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Re: [cosmacelf] Bootstrapping with a friend

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  • Lee Hart
    ... Hot swap is harder, because you have to worry about making the power and ground connections first, and then holding the logic levels to a safe level until
    Message 1 of 5 , Mar 19, 2013
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      On 3/18/2013 12:38 PM, William Donnelly wrote:
      >
      >
      > How hard would it be to make "hot-swap" 'cartridges' like old-style
      > (new-style?)
      > video games, so you can just plug in a "ROM" program. Or even ROM/RAM,
      > whatever.
      > Or cold swap. Whichever is easiest / cheapest and doable.

      Hot swap is harder, because you have to worry about making the power and
      ground connections first, and then holding the logic levels to a safe
      level until they are all properly connected.

      The classic video game cartridges used connectors with the power and
      ground pins longer than the others, so they connected first. They
      contained read-only memory, so there was no danger of accidentally
      changing the data.

      If the cartridge has RAM in it, then it has to include a way to write
      protect the RAM when it is removed and while plugging it in or out.

      The device the cartridge is being plugged into also needs to make some
      allowances. Plugging it in can't glitch the power supply. For example,
      the cartridge can't have a big filter capacitor that momentarily shorts
      the power supply before it charges. It needs some series impedance to
      limit the peak current.

      Similarly, the data lines need buffers so the cartridge can't "glitch"
      them high or low during plugging or unplugging and so crash the computer.
      --
      Ring the bells that still can ring
      Forget your perfect offering
      There is a crack in everything
      That's how the light gets in.
      -- Leonard Cohen, from "Anthem"
      --
      Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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