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64k SRAM S100 Card

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  • Kyle Owen
    So I ve been working on designing my own 64k SRAM card for my N* Horizon. I don t ever expect to need more than 64k of RAM (hah!), so I m not implementing any
    Message 1 of 2 , Oct 15, 2012
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      So I've been working on designing my own 64k SRAM card for my N* Horizon. I don't ever expect to need more than 64k of RAM (hah!), so I'm not implementing any banking features on this. I am allowing the top 8k to be deselectable in 2k blocks, as I don't want to mask over my floppy controller at $E800.

      Anyways, I would certainly appreciate someone else looking over my schematic before I start on my layout. If you see any way I can save on ICs, or have a better easy-to-find alternative to my L2 cache chip, please let me know. I'm all about this board being user-friendly and very buildable for others needing a very cheap, possibly easy-to-prototype board, much like Michael Holley's 32k RAM card for the SWTPC: http://www.swtpc.com/mholley/QRC_Proto/32kMemoryIndex.htm


      Thanks!

      Kyle
    • Systems Glitch
      I don t have time to properly go over it before work, but I d recommend using two 62256 32K x 8 SRAMs. They re readily available (if you don t have any let me
      Message 2 of 2 , Oct 16, 2012
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        I don't have time to properly go over it before work, but I'd recommend using two 62256 32K x 8 SRAMs. They're readily available (if you don't have any let me know...I bought several hundred for a good price years ago, and I'll never, ever use them all) and if you do it right you can swap an SRAM for a 27256 EPROM or one of its EEPROM equivalents.

        You should also provide an inhibit line for your "board enable" decoder (the 74LS30). Drive it by ORing together /PHANTOM and a signal from a mask-off decoder. I'd use a 74LS682 comparator, which has a "greater than" output -- that allows you to set the high byte of your address that you want memory to be blank above.

        Thanks,
        Jonathan

        On Mon, 15 Oct 2012 23:26:04 -0500
        Kyle Owen <kylevowen@...> wrote:

        > So I've been working on designing my own 64k SRAM card for my N* Horizon. I
        > don't ever expect to need more than 64k of RAM (hah!), so I'm not
        > implementing any banking features on this. I am allowing the top 8k to be
        > deselectable in 2k blocks, as I don't want to mask over my floppy
        > controller at $E800.
        >
        > Anyways, I would certainly appreciate someone else looking over my
        > schematic before I start on my layout. If you see any way I can save on
        > ICs, or have a better easy-to-find alternative to my L2 cache chip, please
        > let me know. I'm all about this board being user-friendly and very
        > buildable for others needing a very cheap, possibly easy-to-prototype
        > board, much like Michael Holley's 32k RAM card for the SWTPC:
        > http://www.swtpc.com/mholley/QRC_Proto/32kMemoryIndex.htm
        >
        > Here's the link:
        > https://www.dropbox.com/s/rkf74guymfstu7z/64kB_RAM_board_S100.pdf
        >
        > Thanks!
        >
        > Kyle
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