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Thread: Best way to get UMBs on a 286 board with no chipset support

  1. #1

    Default Best way to get UMBs on a 286 board with no chipset support

    Recently purchased a VLSI 286 board using the VL82CPCAT-QC chipset (VL82C102-QC memory controller.)

    This chipset offers no shadow RAM, EMS, or (disabling) memory relocation options. All onboard RAM beyond 640kB is "hard wired" to XMS.

    I'd like to make some UMBs for drivers, as well as potentially get a EMS card for the cross section of software that uses it.

    So far the options I've determined for getting some usable UMBs are:
    1) umbherc.sys - I was planning on installing a TD3088A Hercules clone anyway (in addition to VGA) for the use of a TTL mono CRT as a secondary display. Don't plan on using any graphical or Hercules specific features, so the VRAM on the herc card would be mostly unused without the driver. Downsides to this approach are people have had trouble getting the driver to work, and being limited to 8-bit memory access for my drivers in UMB.

    2) get a lo-tech 1MB RAM card and enable whatever ranges I can that don't contain option-ROMs or necessary video RAM - This would certainly provide 2-3 more pages of UMBs than the hercules option, but the 8-bit access penalty would still apply.

    3) purchase one of the various 16bit EMS cards - this would provide EMS as well as some extra XMS. Are any of these cards capable of providing UMBs? Obviously they would provide an EMS page frame in the UMA, but I wonder if any of them can be configured to also map some of their memory as UMBs for drivers etc. Memory access would be 16-bit, and only penalty relative to the onboard RAM would be an additional wait state probably.

    What do you guys think is the best way to handle this?

  2. #2

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    Have you looked at or tried USE!UMBS.SYS? If not, it's certainly worth a look.
    PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

  3. #3

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    Quote Originally Posted by Stone View Post
    Have you looked at or tried USE!UMBS.SYS? If not, it's certainly worth a look.
    USE!UMBS.SYS requires the presence of physical RAM in the UMA does it not? This chipset (I have the datasheet) specifically says it does not map any physical RAM in the UMA.

    I don't actually have the board in hand so I can't run TEST!UMB to verify, but I'm not holding out much hope.

  4. #4

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    Quote Originally Posted by maxtherabbit View Post
    USE!UMBS.SYS requires the presence of physical RAM in the UMA does it not?
    Not necessarily -- there are other possibilities it can provide. Look into it.
    PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

  5. #5

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    Quote Originally Posted by Stone View Post
    Not necessarily -- there are other possibilities it can provide. Look into it.
    I just read all of its documentation - it does in fact require the presence of physical RAM in the UMA. It doesn't have to be on the motherboard (you can repurpose video RAM from MDA/herc/CGA/EGA/VGA adapters) but that would be essentially doing the same thing for me as umbherc.sys, unless I was willing to sacrifice VGA graphics modes, which I am not.

    I am somewhat unclear on the B800-BBFF range. My understanding was that it was traditionally not safe to use this range if you have a VGA adapter because it uses at least part of it for textmodes (in lieu of B000-B7FF.)

  6. #6

    Default

    Quote Originally Posted by maxtherabbit View Post
    ... but the 8-bit access penalty would still apply.
    This penalty isn't that bad. Only DOS resides here so only when DOS needs to be accessed, the system becomes a bit slower. You, as an user executing some commands like DIR etc., won't notice at all IMHO.

    3) purchase one of the various 16bit EMS cards - this would provide EMS as well as some extra XMS. Are any of these cards capable of providing UMBs?
    I have had an EMS card where the page and its size could be set by hardware. That page can be used as UMB. But IIRC the maximum size of the page was 16 KB, just good enough for a mouse driver or so.

    Some ideas that you can use maybe:
    - I built my own 128 KB UMB board using a 128 KB SRAM. Can be quite simple. If interested, I'll look it up for the schematics. OK, just 8-bits because that was the most simple way.
    - There is this memory expansion card for the IBM-PC that enables the memory to be expanded from 256 KB up to 640 KB. With dip switches it can be told that the memory should start at 0D0000h. But before this memory can be used, it has to be written and read once with the parity checker off. I created my own version of USE!UMBS.SYS where this is done. OK, again only 8-bits but....
    - Really just an idea: find a 128 KB 16-bits expansion card meant for the original IBM 512 KB AT boards and hack it so the memory appears at 0D000h. But again: set the parity first.

    Last remark: check whether your AT uses the 0E000h area or not.

    Have fun!
    With kind regards / met vriendelijke groet, Ruud Baltissen

    www.baltissen.org

  7. #7

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    If the 8-bit RAM accesses are no big deal, it sounds like the cheapest and easiest options would be to use the memory on the Hercules (carving out 4k each at B000 and B800 for textmodes) and/or just buy a PCB for the lo-tech 1MB RAM card and build it.


    Are there no EMS boards that provide an option to create usable UMBs *in addition to* the page frame? That would be the cleanest option if it exists

  8. #8

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    Quote Originally Posted by Ruud View Post
    Last remark: check whether your AT uses the 0E000h area or not.
    it does

    checkit finds system ROM from E000-FFFF

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