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EEPROM or NVSRAM

Discussion in 'Electronic Design' started by mpm, Jun 7, 2007.

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  1. mpm

    mpm Guest

    A project I'm working on will likely go into the 1,000's of units.
    The design calls for an 8051 and a RTC.

    I was planning to use the DS1307 because I'm familiar with it, it fits
    the bill, and I already have the code for it. Plus, it's pretty
    bullet-proof.

    And even though we've used it in lots of prior projects, we never
    really had a need to use the skimpy 56 bytes of NV-SRAM it provides.

    This project happens to be a candidate. If these bytes didn't exist,
    we'd probably just select a micro with EEPROM and that'd be it, or use
    an outboard serial EEPROM. (This app does not require so many writes
    as to wear out an EEPROM. We're just storing some options variables,
    that the user can modify on initial installation.)

    So my question: Is there any reason we shouldn't use the DS1307
    registers for long-term, unattended memory storage? Anybody doing
    this now? And having good results? I would really like to save the $
    $ on the less-capable 8051's. (i.e., without EEPROM capability).

    We're decided on a CR2032 coin cell, and the 106K holder from Keystone
    (which is a FANTASTIC holder for this battery! Nice and tight!) The
    battery should last for many years, and it's not a problem if the
    memory dumps when replacing the cell.

    The application will be inside a work truck, permanently attached, so
    bumps and bruises are expected... I should also mention that even if
    the memory is lost, the device will still work, but will do so in a
    factory-default sort of way - which will likely not be that
    objectionable to the customer.(?)

    Anybody have any thoughts about EEPROM vs. NV-SRAM or does it really
    make any difference?
     
  2. Rich Grise

    Rich Grise Guest

    Well, this part is a little confusing - if you're saying that the uP
    without the EEPROM is cheaper than the one with, and you've already
    climbed the learning cliff on the DS part, I'd say do it the way you
    know.

    Before there was flash/eeprom, that's what they did in PCs for some
    time.

    I once made $60.00 telling a client that their Compaq battery was dead. :)

    Cheers!
    Rich
     
  3. mpm

    mpm Guest

    Micros with EEPROM capability are bit more rare & expensive.
    I'm talking about data storage, not program storage. (But I guess
    there are some Flash micro's out there that give you in-application
    byte-level programming access to the array too. I hadn't even
    considered that - and probably wouldn't.)

    I guess when you boil it down, it's the "S" in NV-SRAM that's giving
    me pause.

    It just doesn't sound "reliably permanent", but I guess it keeps time
    OK, and it's the same basic memory array, so maybe I shouldn't have
    heart palpatiation over it??...
     
  4. Rich Grise

    Rich Grise Guest

    AFAIK, "SRAM" means "static RAM". So it will be permanent as long as the
    battery holds up. And if you're finicky about maintaining it while
    changing out the battery, a BMF cap should do it.

    Good Luck!
    Rich
     
  5. Jasen

    Jasen Guest

    Isn't that exactly what the IBM PC/AT did ?
    every time the battery goes flat the configuration goes south.
    will that be an issue?

    Bye.
    Jasen
     
  6. mpm

    mpm Guest

    Thanks guys.

    After researching this a bit more, and sleeping on it.....

    I'm just going to go with storing the user data in the DS1307
    registers.
    It's the cheapest approach, and the damage done if the data gets lost
    or corrupted in insignificant. And the battery change problem isn't a
    deal-breaker.

    Last couple years I guess was on this flash bandwagon and forgot how
    to jump off.....
    You start thinking of "static" in terms of minutes, not years.

    -mpm
     
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