CGA mystery

[sombunall]

In my lab in high school we had original IBM XTs. When we ran "ibasic.com" or "cbasic.com" on them we could then use the command "screen 1" to change to graphics mode. The graphics was CGA but the monitor was monochrome. It was not herculese graphics I don't think. How is this possible? Did IBM sell monochrome monitors that plug into CGA? I never seen such a monitor so I don't know if it exists.

 

[vwestlife]

It was most likely a monochrome composite monitor. IBM itself never sold one for the PC*, but almost every personal computer in the 1980s used composite video so aftermarket ones were extremely popular.

*IBM did sell a small mono composite monitor to go along with the PC Convertible laptop, and the Portable PC had a 9-inch mono composite monitor built-in.

 

[MikeS]

It was most likely a monochrome composite monitor. IBM itself never sold one for the PC*, but almost every personal computer in the 1980s used composite video so aftermarket ones were extremely popular.

*IBM did sell a small mono composite monitor to go along with the PC Convertible laptop, and the Portable PC had a 9-inch mono composite monitor built-in.

Maybe IBM didn't make one, but there certainly were monochrome CGA (9-pin) monitors as well as dual-mode MGA/CGA monochrome monitors; I've got some.

 

[sombunall]

It was most likely a monochrome composite monitor. IBM itself never sold one for the PC*, but almost every personal computer in the 1980s used composite video so aftermarket ones were extremely popular.

*IBM did sell a small mono composite monitor to go along with the PC Convertible laptop, and the Portable PC had a 9-inch mono composite monitor built-in.

It's funny I swore I saw the IBM logo on them. They even look like the ones in the pictures too.

 

[vwestlife]

It's funny I swore I saw the IBM logo on them. They even look like the ones in the pictures too.

In the 640x200 CGA graphics mode (SCREEN 2) the display is black-and-white even on a color monitor. Maybe you're thinking of that?

If these were true monochrome monitors (not color monitors displaying monochrome graphics), then what color was the CRT phosphor: green, or amber (yellowish-orange)? The original IBM monochrome monitor (5151) has green phosphor and has no power switch (it switches on and off along with the computer).

 

[Chuck(G)]

IBM made monitors that looked very similar to the 5151. For example here's the 00-1 monitor for the Displaywriter. It has a filter installed over the screen; without it, it looks nearly identical to the 5151. Similar monochrome monitors were also made for POS and industrial use.

 

[sombunall]

When you did screen 1 I think it was 320x200x4. It was a green phosphor and looked just like that attachment. The 4 colors were just different shades of green.

Just now I plugged an STB The Chauffeur card into the XT and I was able to get CGA resolution using PC Magazine's setmode.com on a monochrome monitor!

 

[sombunall]

...and now a pic of the rare STB The Chauffeur CGA monochrome card! Ok maybe it's not rare. I don't know.

 

[per]

...and now a pic of the rare STB The Chauffeur CGA monochrome card! Ok maybe it's not rare. I don't know.

Quite some cards could do CGA graphics on a monochrome monitor. Some (like the ATI Small Wonder Graphics Solution) could even do plantonics color+ graphics on monochrome monitors, but very few titles actually takes use of plantonics. The ATI SWGS could even do all CGA modes in 16-colours!

But note one thing. The card problably uses MGA, which is just close enough to CGA to be compatible with most titles. That is, the sync rates are the same as the MDA, and the MDA 9*14 character font will problably be used in textmode instead of the 8x8 CGA font. In addition, some CGA registers won't work as normal.

 

[vwestlife]

...and now a pic of the rare STB The Chauffeur CGA monochrome card! Ok maybe it's not rare. I don't know.

That is an MDA/Hercules-type card that emulates CGA graphics on a standard IBM 5151 monochrome monitor. There is an ad for it on page 11 of this interesting newsletter from 1986:

http://sp.ntpcug.org/Newsletters/NTPCUG - 1986-03.pdf

It claims "colors appear in 16 shades of gray," but they probably mean 16 different shades of cross-hatching (similar to a vintage black & white Macintosh), because MDA only provides high intensity and normal intensity, not shades of gray (or green, or whatever phosphor color your monitor is).

They could also conceivably flicker the pixels on and off at various seizure-inducing rates in order to simulate grayscales, as early laptop monochrome LCD panels did, but that probably wouldn't show up well on an IBM 5151 anyway due to its very long-persistence "radar scope" phosphor.

 

[Marrr]

...and now a pic of the rare STB The Chauffeur CGA monochrome card! Ok maybe it's not rare. I don't know.

I can see "MONITOR TYPE" DIP-switch there, so I guess it supports color monitors too, doesn't it?

 

[per]

They could also conceivably flicker the pixels on and off at various seizure-inducing rates in order to simulate grayscales, as early laptop monochrome LCD panels did, but that probably wouldn't show up well on an IBM 5151 anyway due to its very long-persistence "radar scope" phosphor.

In fact, due to the long-persistence phosphor, it does if fact show up well on the IBM 5151... unless the develpers of the card really missed out on the timing cirquits. The ATI SWGS shows up perfectly with 16 actual shades of green on my IBM 5151, and visually it doesn't even flicker!

 

[sombunall]

In fact, due to the long-persistence phosphor, it does if fact show up well on the IBM 5151... unless the develpers of the card really missed out on the timing cirquits. The ATI SWGS shows up perfectly with 16 actual shades of green on my IBM 5151, and visually it doesn't even flicker!

Do you think I could get that with my Chauffeur? What program do you use? I don't know much about CGA because I never actually saw a CGA card plugged into a CGA color monitor before since I only used it in my high school lab.

 

[per]

Do you think I could get that with my Chauffeur? What program do you use? I don't know much about CGA because I never actually saw a CGA card plugged into a CGA color monitor before since I only used it in my high school lab.

Standard MGA (CGA-emulation on a mono. monitor) is almost the same as CGA with shades of green. That is, in textmode you should get 16 colors, in graphics mode you should at least get 4 (med-res) or 2 (high-res) colors.

Whereof your card supports more colors depends on if it supports emulation of other adapters that got more colors. One way to check is if you got a diagnostics disk that followed that particular card, or if you got the manual. Anyways, most games use the standard 4-color med-res mode so it's not too critical if your card doesn't support more than standard MGA/CGA.

 

[sombunall]

Standard MGA (CGA-emulation on a mono. monitor) is almost the same as CGA with shades of green. That is, in textmode you should get 16 colors, in graphics mode you should at least get 4 (med-res) or 2 (high-res) colors.

Whereof your card supports more colors depends on if it supports emulation of other adapters that got more colors. One way to check is if you got a diagnostics disk that followed that particular card, or if you got the manual. Anyways, most games use the standard 4-color med-res mode so it's not too critical if your card doesn't support more than standard MGA/CGA.

Thanks for clearing this up! I so have to take a picture.

 

[sombunall]

Bad news

I tried to get 16 color grayscale in text mode with the STB The Chauffeur and failed! I wrote a basic program that tested fine on screen 0 on my main system but failed on the STB. Colors 0 to 8 are dim and colors 9 to 15 are bright. No different than TTL (or at least herculese).