Recent content by reenigne

It's number 3 - All the 6x opcodes are aliases of the corresponding 7x (conditional jump) opcodes on 8086 and 8088.

That's exactly the bug. Yes, I noticed a few monitors/TVs get confused by the lack of a color burst. Not disabling colour (and getting random animated rainbows as a result) is one of them. Another is the gain being set to normalise the burst amplitude, which (with no burst to amplify) results in...

No, it's really a bug because it also slightly truncates the horizontal sync pulse, taking it further from NTSC specifications (though the shortened pulse still works fine with CRT monitors). There's also no need for it, since there is a separate +BW bit to eliminate the color burst to make 80...

Yes, it's expected to not get colour by default in 80-column text mode - there's a design flaw with the CGA card that suppresses the color burst in this mode (and IBM didn't bother to fix it since colour text is not very legible in 80-column mode).

The C1 position is fine in c1.JPG. If the image isn't stable with the capacitor in that position there's another problem. It could be an issue with the sync circuitry on your card, but more likely is that the TV you're using is being overly picky about the signal - even when it's working...

At least for Turbo C (not sure if it's the same for Watcom) the huge memory model also relaxes the 64kB limit on static data, which might be the critical assumption here. Depending on what the generated code is actually doing, the large or even compact model might be sufficient.

I can't tell for sure without looking at the generated assembly, but my guess is that it's assuming that DS (and possibly also SS) points to the segment containing _vchar, _vcol and _voffset. This is true if the function is called from other C code but the interrupt could be interrupting some...

There are a few reasons why we picked 640kB as our specification rather than some smaller amount of RAM. Most 5150/5160 machines in the wild have 640kB as it was a common upgrade to extend their useful lifespan, and ISA RAM boards are not rare. Although it was not a stock IBM configuration (and...

I hadn't come across Mindset before but a quick Google search says that it can do 16 colours from a palette of 512. Whereas the 15 colours in the mode that most CGA composite games (including Commander Keen) use are fixed. This probably accounts for most of the difference - I expect that if the...

Some of the effects could be done that way, but a lot of them rely on the fact that the CGA uses the same crystal for a timebase as the CPU and/or the PIT. VGA uses a totally different crystal so the demo would have to spend a lot more time figuring out where the raster beam is.

CGA doesn't allow for redefining the character set - it's in ROM. But you can change the height of the characters. Much of the demo is done in text mode with the number of scanlines per row of text reduced from 8 to 2 or in some cases 1. Some of the effects are more sensitive to the details of...

Yes, even the end credits sound is PC speaker (using PWM with the timer in mode 0). Yes, the video output is 4-bit TTL RGBI - there are only 16 colours in the whole demo. Any impression of more colours is done by dithering. The party capture at the beginning of the thread looks like it has other...

Thanks! No, no Sound Blaster is needed or used - all the sound is done through the 1-bit PC speaker.

I think Area 5150 will partially run with 512kB but (from memory) it'll stop rather than skip parts when it runs out. I'm not sure how much of the demo you'll be able to see - it may depend on how much memory the version of DOS you use takes up.

Here's a better capture: I'm one of the authors of this demo, if anyone wants to ask questions about it.