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Thread: Use of ems on a 8088 xt

  1. #61

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    Quote Originally Posted by ropersonline View Post
    Waaaait a minute... How quickly could that thing switch fonts? Could the switch have occurred between two scanlines?
    IIRC there was nothing to suggest that it can do any switching at all under software control - only manually. But then, that thing came in a used 5155 with no documentation whatsoever. The actual fonts in there are all different encodings for ASCII containing the Greek alphabet... perhaps because DOS code pages weren't yet standardized yet at that point in time. The thing is also hooked up to the LPT port in some way, so who knows what the point was. Could've been for a very specialized usage.

    Applause for the effortpost, but I have to say that in my experience (and I have some ), the most glaring problem when "faking" APA using text mode is the attribute clash - meaning it's a bigger artistic limitation than the lack of every conceivable pixel pattern. More of those would help, but in a "diminishing returns" sort of way, as long as you're limited to two colors per group of eight pixels.
    The already-mentioned CGAArt reads the the font bitmaps from an image of the CGA character ROM, so you can actually test that theory by modifying that image with the 256 different 8-bit patterns and seeing what happens even with one scanline per row.

    If you're already spitballing ideas that require hardware modificiations, IMO, you might as well do a redesign with more RAM rather than ROM, and get an extra bitplane or three to decode for real 16-color APA modes!
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  2. #62
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    Quote Originally Posted by VileR View Post
    If you're already spitballing ideas that require hardware modificiations, IMO, you might as well do a redesign with more RAM rather than ROM, and get an extra bitplane or three to decode for real 16-color APA modes!
    Heh. I was thinking of suggesting the same thing. Lots of contemporary computers implemented color graphics as bitplanes back then. (For the decent reason that it significantly reduces the speed at which you need to clock the memory compared to "chunky" pixels if each plane is in its own memory bank.) It'd be a pretty ugly mod but in theory if you just piggybacked three additional sets of 16k RAMs onto the existing one in the card, added an output latch and shift register for each plane, an input multiplexer to select which one the CPU is reading and writing to, and directly shunt the output of each shift register straight to the RGBI connector (each plane would control the corresponding pin) then, bang, you basically have the 640x200 EGA mode. (With the one complication that it's still 2:1 interlaced like CGA... and no palette register unless you add one.)
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