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6669Re: [cosmacelf] Free Running .pdf

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  • Lee Hart
    Apr 5, 2010
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      Rick Cortese wrote:
      > It's a cute design, got me thinking.
      > I think I would like a minimal system.

      Are you looking at the "1802 free running" file? It is just using the
      1802 as an 8-bit counter. While it is certainly minimal, it also doesn't
      do much.

      You may want to look at some of my Membership card designs. These are
      intended as minimal Elf-type computers that really do run as computers.

      > I Still have some other obsolete parts like a 6810.

      That's a 128 byte RAM. It would work fine with an 1802 if 128 bytes is
      enough. Most Elf computers had at least 256 bytes.

      > I'm thinking it would be cute to do something like use the standard
      > upper 8 bits address latch but have its outputs tied in a resistor
      > ladder DAC. To output $FF to the latch you would just load a register
      > with anything in the $FFXX range and discard it.

      This would work, but not very well. The high address latch will get set
      on every single bus cycle. Some of these latch a real address, from the
      upper half of a register. But many of them will latch "nonsense" -- it's
      predictable, but not easy to account for in your software. If you are
      trying to make decent audio, it would likely punch it full of noise
      without extremely careful programming.

      It would be so much easier to use Q as your serial output to produce
      audio. You can set it high/low any time you like, with no side effects.

      Lee A. Hart | Ring the bells that still can ring
      814 8th Ave N | Forget the perfect offering
      Sartell MN 56377 | There is a crack in everything
      leeahart earthlink.net | That's how the light gets in -- Leonard Cohen
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