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12676Re: The 1802 Elf and Serial EEPROMs

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  • jdrose_8_bit
    Mar 3, 2013
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      That is very good thinking.

      Have 2101 RAM chips at 00h to FFh and ROM from 100h and up. Latch.

      Toggle a small program in to the 256 byte RAM to jump to (EEP)ROM at 100h that copies the Spaceship code back to RAM starting at 00h. Then RUN RAM again from 00h.

      You could have many numerous 256 byte programs stored in a single 8K EEPROM.

      Genius. I am learning alot about hardware from this groupsite. Thank you.

      --- In cosmacelf@yahoogroups.com, William Donnelly <william@...> wrote:
      >
      > I would use one of the newer, larger ROMs available and only use
      > the first 256 bytes. You can tie all of the other address lines to "ground".
      > There are some electronic issues involved in that sometimes, like
      > needing to use a resistor in-line. Electronics is one of my non-strong
      > points.
      >
      > EEPROM's are nice because they can be re-programmed. Some of them
      > can be programmed in place, and don't need an external "programmer".
      > If you don't know a lot, then the easiest way might be the best.
      >
      > The way the current Spaceship program is written, it probably does need
      > RAM to operate. I haven't looked at it in awhile. But you can change the
      > memory address to be a higher block of memory, and have RAM in the
      > bottom and ROM in the higher part with the image. Or, if you want the
      > whole thing in ROM, you could make an "autoloader" pretty easy that
      > loads the first 256 bytes of RAM from a ROM using the 1802's program
      > loader functionality. That wouldn't be too hard.
      >
      > I need to get my act together and make my "punched card / paper tape"
      > and/or "sense card / paper tape" readers so that loading programs for
      > the 1802 is fairly quick and easy in a simple retro-ish style.
      >
      > -- Bill
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      > On 3/3/2013 9:45 AM, jdrose_8_bit wrote:
      > >
      > > Hello,
      > >
      > > I am gathering the parts to build a PE type 1802 Elf for testing the
      > > 1861 replacement circuit. Instead of manually toggling the Spaceship
      > > code and bitmap into the Elf I would like to burn it into a 256 x 8
      > > bit ROM of some sort.
      > >
      > > I cannot find any current parallel 256 byte EEPROMs but I have found
      > > some serial EEPROMs like the Microchip 24LC02B-E/P. I think I
      > > understand how they work. Plus they are very cheap and small.
      > >
      > > Would it be difficult or possible to use one of these 256 byte 8 pin
      > > DIP serial EEPROMs as a ROM for an Elf computer? Or perhaps recommend
      > > a 256 byte parallel EEPROM (current or obsolete)?
      > >
      > > Sorry for the simpleton questions. I am basically new to the hardware
      > > side of computers.
      > >
      > >
      >
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