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First post, by awgamer

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Or is that a CGA card limitation? What I'm getting at is if a CGA card were upgraded with enough memory and palette control would a CGA monitor display whatever it's told? Also curious if a CGA monitor could be driven to do 240 scan lines.

Reply 1 of 20, by 133MHz

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CGA is 4-bit digital video (3-bit RGB + 1-bit intensity) which gives 2^4 = 16 possible colors. Unlike analog you're stuck with those.
Video timings are very close to SDTV so you could do 262 (~240 active) vertical lines, even 312 (~288 active) by dropping the frame rate to 50Hz.

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Reply 2 of 20, by awgamer

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OK, so only 16 colors, but what about the CGA palette, is that hard wired by the monitor as well? An aside, seeing as how composite wasn't widely accepted, it's a shame plantronics didn't catch on and overtake CGA as THE early PC standard in 82, doing 320x200 16 colors it would have been matching competitors.

Reply 4 of 20, by VileR

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awgamer wrote:

OK, so only 16 colors, but what about the CGA palette, is that hard wired by the monitor as well?

It's a direct consequence of how the digital RGBI color model works. The only thing hardwired into the monitor is specific circuitry to make color 6 brown, i.e. RGB {2/3, 1/3, 0}. Otherwise it would be "dark yellow", a color also affectionately known as "Ski Free Dog Pee".

An aside, seeing as how composite wasn't widely accepted, it's a shame plantronics didn't catch on and overtake CGA as THE early PC standard in 82, doing 320x200 16 colors it would have been matching competitors.

Plantronics was just one of many 3rd-party "super CGA" extensions at the time and even IBM's own attempt with the PCjr didn't prove enticing enough for the masses. The Tandy 1000 pretty much did what you suggest though.

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Reply 6 of 20, by Anonymous Coward

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There may be other tricks to get more than 16 colours on CGA. Check this out: http://www.vintage-computer.com/vcforum/showt … 4k-Mode-Preview

I am pretty sure he is using a TTL display and not composite mode.

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Reply 7 of 20, by VileR

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Anonymous Coward wrote:

There may be other tricks to get more than 16 colours on CGA. Check this out: http://www.vintage-computer.com/vcforum/showt … 4k-Mode-Preview

I am pretty sure he is using a TTL display and not composite mode.

He is - but that's a combination of dithering and flickering. Which I *think* is also how some clone CGA cards were able to get 16 shades of green on the TTL-only 5151.

awgamer wrote:

Yeah, but plantronics came out in 82, while jr and tandy were late in 84.

There was a PC card with 1024x1024 16-color graphics in 1982, too. Now that's a little bit more impressive than the Plantronics ;)

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Reply 8 of 20, by awgamer

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Sure but the 'what if' I'm going on about is something that should have been the standard instead of the mistake that was CGA, not a high priced niche. IBM's argument about saving money for some, two 8k ram chips was $70 back then, they should have put in two sockets for the option to upgrade to do 320x200 16c on the crt, it totally fits the upgrade nature of the pc, but obviously they didn't do that.

Reply 12 of 20, by idspispopd

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EGA monitors are still digital but have 6 bits of input so they support 64 colors - of which an EGA card can only display 16 at the same time, and only when the it displays a 640x350 resolution. At 320x200 or 640x200 2 bits are ignored so the display is still locked to 16 colors to ensure compatibility to CGA monitors.

Reply 13 of 20, by VileR

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awgamer wrote:

Sure but the 'what if' I'm going on about is something that should have been the standard instead of the mistake that was CGA, not a high priced niche.

List price for the Plantronics Colorplus was $995 in 1982... still not exactly priced for the home consumer. (BTW, the M197 thing mentioned right next to it is one of those other "super-CGA" solutions I was referring to.)

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Reply 14 of 20, by awgamer

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Back then list prices where higher than sales. In June 83, plantronics was selling for $475, $379 in November. I imagine the 640x400 & 320x400 modes of the M197 were achieved with interlacing if using CGA monitors. If that's the case, interesting to learn CGA monitors can handle 400 interlaced, the flickering from 60 Hz interlaced must have been brutal, or do CGA phophors last longer?

Last edited by awgamer on 2014-07-29, 21:04. Edited 1 time in total.

Reply 15 of 20, by Great Hierophant

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I believe that some monitors that used the 9-pin TTL RGB connector before the IBM PC 5153 Color Monitor may have only supported eight colors, ignoring the intensity signal, or used dark yellow instead of brown for color #6.

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Reply 16 of 20, by VileR

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Great Hierophant wrote:

I believe that some monitors that used the 9-pin TTL RGB connector before the IBM PC 5153 Color Monitor may have only supported eight colors, ignoring the intensity signal, or used dark yellow instead of brown for color #6.

If you look through the magazines circa 1982, many RGB monitors (Sony, Amdek) were sold along with "intensity modifications for 16-color capability", and there was also the Princeton HX-12 which closely matched the IBM look and had 16-color support built in.
But yeah, I'd be very surprised if any of them had a brown #6. In the HX-12 photo it actually looks very yellow.

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Reply 18 of 20, by 133MHz

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'CGA' in the arcade world refers to the video scan rate which is 15kHz horizontal and 50~60Hz vertical, which is also known as 'Standard Resolution'. That said arcade monitors take analog RGB and TTL level sync, but in most cases the RGB voltage levels are not directly compatible with RGB SCART or VGA signaling. In short they're simplified TVs without tuner/IF, chroma or audio, just a bare RGB + sync input.

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Reply 19 of 20, by subhuman@xgtx

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133MHz wrote:

'CGA' in the arcade world refers to the video scan rate which is 15kHz horizontal and 50~60Hz vertical, which is also known as 'Standard Resolution'. That said arcade monitors take analog RGB and TTL level sync, but in most cases the RGB voltage levels are not directly compatible with RGB SCART or VGA signaling. In short they're simplified TVs without tuner/IF, chroma or audio, just a bare RGB + sync input.

I was curious about that, thanks for the info.

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