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Thread: EGA and 64 colors mode

  1. #1

    Default EGA and 64 colors mode

    My colleague from ours Old Computer forum discovered, that game Ironman Offroad support unusual game mode. There are not many games with this graphics mode.
    64 colors on EGA, resolution is 320x200 of course. All you need is multisynch EGA monitor with support of 64 colors.
    Common EGA monitors works only on 16 colors mode.
    Difference is noticeable

    IMG_7226.jpg 16 colors
    IMG_7227.jpg 64 colors
    IBM PC 5150(A): IBM PC 5150(B): IBM PC 5160 (64-256k): IBM PC 5160 (256-640k): IBM PC 5170 (099): IBM PC 5170 (319/339): IBM PC 5140: IBM PC 5162: IBM PC 5155:
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  2. #2

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    Rambo III also supported this, plus a few others. AFAIK it's still a maximum of 16 colors at a time, although the possible range is 64 (6-bit 'RGBrgb' like in hi-res EGA).

    Doesn't this mode require specific EGA *chipsets*, as well as a multisync monitor? I seem to remember that at least one of those games only offered it for Boca and Paradise cards, with a very prominent "CAUTION!" text too. I don't think a standard IBM EGA will do this, since its 200-line modes are limited to a CGA-like IRGB signal.
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  3. #3

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    Confirmed, works also with IBM EGA (256k)
    IBM PC 5150(A): IBM PC 5150(B): IBM PC 5160 (64-256k): IBM PC 5160 (256-640k): IBM PC 5170 (099): IBM PC 5170 (319/339): IBM PC 5140: IBM PC 5162: IBM PC 5155:
    WANTED! : IBM 5161 Expansion unit, IBM 5175 monitor, IBM 5145 monitor, IBM EGA Graphics Memory Expansion Card, IBM PC screws,
    My IBM PC hardware collection

  4. #4

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    The trick here is to change the vertical sync polarity in 15.75khz mode. Switching it to negative polarity should allow for RrGgBr 6-bit color palettes and it might even work with IBM's EGA monitors. Many of the early multiscan monitors like that Princeton and the NEC Multisyncs had a switch to force 64 color mode. The limitation of RGBI in 15.75khz is entirely artificial to maintain backwards compatibility with CGA monitors, but that never stopped anyone.....

  5. #5

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    Yes, but is it possible to force *any* standard EGA card to output a negative vsync in 15.75KHz modes?

    If it is, why does this game require Boca/Paradise chipsets for the 6-bit palette, and support only RGBI for the 'standard IBM type'?
    If it isn't, how does Super Off Road pull it off on an IBM EGA (according to romanon)?

    Something doesn't add up. It's possible that Rambo III is doing something completely different, like using those chipset extensions to generate 400 lines at 22kHz as a double-scanned version of the 200 line modes, but I doubt it.
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  6. #6
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    Very interesting this game support the 64 color mode.
    I use a ibm cga monitor connected to a ega card (this was the most common configuration) when you use this combo theres only 1 intensity pin so 16 colors.
    When you have a true EGA monitor they are 2 intensity pins present for the digital color signal that's what give you the extra 64 colors.
    And it's enable only when you select the high resolution modes like 640x350 24hz mode.

  7. #7

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    According to Rambo III. This game never promise to display 64 colors, all modes to select are in 16 color range.
    541305-rambo-iii-dos-screenshot-setup-menu-for-run-on-ega-enhanced.jpg

    This is image of RIII screen in normal EGA mode
    IMG_7239.jpg
    and in enhanced EGA mode with ??? colors
    IMG_7238.jpg
    Its different, but i can't count how much colors there are

    About IBM EGA and 64 color mode, i am little bit confused right now.
    This is picture of nonIBM EGA in 64 color mode
    IMG_7227.jpg
    but IBM EGA shows that screen slightly different
    IMG_7241.jpg
    Is there really 64 color palette? I don't know, i cant count them
    This is standard EGA 16 color mode on IBM EGA
    IMG_7242.jpg

