I'm fairly new to these forums so I thought I better ask what the correct etiquette is. I'm writing up a post on some of the secrets of the IBM MDA. It's not mega long but it is reasonably involved. Should I post a link to a blog post, or is it ok to have forum posts with lengthy discussion about …

Sorry ignore that, I see you answered already further up..

Yes, EGA is a bit of a weird standard. The 200-line modes are deliberately designed to be backward-compatible with CGA monitors. Which ironically means that you're stuck with the 16 fixed RGBI colours in 320x200 and 640x200, even on an actual EGA monitor which has 64 RGBrgb colours. There's a dip- …

I notice it's the classic Chips & Technology chipset. C&T were one of the first companies to clone the EGA. Top Left: 82C431 Graphics Controller Top Middle: 82C433 Attribute Controller Top Right: 82C432 Sequencer Middle: 82C434 CRTC And an EPROM on the bottom obviously Any idea what the other gate …

CGA cards, by contrast, always* use 200 lines. That's all they can do. Otherwise, they'd be Hercules compatibles. ;) - Because, both use the same text character generator chip. This is what fascinates me about the CGA on the IBM PC. The CGA and the MDA arrived at more or less the same time, but …

The VGA only has a 25Mhz and a 28Mhz physical clock chips on board, so this tends to dictate a lot of the decisions they made regarding keeping backward compatible low-res modes on newer higher frequency displays. With the CGA all the timing is coming straight from the system board. I didn't know …

You might want a better EGA reference, but yes this seems correct. Programmer has enabled all four maps in the map mask register of the Sequencer Then set data rotate as zero in the GC. Then set write mode 2 in the GC Then has selected the bit mask register in the GC

The CGA does not 'pixel double' anything. It sends pixels to the display at a rate typically called the 'dot clock' - in the high res 640x200 mode it is sending pixels at twice the rate, so twice as many appear on a scanline. In the low res mode it is sending pixels at half the high res rate. No ' …

If anyone is interested I created an Issue on 86Box github about the broken EGA behaviour on split screen handling... https://github.com/86Box/86Box/issues/3386 I patched my own build and it seems to work but I don't really know much about pull requests and all that malarkey i'm a bit of a github …

From what I recall the ET4000 was considered one of the best chips for DOS performance. So I would be surprised if the S3 topped it. But that is my hazy memory from about 30 years ago.

First things first, selecting colours with the map mask register is not ideal. If you set all the pixels in a byte white (map mask = 0Fh) then when you subsequently try and set a pixel some other colour like blue, you are not making the data in the other planes go away by masking it - all a masked …

Panning works the same way in EGA and VGA, modulo some quirks such as how split-screen operation is affected. Panning in split-screen is operating in a way on EGA that was considered quirky in practice, I'm new here, so hi folks!!! :-) I'm writing a game for the EGA and split screen is as far as I …