A strange hidden feature of the IBM MDA card...

[Retro Canada]

Sorry for a bit offtopic, but if CGA card contains Color/Mono switch, does it mean it contains MDA and CGA? Is it offering real MDA or is it just CGA converted into single color? MDA outputs green color?

If it's MDA, does it make contradiction to IBM 5150's motherboard switch settings? I would like to have both CGA and MDA but I like the idea that I could switch between them without need to open the case each time and set the motherboard's switches manually.

I have one of these Color/Mono switch cards and it is indeed a MDA signal 9x14 characters that it outputs. And in MDA mode it outputs some deegree of color information because I get some light cyan/purple when displaying it in color mode.
I changed its character set because it was ugly. I use the standard now. I had to generate the rom in the correct format for it. You can't get an CGA/MDA rom and put on it...

 

[ejs]

Which model NEC monitor are you using? I have a JC-1401P3A. I don't have a manual for it and don't know if it could be hooked up with a straight through DB9 cable to an MDA, CGA, or EGA display adapter, and how all of the various switches would need to be set.

I think that's the same as mine. On the back, set the switch to digital. Auto mode works ok, if you use manual then set the DIP switches for 16 colors. On the top of the monitor, make sure the text switch is off. You'll probably need to adjust the vertical hold and position.

 

[Casey]

I wonder how an old Compaq amber monitor, capable of hi-rez text or CGA graphics would react to this...

 

[ejs]

That would be interesting. I also happen to have one of those Compaq combo MDA/CGA cards. There's apparently a mode bit that you set to switch between MDA and CGA.

 

[romanon]

Interesting, some games are color, some not. Norton Commander and also Volkov Commander are still monochromatic.





In fact, in old MDA we have hires color text mode in (theoretical) 720 × 350 pixels, what is more than hires EGA. But only with 4kb of video ram.

 

[Great Hierophant]

I do not like to necropost, but here is a video I made capturing the color MDA in action: