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Thread: Forcing MDA/HGC/CGA on a VGA card?

  1. #1
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    Default Forcing MDA/HGC/CGA on a VGA card?

    Folks,

    Is there a way to force a VGA card to work like (look like to software) an MDA/HGC or CGA card?

    I picked up an NIB 1987 vintage logic analyzer adapter for a PC that was intended to be used with an MDA or HGC video adapter. I have it working in a dos 6.22 P5200 with a diamond stealth 3D 2000. However, only the text based operations work with the software it came with. When I try to use the mode where it can display timing diagrams (which needs graphics support) I get an error that it can't find the graphics adapter.

    Any thoughts are appreciated.

    Lou

  2. #2
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    Default Diamond

    That's a PCI bus card, isn't it ?
    Sounds like the software you're trying to run is DOS-based.
    Just out of curiosity, are you trying to run it in a DOS-box( running the DOS app in Windows ) in a fairly recent pc( well, anything with a PCI bus) ?
    patscc

  3. #3
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    Default

    Yeah, the video card is PCI. The computer has PCI and ISA slots. It supports plug and play ISA, so I had to use the plug and play configuration utility to set the I/O port addresses for the (non PNP) 8 bit ISA logic analyzer adapter.

    I'm running real MS dos 6.22. No windows is involved here. Yes, the software (circa 1987) is dos based. It all runs fine (I've got the logic analyzer connected to a test circuit to stimulate the inputs) except the portion of the software that graphically displays the captured data. Fortunately, the captured data can be displayed in tabular form if we can't get the graphics dependant portion going.

    Lou

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    Default Cga

    Try typing mode co40 or mode co80 at the dos prompt before you load the app, see if that makes a difference. What you really is a utility that tells the graphics adapter to start up as cga. I have some for ATI cards, but none for Diamond. Anyone out there have one ?
    patscc

  5. #5

    Default

    Hi!

    I seem to recall being able to do exactly what you describe. It has to do with VESA modes or something like that. Maybe you can set your MB BIOS to expect a MDA/Herc and that might get it to work. There may be a DOS utility which can force the VGA to appear like a MDA/Herc on a VGA monitor. It will probably involve double scanning of some sort to get the monitor syncs to line up.

    Probably you are going to get your best results by just using an XT clone though. Fortunately they are pretty inexpensive if you stick with the no-name stuff. Shipping a monochrome monitor does not sound appealing though.

    Best of luck! Thanks and have a nice day!

    Andrew Lynch

  6. #6
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    Default

    Try running the attached program at the DOS prompt. It puts the VGA into double-scan mode and sets CGA mode 2.

    Since I don't know what test your program uses to determine display type, it may not fool the program. If not, let me know and I'll keep cogitating on it.
    Attached Files Attached Files

  7. #7
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    Default

    Guys,

    I tried MODE CO40, and the screen went into 40 column mode, but the software still gave the same error. MODE CO80 put it back in 80 col mode and yields the same error. I also tried setting the bios to mono, then CGA, and got the same results.

    I'm eager to try the setcga. It might be what the doctor ordered!

    Lou

  8. #8

    Default

    The problem is, I don't think any modern VGA card will emulate the Hercules at a hardware level. And you need hardware-level emulation, because there was never any BIOS support for the Herc's 720x348 graphics mode. Your program may, for example, be checking for a vertical sync pulse on bit 7 of port 03BAh, which is only present on a real or emulated Herc.

    The Paradise EGA chipset could emulate a real Herc, and I think the early Paradise VGA chipsets could as well; you'd use a DOS-based utility to set the emulation.

  9. #9
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    Yes, but many VGA cards can emulate CGA and MDA (but not MGA).

  10. #10

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    The impression I got from the original post was that the software only supported Hercules graphics.

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