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Thread: A "new" XT clone - ATX board

  1. #11
    Join Date
    May 2016
    Location
    Fairfield, Ohio
    Posts
    486

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    I hope it's cheaper than the NUxt, because $340 is far outside my price zone.

  2. #12

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    Visit https://jlcpcb.com/ and find out what they charge for five boards of 9.5" * 9.5". About $25, I think. What the parts will cost, I don't know. You have to creative here: I am going to use IS-slot connectors from boards that could not be repaired. These boards also donated a lot of the needed ICs.

    To give you another example: I have built a XI-8088, with two exceptions, from scrapped parts only. The exceptions are the board itself and the VT82C42 keyboard controller. Then you should be able to figure out how much the nice system costed me.
    With kind regards / met vriendelijke groet, Ruud Baltissen

    www.baltissen.org

  3. #13

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    Hi Ruud, I really liked your design. The schematic is a bit difficult to follow because its too big to fit a screen. You reminded me of a similar project I tried to do a couple of years ago. Unfortunatly for me I never built my board. I'll attach my schematic and PCB yours looks way better than mine. If anyone is interested let me know and I'll try to find the eagle files I think I have them somewhere. My idea was to build a simple XT motherboard that would boot DOS for educational purposes. I've also been trying to simulate in Proteus a minimalistic system that would boot DOS but so far I haven't been able to boot it. Also if anyone would like to comment on my design I'll appreciate it. Thanks!
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  4. #14

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    Thank you!

    I found some nice things in your design: the way you created the IOxx and MEMx signals and the way you are able to use a PS/2 keyboard. And don't worry about booting DOS, Michał Pleban managed to boot MS-DOS 3.30 on a Commodore 720 equipped with my 8088 card and that went fine. And without using DMA. The DOS was loaded from a SD card that was bitbanged with a 8255. But the DOS ran! The only thing you really need is a good BIOS. If you have a BIOS that cannot serve DOS like it wants and things won't work.

    Regarding my big schematic, I never liked the feature of dividing it in several pages. But starting last weekend I changed one thing: so far I drew all buses all over the sheet and I stopped doing that. I will keep drawing all single lines but will only draw a piece of the bus.

    PM me and you can get my Eagle files.
    Last edited by Ruud; September 22nd, 2020 at 11:11 PM.
    With kind regards / met vriendelijke groet, Ruud Baltissen

    www.baltissen.org

  5. #15

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    I also did the bitbanging with the 8255 to load DOS into memory. I guess I'm doing something wrong in my BIOS that prevents DOS from booting. I'm going to post a new thread about that and I'll post the code. I think its very usefull to have a working simulation of a system that boots DOS. I havent seen anyother project like this online. Do you know what DOS need to boot from the BIOS?

  6. #16

    Default Booting DOS from an 8086 simulation with Proteus


  7. #17

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    Quote Originally Posted by NicolasF View Post
    Do you know what DOS need to boot from the BIOS?
    The only lame answer that I can give is the one I gave in a previous message: a good BIOS. Michał used a logic analyzer to find out where things went wrong. IMHO Proteus must have an equal tool.

    But as said: the CBM doesn't have DMA. So what about loading DOS without using DMA? In that way you can keep track what your computer is loading and where it is saving the data.
    With kind regards / met vriendelijke groet, Ruud Baltissen

    www.baltissen.org

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