Loading ...
Sorry, an error occurred while loading the content.

Re: ELF Circuits

Expand Messages
  • sbirdasn
    Also, data/address scrambling is also used to make reverse engineering and copying harder. It won t stop determined efforts, but it slows things down. Can t
    Message 1 of 10 , Mar 31, 2003
    • 0 Attachment
      Also, data/address scrambling is also used to make reverse
      engineering and copying harder. It won't stop determined efforts, but
      it slows things down. Can't just suck the data out of the EPROM
      directly.

      You will also note that vanilla ELF's ignored address bus
      multiplexing because the low order address bits were the ones that
      remained on the bus during the transfer portion of the memory cycle.

      The ELF is a great example of the 1802's ability to minimize logic in
      small systems. Some processor architectures that resorted to
      multiplexing to save pins combined address and data functionality,
      forcing the use of data path wide latches regardless of system size.

      Rearranging the address/data pins sometimes makes troubleshooting a
      bit of a pain at times, especially when the data/address pins are
      arranged on the chip in nice groups. But when the pin arrangement is
      somewhat unorganized to start with, it makes little difference.

      Also, there's really no problem with using negative logic when
      convenient.

      If I recall correctly, ATARI did some funny things with their 400/800
      series disk drive subsystems along the lines of using inverted logic
      data bus disk controller chips. When they low level formatted a disk,
      the empty sectors had $FF's in them instead of the usual $00's. The
      IBM standards for Floppy formatting allow this, but most floppy disk
      technology users didn't stray too far from IBM's default formats for
      what went onto the media. I forget whether the physical media stored
      the user's data bytes logic true or false (relative to IBM) on ATARI
      800 formatted disks. My memory tickles towards negative logic. Since
      it was propriatary, why would ATARI care? It would only make things
      harder for the competition.

      It really doesn't matter what you use for logic assignments as long
      as you are consistent.

      Unless you are fixing/troubleshooting/designing, It's usually at the
      user interface level that matters.

      Tony.
    • J.C.Wren
      I have to laugh. http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3410404139&category=162 [Non-text portions of this message have been removed]
      Message 2 of 10 , Apr 1, 2003
      • 0 Attachment
        I have to laugh.

        http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3410404139&category=162

        [Non-text portions of this message have been removed]
      • sbirdasn
        Yep, That is really funny for those of us in the know as to where they re coming from! Those two VIP s closed out pretty painfully too: $125 for the lone
        Message 3 of 10 , Apr 2, 2003
        • 0 Attachment
          Yep,

          That is really funny for those of us "in the know" as to where
          they're coming from!

          Those two VIP's closed out pretty painfully too: $125 for the lone
          VIP, and $225 for the one with monitor & docs.

          I was tempted to spring for the lone board for say, $25, but that
          would only be for a backup/spare, as I still have my working VIP. The
          feedback did indicate that the lone VIP does work just fine though.

          At least the winning bidders seemed to be happy with their new toys.

          eBay is a strange place.

          Tony.

          --- In cosmacelf@yahoogroups.com, "J.C.Wren" <jcwren@j...> wrote:
          > I have to laugh.
          >
          > http://cgi.ebay.com/ws/eBayISAPI.dll?
          ViewItem&item=3410404139&category=162
          >
        • erd_6502
          ... Well... I paid $35 for my VIP a number of years ago (15?), but it came with several manuals, a full load of RAM and the blue plastic cover (unlike the $125
          Message 4 of 10 , Apr 3, 2003
          • 0 Attachment
            --- In cosmacelf@yahoogroups.com, "sbirdasn" <sbirdasn@y...> wrote:
            > Those two VIP's closed out pretty painfully too: $125 for the lone
            > VIP, and $225 for the one with monitor & docs.
            >
            > I was tempted to spring for the lone board for say, $25, but that
            > would only be for a backup/spare, as I still have my working VIP.

            Well... I paid $35 for my VIP a number of years ago (15?), but
            it came with several manuals, a full load of RAM and the blue
            plastic cover (unlike the $125 bare VIP), so I'd be surprised
            (and pleased!) to get one for even $50 these days.

            -ethan
          Your message has been successfully submitted and would be delivered to recipients shortly.