• Please review our updated Terms and Rules here

what is composite CGA?

oblivion

Veteran Member
Joined
Aug 28, 2010
Messages
981
Location
Scottsdale, AZ
so my previous understanding of a CGA video card was you had 2 options, you could output via the digital DE-9 for CGA, Hercules and all the other modes that use the CGA standard and then you had your RCA jack for outputting color composite via the analog cable to a TV with a composite jack.

I'm told though that you can also output color or mono composite signal via the DE-9 to a CGA monitor which is called composite CGA. can anyone elaborate on this? does this mean one can output a composite color signal to a CGA monitor that lacks a RCA input for games that support it? whenever I try this I just get a monochrome image which I first assumed was Hercules mode.
 

Chuck(G)

25k Member
Joined
Jan 11, 2007
Messages
39,715
Location
Pacific Northwest, USA
Composite video, which is usually referred to as CVBS combines sync, chroma and luma information into a single analog signal. Early cards, like the CGA, fudge the signal encoding somewhat, but it passes muster for most TV equipment.

Converting-single-ended-video-to-differential-video-_image1-1349301494.PNG


Hercules is not an option, as the horizontal sync frequency doesn't match any NTSC or PAL standard.
 

2icebitn

Banned
Joined
Sep 22, 2017
Messages
1,861
Location
Principality of Xeon
A CGA monitor accepts 6 seperate inputs, red, green, blue, intensity, vertical retrace and horizontal retrace. These 6 signals are combined, however sloppily, into 1 signal, known as an RS-170 composite signal. This is a carrier less signal that can't directly be input to a traditional television, you need an rf modulator to impose the composite signal onto a channel 2 or 3 carrier signal, whatever frequencies they are. A composite signal can directly accept an RS-170 ( or NTSC ) composite signal. But an RGBI monitor ( CGA is an example) or any analog RGB monitor, like a Mulyisync, cannot. A multisync can accept input from a CGA card if set to receive ttl inputs. To accept a VGA signal, it has to be set to analog.
 

Chuck(G)

25k Member
Joined
Jan 11, 2007
Messages
39,715
Location
Pacific Northwest, USA
My "traditional TV" has jacks for video and audio. It's what my ATSC converter box feeds. Video and audio jacks have been standard fare for quite some time now.
 

SomeGuy

Veteran Member
Joined
Jan 2, 2013
Messages
4,203
Location
Marietta, GA
*some* CGA clone cards omit the RCA connector and instead output that signal on one of the normally unused pins on the DB9 RGB connector. That way manufacturers could fit a parallel port or something on the card and still give users the option to use composite with the addition of a simple plug adapter.
 

Trixter

Veteran Member
Joined
Aug 31, 2006
Messages
7,259
Location
Chicagoland, Illinois, USA
so my previous understanding of a CGA video card was you had 2 options, you could output via the digital DE-9 for CGA, Hercules and all the other modes that use the CGA standard and then you had your RCA jack for outputting color composite via the analog cable to a TV with a composite jack.

Yes, if a CGA card has an RCA jack, that outputs a composite signal. (EGA cards with RCA jacks mostly do not, as those are feature connector jacks and not video output jacks.)

I'm told though that you can also output color or mono composite signal via the DE-9 to a CGA monitor which is called composite CGA.

No, the CGA RGB TTL port does not contain the composite output signal. TTL is a digital signal, and each R, G, B, and I pin only accepts ON or OFF. None of them are analog, and no other pin carries an analog/composite signal.
 

MikeS

Veteran Member
Joined
Dec 23, 2005
Messages
7,493
Location
Toronto ON Canada
...I'm told though that you can also output color or mono composite signal via the DE-9 to a CGA monitor which is called composite CGA. can anyone elaborate on this? does this mean one can output a composite color signal to a CGA monitor that lacks a RCA input for games that support it? whenever I try this I just get a monochrome image which I first assumed was Hercules mode.
Are you sure you're using the right terminology? CGA is CGA; there really isn't "composite CGA", it is composite video AKA RS170, NTSC in North America.

CGA monitors indeed generally have a DE-9 CGA input and no RCA input, so how exactly are you connecting a composite signal (RCA plug) to a CGA monitor which lacks an RCA input?

Not to be pedantic, but to use a composite monitor or TV/VCR etc. with a composite input (usually the yellow connector) you would use a shielded RCA-RCA coax cable connected to the CGA card's composite output.

