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Re: [cosmacelf] Re: The 1802 Elf and Serial EEPROMs

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  • David W. Schultz
    ... Then perform a simple upgrade: 1) Add a CD4042 to latch 4 bits of address. 2) Replace the 22 pin sockets for the 2101 SRAMs with a pair of 24 pin sockets
    Message 1 of 20 , Mar 9, 2013
      On 03/08/2013 11:38 AM, jdrose_8_bit wrote:
      > Actually, I do not mind typing in programs. It is toggling in
      > programs that has sorta lost it's novelty. :-)
      >
      > Also, I would like to be able to save any programs that I develop for
      > the PE ELF. Some sort of ROM seems like the simplest and most cost
      > effective way to do it that the Elf can use directly.
      >

      Then perform a simple upgrade:

      1) Add a CD4042 to latch 4 bits of address.
      2) Replace the 22 pin sockets for the 2101 SRAMs with a pair of 24 pin
      sockets wired for 6116 2KX8 SRAMs.

      Now you have a lot more memory to play with but more importantly, a
      non-volatile option. If I read the 28C16 datasheet from Jameco right, it
      is a drop in replacement for the 6116 and even better requires no extra
      hardware to program. Just leave it alone for a bit after strobing the
      write enable line.

      Now you have a couple of choices:

      1) Put the 28C16 in the low socket and program it using the load mode.
      2) Put it in the high socket and program using a simple program. Perhaps
      a variation on ETOPS.

      You might want to add a write protect jumper to the socket with the EEPROM.


      --
      David W. Schultz
      http://home.earthlink.net/~david.schultz
      Returned for Regrooving
    • jdrose_8_bit
      ... That is an interesting option. A CR2032 would probably be enough for a while. I am not much of an EE but I doubt that it would take a complicated circuit
      Message 2 of 20 , Mar 21, 2013
        --- In cosmacelf@yahoogroups.com, Lee Hart <leeahart@...> wrote:
        >

        >
        > Another option is simply to battery back up your RAM, so it simply
        > retains the data as long as the batteries last. With CMOS, this can be
        > many years!
        >


        That is an interesting option. A CR2032 would probably be enough for a while. I am not much of an EE but I doubt that it would take a complicated circuit change to the PE ELF to do battery backup for the RAM.

        Relatively inexpensive way to go.
      • jdrose_8_bit
        ... I was able to find it. Thanks! http://www.incolor.com/bill_r/elf/html/elf-2-39.htm
        Message 3 of 20 , Mar 21, 2013
          --- In cosmacelf@yahoogroups.com, Lee Hart <leeahart@...> wrote:

          >
          > Indeed, it was in one of their original articles.
          >

          I was able to find it. Thanks!
          http://www.incolor.com/bill_r/elf/html/elf-2-39.htm

          >The circuitry needed
          > is little more than the RAM, two diodes, and a pullup resistor on the
          > RAM's "write" pin so it won't accidentally float low.
          >
          > On the Membership Card, I found that I didn't even need the diodes. I
          > could battery backup *everything*, and still hold data for a year on two
          > AA cells.
          >
        • Lee Hart
          ... Indeed, it was in one of their original articles. The circuitry needed is little more than the RAM, two diodes, and a pullup resistor on the RAM s write
          Message 4 of 20 , Mar 21, 2013
            On 3/21/2013 8:06 AM, jdrose_8_bit wrote:
            >> Another option is simply to battery back up your RAM, so it simply
            >> retains the data as long as the batteries last. With CMOS, this can be
            >> many years!

            > That is an interesting option. A CR2032 would probably be enough for a while. I am not much of an EE but I doubt that it would take a complicated circuit change to the PE ELF to do battery backup for the RAM.

            Indeed, it was in one of their original articles. The circuitry needed
            is little more than the RAM, two diodes, and a pullup resistor on the
            RAM's "write" pin so it won't accidentally float low.

            On the Membership Card, I found that I didn't even need the diodes. I
            could battery backup *everything*, and still hold data for a year on two
            AA cells.
            --
            Anyone can make the simple complicated. Creativity is making the
            complicated simple. -- Charles Mingus
            --
            Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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