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A real question about EEPROM vs. Flash

Discussion in 'Electronic Design' started by Rich Grise, Jul 22, 2005.

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  1. Rich Grise

    Rich Grise Guest

    So, I'm bidding this ultra-sweet project, and I'm studying the
    data sheet of the PIC18F6520/8520/6620/8620/6720/8720, and it
    says, Flash: 100,000 cycles, EEPROM: 1,000,000 cycles. What
    are the other differences? Is flash cheaper than EEPROM? I
    have noticed that it tends to get used for program memory,
    and EEPROM for data, but are there any other differences,
    like, maybe program/cycle time, erase modes, that sort of
    thing?

    Thanks,
    Rich
     
  2. Bozzion

    Bozzion Guest

    yes, it is on the data sheets
     
  3. Andy Peters

    Andy Peters Guest

    Betcha you can only do page or block erase for the Flash, but you
    should be able to erase and write to single bytes in the EEPROM.

    If I wasn't lazy, I'd look that up on the data sheet to be sure.

    -a
     
  4. Svilen

    Svilen Guest

    A lot of differencies, starting from the physical effect. Flash is based
    on the effect of hot electrons (if I remember correctly) and by nature
    it is a descructive effect, that is not the case with the EEPROM. Flash
    basic cell is much smaller that the EEPROM one, however the periphery is
    much much bigger, that's why the chips are cost effective for big amount
    of memory. With EEPROM should be the opposite.
    The other big difference is the erase/write time - much shorter(faster)
    for the flash, but always on blocks - i.e. a single cell can't be
    erased/programed. This is not a limitation for the EEPROM, but the
    write/erase time is is much slower.

    Hope this helps
    Svilen
     
  5. Rich Grise

    Rich Grise Guest

    Yes, considerably!

    :)
    Thanks!
    Rich
     
  6. Bob Monsen

    Bob Monsen Guest

    Many of the low end PICs can't write their own flash. Thus, EEPROM is
    the only non-volatile storage for them.

    Flash usually starts out as 1s, and can be set to 0s. Erased flash thus
    contains FF. Erasing can usually only be done on a page basis, and takes
    a long time.

    --
    Regards,
    Bob Monsen

    If a little knowledge is dangerous, where is the man who has
    so much as to be out of danger?
    Thomas Henry Huxley, 1877
     
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