As mentioned above, a few non-standard CGA cards used an unused pin on the DE-9 to output composite (analog) video, but this is unusual; it can also be risky because some cards also output 12V on an unused pin...

Note that whether you get colour on the composite output depends on the MODE selected in software.

Some reading:
https://www.seasip.info/VintagePC/cga.html

m
 

Chuck(G)

25k Member
Joined
Jan 11, 2007
Messages
39,715
Location
Pacific Northwest, USA
Back in the day, I just tapped into the video IF section of my (all tube) Zenith B&W. But I had a 70s transistor Sony with both video (SO239) input as well as a standard RF tuner. Really, RCA connectors were best suited for audio.
 

oblivion

Veteran Member
Joined
Aug 28, 2010
Messages
981
Location
Scottsdale, AZ
Are you sure you're using the right terminology? CGA is CGA; there really isn't "composite CGA", it is composite video AKA RS170, NTSC in North America.

CGA monitors indeed generally have a DE-9 CGA input and no RCA input, so how exactly are you connecting a composite signal (RCA plug) to a CGA monitor which lacks an RCA input?

Not to be pedantic, but to use a composite monitor or TV/VCR etc. with a composite input (usually the yellow connector) you would use a shielded RCA-RCA coax cable connected to the CGA card's composite output.

As mentioned above, a few non-standard CGA cards used an unused pin on the DE-9 to output composite (analog) video, but this is unusual; it can also be risky because some cards also output 12V on an unused pin...

Note that whether you get colour on the composite output depends on the MODE selected in software.

Some reading:
https://www.seasip.info/VintagePC/cga.html

m

It's what I was told I was getting on my image, I never even heard of composite RGB before and that's why i'm asking.

I'll give an example. I have an old 8088 with a ATI small wonder card installed. It is currently connected to a Tandy CM-4 RGB monitor via the DE-9 connector. when I play a game like Burger Time or Leisure Suit Larry I get a monochrome image. I'm not an expert on CGA so I just assumed it was defaulting to Hercules mode and that LSL had no CGA color mode. Someone else told me it was not Herc mode but monochrome "composite CGA" mode.

note if I select RGB monitor in Burger Time setup options I get CGA color and if I select "color" from the upper menu in LSL I get color (hideous color). I should also note that if I say, connect the card via the RCA jack to a TV with a composite jack I only get a b/w monochrome image regardless on how I set the switches on the CGA card and regardless if the game in question supports color composite mode. For instance Burger Time will only display in B/W via the RCA jack over a composite cable.

so basically i'm just trying to figure out what i'm seeing and what the correct terminologies are.
 

VileR

Veteran Member
Joined
Jul 21, 2011
Messages
579
Location
Israel
whenever I try this I just get a monochrome image which I first assumed was Hercules mode.
You're seeing the RGBI representation of images that are *meant* to be output as composite over the RCA jack. Typically, if you did that you'd get color- over NTSC the high-frequency luma detail in such an image would be decoded as chroma (if a color burst is present) and displayed as artifact colors. Perhaps non-intuitively, most games/software that exploited this settled on using the CGA's 640x200 mode w/black and white as the two colors, since it actually yields a very useful artifact color 'palette'.

So "composite CGA mode" just seems to be a commonly(?) used term for 640x200 (mode 6) with the color burst enabled, because it was widely used for this purpose, although it's inaccurate (composite describes the signal, not the 'mode') and confusing (other CGA modes can be used just fine over composite, and in color too).
 
Last edited:

oblivion

Veteran Member
Joined
Aug 28, 2010
Messages
981
Location
Scottsdale, AZ
You're seeing the RGBI representation of images that are *meant* to be output as composite over the RCA jack. Typically, if you did that you'd get color- over NTSC the high-frequency luma detail in such an image would be decoded as chroma (if a color burst is present) and displayed as artifact colors. Perhaps non-intuitively, most games/software that exploited this settled on using the CGA's 640x200 mode w/black and white as the two colors, since it actually yields a very useful artifact color 'palette'.

That must be why you're seeing a monochrome image on RGBI; naturally no CGA-only monitor would sync to a Hercules signal.

alright, starting to make sence a little better. just to clarify.

so Hercules mode should only kick in if I'm using a monochrome only monitor correct?

any idea why when I hook things up via the RCA jack to a color composite monitor I only get B/W? Ive tried 2 different CGA cards and I get the same issue. I double checked the switches on the motherboard and the cards to make sure they were set to accept color modes. I read online one guy had a similar issue and he adjusted a variable resistor on the motherboard and got color but my board doesn't seem to have anything like that.
 

