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Re: CGA Composite Mode under DOSBOX?

Posted on 2012-06-02, 07:03

I have updated the PCjr portion of the images. I had matched the PCjr to DosBox, now I have matched it to the captures. Palette 0 color 2 is now more like brown (though I would disagree about it being a "reddish" brown), and 640x200 mode now looks like new CGA.

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-06-01, 17:55

In preparing an overhaul of Wikipedia's CGA article to incorporate the new findings since 2008, I have created example images showing direct and artifact colors of all the major CGA revisions. I haven't seen a capture of the PCjr in 640x200 mode, so those colors might be completely off.

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-05-13, 19:20

If you really need to use function keys at all, please at least let me set an initial hue and brightness setting in the configuration file. For most games, it becomes quickly obvious which setting is best, and I shouldn't have to adjust it with function keys every time I run the game. New CGA may be …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-05-01, 21:44

It's probably just that your TV doesn't have a proper "colour killer" circuit According to the service notes, all color processing is done by the Motorola MC44002P "Chroma 4 Multistandard Video Processor", so beware. An interesting experiment to do would be to making the entire screen a single …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-05-01, 20:37

It's 1 multiplication if performed before YIQ separation or 3 after. You'll have to do more than one multiplication for S-Video or RGB inputs anyway. Since all modern TVs, and European TVs since 1980 or so, have to be able to handle RGB signals, applying contrast to the RGB signals will be the …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-05-01, 18:56

I = average(sin(t*2*pi*3.57MHz)*C) Q = average(cos(t*2*pi*3.57MHz)*C) I don't understand that. Why average? doubling composite (the active picture part, not including the color burst). Well, there's the rub. Any automatic gain control would apply to the whole signal, not just the active picture …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-05-01, 16:31

f12 - toggles emulated monitor type (composite, rgb, auto) f11 - toggles hue/brightness/contrast/saturation/cgaversion ctrl-alt-f11/ctrl-alt-12 - adjusts what was chosen by f12 What for? These settings are set once per game, and then never again. They belong in the config file, as they don't need …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-05-01, 07:24

My TV does use the color burst amplitude as an amplitude reference, but not just for saturation purposes - it uses it to normalize the gain for the entire signal That's what I found, too. Because the Tandy outputs the same too low burst amplitude as the new CGA, the TV amplifies the signal like …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-30, 22:10

You will notice that my Sony TV doesn't show the monochrome modes as monochrome. That may either be the fault of the Sony TV, or there's some 3.58 MHz signal leakage in the Tandy's composite output, which the TV takes as a very weak color burst signal. And as you can tell, this TV has no comb filter …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-30, 19:59

Oh, we calculated the same amplitude values independently of each other. I am so proud of myself. By the way, I have a Tandy 1000 TX on which I can do some tests, if desired. Because the final output signal is a weighted sum of the chroma and +I (intensity) signals (and, for new CGA cards, the +R, …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-30, 18:52

reenigne wrote: because of the reduced chroma amplitude in the new card there's almost no relative delay between the pixel clock and the chroma signals, so the two cards do differ in hue by about 13 degrees. Why is the delay a function of the chroma amplitude?

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-28, 19:32

maybe they just never got around to writing that little refinement to the background drawing routine. That's what I suspect, too. Keep in mind that in the case of Bruce Lee, you are dealing with what was originally an Atari 8-bit game. Ports were not necessarily done with a lot of thought. For …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-27, 17:00

Here are my screenshots for Bruce Lee and Decathlon For what it's worth, attached is Decathlon with my current algorithm (and a delay of 14 MHz and 3.58 MHz of -15 degrees) and full overscan. (Edit: apparently including the overscan makes the image too large for this forum to display it inline, so …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-25, 20:15

The active (i.e. video-memory driven) Which signal now? "Active" in composite video parlance refers to the start of what would be called the overscan area. There's no equivalent in video parlance for the "display" (i.e. non-overscan, coming from video memory) area, although "title-safe" and "action …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-25, 19:15

That's not right - the width of the hsync pulse I'm talking about the CRTC's HSYNC signal, not the composite hsync pulse. So the centering calculations should be correct in theory, although I don't know how monitors and TV cards react to the unusually long non-sync period. I would suppose they just …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-25, 18:38

HCLK is a 1.79MHz signal (the CRTC clock in 80-column text mode) and LCLK is a 895KHz signal (the CRTC clock in other modes). So the sync pulse timings are all the same in two modes except... So the character clock is always constant given a particular mode register setting? I had hoped that it …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-25, 17:00

Here's what happens on the 1501486: Thanks for the explanation. A couple of questions: What exactly is a HCLK and LCLK? I'm asking because I don't quite understand how this translates to high-resolution text mode, although I have read that it makes the color burst unusable. Does that mean that the …

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