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The first series of MDA adaptors for the IBM PC had the ability to show colours according to the attribute byte, much like the CGA does in text mode, but I don't remember any PC application that supported colour display on MDA.

Tommy found a modern (2018) demo by TubeTimeUS showing off with MDA colour output.

The question is not about accidentally, but explicit support. I would imagine that an application doing so would need to offer configuration settings for this usage, as there was no way to detect if the MDA is for one connected to a colour screen and equally important capable to do so, as later versions dropped that feature.

Beside setup, disabling blink mode to support background intensity instead might be another criteria to look for.

Background:

A recent question about graphic base addresses made me look into IBM's Technical Reference for the PC and remember that the original MDA had the ability to output colour. This is nicely visible on its schematics:

Page 7 of the MDA Schematics on page D-20 of the August 1981 Technical Reference, showing he forwarding of the attribute byte for fore/background as colours to the display connector

(Page 7 of the MDA Schematics on page D-20 of the August 1981 Technical Reference)

It's also in part documented in chapter 2 by using the letters R/G/B to mark the bits for fore and background, but does not elaborate any further:

Description of the attribute byte on p.2-40 of the August 1981 Technical Reference (Description of the attribute byte on p.2-40 of the August 1981 Technical Reference)

Encoding is the same as for CGA in text mode, and connecting an MDA to a CGA screen will produce colours as fine.

In the 1983 edition those connections are gone, while the description stays the same:

Page 7 of the MDA Schematics on page D-42 of the April 1983 showing no connection for the colour signals

(Page 7 of the MDA Schematics on page D-42 of the April 1983)

All chips are still there, so it might be possible to reenable this.

Raffzahn
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  • Were there any readily available, reasonably priced, color monitors that would work with the 720x350 text mode? (And there were no graphics modes in a real MDA, just in Hercules, so text is all that's possible.) – manassehkatz-Moving 2 Codidact Feb 07 '24 at 15:05
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    It doesn't provide an answer to the question, but noting that https://www.youtube.com/watch?v=-TiHFWH4NWk purports to be the output of a short colour MDA demo (i.e. not an application), in case there's any dispute. – Tommy Feb 07 '24 at 15:14
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    @manassehkatz-Moving2Codidact Sure. Text is what MDA is about. And coloured is a nice add on. Just think how much Norton Commander or other text UI gained from using colour. Also, reasonable priced is relative. The very reason why many Apple II users only had green screens, despite it supporting colour. – Raffzahn Feb 07 '24 at 15:15
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    @Tommy Nice find. I will add that if I may. – Raffzahn Feb 07 '24 at 15:17
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    @manassehkatz-Moving2Codidact The CRTC could be reprogrammed for other formats, and there are remains of supporting more than one format in the design (software selectable pixel clock and horizontal resolution, but only one clock available), and jumper JP1 to invert VSYNC polarity, control underline feature, and select another font from the chargen ROM. Incidentally, same chargen ROM was used in CGA. Colour text out from early MDA has been demonstrated in a Youtube video. – Justme Feb 07 '24 at 15:20
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    @Justme That's of course always possible - much like the CGA's famous 160x100 mode. MDA might do essentially the same as 160x175. But as mentioned, using graphic symbols with colour support goes already a long way. – Raffzahn Feb 07 '24 at 15:27
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    @Raffzahn No, the CGA 160x100 "mode" is identical to 80x25 text mode with scan lines per character set to 2. What I mean by reprogramming is to change the horizontal total pixels (characters) per line to adjust HSYNC rate and vertical total lines per frame to adjust VSYNC rate. For example you can reprogram an EGA card to output timings suitable to MDA monitor. – Justme Feb 07 '24 at 15:45
  • "All chips are still there, so it might be possible to reenable this". There's a post on vcfed.org showing an MDA with the connections reinstated using patch wires: https://forum.vcfed.org/index.php?threads/a-strange-hidden-feature-of-the-ibm-mda-card.62616/post-757059 – john_e Feb 08 '24 at 12:26
  • @john_e Lovely. Thanks for searching. – Raffzahn Feb 08 '24 at 15:34

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