SomeGuy

Veteran Member
Joined
Jan 2, 2013
Messages
4,203
Location
Marietta, GA
No, Hercules mode is only available if you are using a Hercules monographics adapter card or Herc clone, not a CGA card.

Hercules cards must be used with a monographics or IBM MDA compatible monitor.

"Hercules" is a clone of the IBM MDA (text only) card that adds graphics capabilities using the same MDA monitors. It was a popular upgrade for MDA users, and herc clone cards were used in cheap PC clones as MDA monitors were less expensive than color.

Many CGA cards disable color when displaying text modes via composite. Otherwise it would be unreadable. Try some graphics modes instead.
 

2icebitn

Banned
Joined
Sep 22, 2017
Messages
1,861
Location
Principality of Xeon
If by Hercules mode you mean MDA monochrome (I'm not really clear what you're asking), no usually your card, if it supports it, has to be setup via dip switches to output that video. Unless the card can sense what type of monitor it's connected to ... astronomically unlikely. VGA monitors/cables have sense pins that the card tests. But don't think there are any CGA/MDA/? era cards that do that. Someone may chime in I have a feeling though ...
 

oblivion

Veteran Member
Joined
Aug 28, 2010
Messages
981
Location
Scottsdale, AZ
No, Hercules mode is only available if you are using a Hercules monographics adapter card or Herc clone, not a CGA card.

Hercules cards must be used with a monographics or IBM MDA compatible monitor.

"Hercules" is a clone of the IBM MDA (text only) card that adds graphics capabilities using the same MDA monitors. It was a popular upgrade for MDA users, and herc clone cards were used in cheap PC clones as MDA monitors were less expensive than color.

Many CGA cards disable color when displaying text modes via composite. Otherwise it would be unreadable. Try some graphics modes instead.


The card is a ATI Small Wonder CGA card but it also supports Hercules graphics mode
 

trr94001

Member
Joined
Jan 9, 2014
Messages
33
Location
Connecticut
That was me on YouTube the other day. Sorry if I wasn’t very clear. VileR is entirely correct. There are no explicit software modes for CGA’s composite output but clever programmers could exploit composite artifacting to generate more colors. Some games like Ultima 2 did this by simply anticipating the alternate/additional colors you’d see when viewing 4 color 320x200 graphics but you could also go all out by using 640x200 mono to generate pure Apple II style pseudocolors.

As for your ATI card, I suspect there’s something wrong with the composite output, probably the colorburst is weak or absent entirely.
 

kgober

Veteran Member
Joined
Mar 19, 2017
Messages
617
Location
New Jersey, USA
In my experience cheap clone CGA cards did not support whatever it was that was needed to get color composite output -- it always appeared black and white.

But the CGA card on a Compaq portable (and on real IBM PCs, presumably) did support color output and there were indeed games that looked better this way than they did using RGBI (e.g. Starflight).

I don't know if the ATI Small Wonder card supports color composite or not.
 

SomeGuy

Veteran Member
Joined
Jan 2, 2013
Messages
4,203
Location
Marietta, GA
The ATI Small Wonder is a very unique video card. It is not a common CGA, Herc, or switchable clone CGA/Herc card.

Apparently it does support emulating Hercules graphics modes with an RGBI monitor via video interlacing. It also supports extended RGB modes compatible with Plantronics video cards (320x200x16 and 640x200x4)

There is a detailed thread about it here: http://www.vcfed.org/forum/showthread.php?17357-ATI-Small-Wonder-Graphics-Solution-v1

It sort of sounds like one would set the jumpers and motherboard to Herc or MDA, but set the video cards monitor selection jumper to RGBI/Composite. If it were possible to switch modes using software, I would expect this would only be possible using software utilites bundled with the card.
 

MikeS

Veteran Member
Joined
Dec 23, 2005
Messages
7,493
Location
Toronto ON Canada
The ATI Small Wonder is a very unique video card. It is not a common CGA, Herc, or switchable clone CGA/Herc card.
...
Yeah, he could have mentioned earlier that it's an ATI SW/GS (and the version number), not, strictly speaking, a CGA card; would have saved some time and confusion.. ;-)
 
Top