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Re: [cosmacelf] membership card + elf2k ROM ?

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  • Lee Hart
    ... There are several ways you can do this. 1. You can load a program into RAM, and maintain power to keep it there. 2. Same thing, but use a nonvolatile RAM,
    Message 1 of 2 , Aug 31, 2013
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      Mark G Thomas wrote:
      > So, I'm putting together a membership card in a slightly larger case than
      > an altoids tin, and I got to thinking it sure would be nice if it had a
      > ROM monitor, and I could put a serial port on my enclosure.

      There are several ways you can do this.

      1. You can load a program into RAM, and maintain power to keep it there.
      2. Same thing, but use a nonvolatile RAM, like one with the piggyback
      lithium cell, or a ferroelectric RAM. This way you don't need to
      maintain power.
      3. You can build a ROM board, as designed by Richard or Herb Johnson.
      These are basically a binary counter to provide sequential addresses
      to a PROM or EPROM. Plug it in to the 25-pin front socket, and its
      contents is automatically loaded into RAM.
      4. Get a 2nd Membership Card (rev.D or later). There are provisions to
      stack the two, with a ROM on one board and a RAM on the other board.
      Now you have both ROM and RAM, as well as a second I/O port.
      5. I'm sure there are other ways as well. I can imagine piggy-backing
      two memory chips (one EPROM, one RAM), with one of the address lines
      used to chip-select between the two.

      --
      The most dangerous enemy of a better solution is an existing one that
      is just good enough. -- Eric S. Raymond
      --
      Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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