    Its hard to judge this results only by eyes review. We need some utility or simple Basic program to check real 64 colors palette. So anyone?
    IBM PC 5150(A): IBM PC 5150(B): IBM PC 5160 (64-256k): IBM PC 5160 (256-640k): IBM PC 5170 (099): IBM PC 5170 (319/339): IBM PC 5140: IBM PC 5162: IBM PC 5155:
    WANTED! : IBM 5161 Expansion unit, IBM 5175 monitor, IBM 5145 monitor, IBM EGA Graphics Memory Expansion Card, IBM PC screws,
    My IBM PC hardware collection

  8. #8

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    Quote Originally Posted by romanon View Post
    According to Rambo III. This game never promise to display 64 colors, all modes to select are in 16 color range.
    It's never 64-colors but 16 simultaneous colors out of 64 palette.

    The other modes are fixed CGA 16 color palette style including the brown "fix" over bright yellow.

    This is really interesting, so if it is possible to use this mode in any EGA card then I might take a look on the mce2vga code. Also the game needs to run on PC-XTs... But it is tricky as it would be playing with the vertical sync time instead of the polarities...

  9. #9

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    Quote Originally Posted by soviet9922 View Post
    When you have a true EGA monitor they are 2 intensity pins present for the digital color signal that's what give you the extra 64 colors.
    There is no second intensity pin, rather 6 pins used for color - 2 each for R, G, and B (so no intensity signal at all, in fact).
    R, G, and B plus two intensity pins would give you only 32 colors (2^5), which would look quite different besides.

    Quote Originally Posted by romanon View Post
    According to Rambo III. This game never promise to display 64 colors, all modes to select are in 16 color range.
    Yep, 16 simultaneous colors, but in The "enhanced" EGA modes those 16 are selected out of 64 possible colors. The VGA version also supports 16 colors (out of 2^(6*3)=256K colors).
    I don't know of any way for an EGA card do display 64 simultaneous colors in any mode (there aren't enough bitplanes).

    Quote Originally Posted by romanon View Post
    This is image of RIII screen in normal EGA mode
    IMG_7239.jpg
    and in enhanced EGA mode with ??? colors
    IMG_7238.jpg
    Its different, but i can't count how much colors there are
    The second one looks like it has less colors than the first (compare the "banding" on the arm, and on the left side of the helicopter)... also, those colors all look like they belong in the standard RGBI palette. Is that on an IBM EGA?
    If so, my semi-educated guess is that the game is trying to send 6-bit values to the palette registers, but only 4 bits are used -- that's what the IBM EGA is known to do in 200-line mode. This produces a different palette compared to the "standard" EGA shot, but colors are quantized to RGBI values so it is definitely not as intended.

    Quote Originally Posted by romanon View Post
    Its hard to judge this results only by eyes review. We need some utility or simple Basic program to check real 64 colors palette. So anyone?
    I don't have the hardware to test such code, but your photos actually increase my confidence that my conjecture is correct - both games show 16 out of 64 colors on "extended" EGA, and plain old 16 RGBI colors (just not the correct ones) on a standard IBM EGA.

    Quote Originally Posted by romanon View Post
    About IBM EGA and 64 color mode, i am little bit confused right now.
    This is picture of nonIBM EGA in 64 color mode
    IMG_7227.jpg
    but IBM EGA shows that screen slightly different
    IMG_7241.jpg
    Is there really 64 color palette? I don't know, i cant count them
    This is standard EGA 16 color mode on IBM EGA
    IMG_7242.jpg
    The first shot again does not look like it has more than 16 (simultaneous) colors. At least, it looks quite similar to this VGA screenshot, and that one is definitely 16 colors (you can verify that in software).
    About the second shot, it's hard to tell because the photo came out kind of greenish, but I'm fairly confident that the colors here are RGBI ones. Which points to the same symptom as Rambo III on the IBM card: the game reprograms the palette using 6-bit values, but only 4 are actually used.
    int10h.org :: :: :: blog

  10. #10

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    Quote Originally Posted by VileR View Post
    The second one looks like it has less colors than the first (compare the "banding" on the arm, and on the left side of the helicopter)
    The second Rambo image looks like it's truly to emulate the Commodore 64 color palette. Maybe they got lazy and just copied the artwork from the C64 version of the game?


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