.oldskool.org/pc/cgacal/>
suggests that the answer is yes and it is circuitry in the monitor
itself that does the adjustment!
One other option that may exist for a high-quality video output from
the TS is the SCLD seems to have Y U V output fed into the modulator
for creating composite/RF video, does anyone know if these Y U V
signals are likely to be compatible with modern component video inputs?
Fred
10. Re: [ts2068] RE: More on CGA
Glen Goodwin · Mon, 03 Mar 2008 15:45
Fred wrote:
> Does this mean that a TS connected to a CGA monitor produces brown
> instead of non-bright yellow? <http://www.oldskool.org/pc/cgacal/>
> suggests that the answer is yes and it is circuitry in the monitor
> itself that does the adjustment!
If Jim Leonard (perpetrator of www.oldskool.org) says it, you
can believe it. He has done an incredible amount of research into
the older PC-type monitors.
If I recall correctly, IBM made an error in the brown/yellow
output on the CGA video cards and then had to kludge the monitors
to compensate. But Jim would know for sure.
Glen
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