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Re: [midatlanticretro] 64k SRAM S100 Card

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  • 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 1 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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