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Thread: Are Dallas DS12887A & DS12887+ interchangeable?

  1. #1
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    Default Are Dallas DS12887A & DS12887+ interchangeable?

    I've just replaced the Dallas chip on my clone P166 board. The original was a DS12887A. Last time it failed about 4/5 years ago I was able to get a NOS DS12887A.

    However rather than hunt down another DS12887A just to find it has a flat battery this time I have replaced it instead with a DS12887+ was is a new part (well made in 2016 anyway).

    AIUI the '+' just means the part is lead free for ROHS compliance and all the 'A' meant on the original chip was it supported RAM reset which was only useful for things like re-accessing the BIOS when a password had been set and forgotten etc.

    The system will run with the new chip but it still reports a dead CMOS battery. I'm hoping it's just a bad chip, but is there any known compatibility issue between the two chips?

  2. #2
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    Dunno--but I generally prefer reworking old DS1287 chips to retain absolute compatibility. Glitch (IIRC) also offers some replacements that are not encapsulated.

  3. #3
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    If the DS12887 is a new part, you may need to start the oscillator...

    "When the DS12887, DS12887A, DS12C887, and DS12C887A are shipped from the factory, the internal oscillator is turned off. This prevents the lithium energy cell from being used until the device is installed in a
    system. A pattern of 010 in bits 4 to 6 of Register A turns the oscillator on and enables the countdown chain. A pattern of 11x (DV2 = 1, DV1 = 1, DV0 = X) turns the oscillator on, but holds the countdown chain of the oscillator in reset. All other combinations of bits 4 to 6 keep the oscillator off."

    - Gary

  4. #4
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    Quote Originally Posted by Chuck(G) View Post
    Dunno--but I generally prefer reworking old DS1287 chips to retain absolute compatibility. Glitch (IIRC) also offers some replacements that are not encapsulated.
    I sure do!

    https://www.tindie.com/products/glit...cement-module/ <- full replacement for the 12887
    https://www.tindie.com/products/glit...-ds12887-rtcs/ <- just the repair board for DIY rebuilding

    Where did you get your replacement DS12887+ from? Every Chinese eBay seller I've bought from has sent renumbered parts with at least partially drained batteries, if not totally dead -- for MK48Txx series NVRAMs anyway, I've never bought used DS12887s from eBay since I can still get the DS12885 (the IC that's in a 12887) from Mouser.

  5. #5

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    I had to replace my Dallas DS12887A chip in Dec 2015 in my Acer Acros from 1995.
    I ordered a replacement DS12887A+ from Digi-Key for $10:
    https://www.digikey.com/product-deta...+/DS12887A+-ND

    The replacement chip had a code date of 1505GF, so was less than 6 months old.
    This was a direct replacement and works great. PC fired right up with no CMOS errors.
    Still no issues after three years.

  6. #6
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    Quote Originally Posted by glitch View Post
    I sure do!

    https://www.tindie.com/products/glit...cement-module/ <- full replacement for the 12887
    https://www.tindie.com/products/glit...-ds12887-rtcs/ <- just the repair board for DIY rebuilding

    Where did you get your replacement DS12887+ from? Every Chinese eBay seller I've bought from has sent renumbered parts with at least partially drained batteries, if not totally dead -- for MK48Txx series NVRAMs anyway, I've never bought used DS12887s from eBay since I can still get the DS12885 (the IC that's in a 12887) from Mouser.
    It was from a UK ebay seller but I suspect they are just a reseller of Chinese parts. Sent it straight back, found another NOS DS12887A from a UK seller. This one was made in 2011 but it does work perfectly...for now anyway.

  7. #7
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    Really, once you've either used one of Glitch's setups or modified a dead Dallas chip with a coin cell holder on top, you don't need to worry about things again.

  8. #8

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    Quote Originally Posted by Chuck(G) View Post
    ...modified a dead Dallas chip with a coin cell holder...
    This is my favourite. keep the aesthetic and you can put the battery on long thin/hidden leads to stuff it out of harm's way.

  9. #9
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    Quote Originally Posted by EkriirkE View Post
    This is my favourite. keep the aesthetic and you can put the battery on long thin/hidden leads to stuff it out of harm's way.
    I am now going to try a mod on the old chip. I don't want to keep replacing the chip all the time and reliable working ones seem to be scarce.

    Is it viable to mod a chip in place? This system has a socketed chip but I have another computer with a dead Dallas chip which currently is unbootable because of it and unfortunately the chip is soldered in. Would be nice to be able to mod it without having to get it out of the board first.

  10. #10
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    Yup, I did a mod recently to a 80286 board with a bunch of SMT stuff that I really didn't want to disturb. FWIW, I don't use a Dremel, but rather a Foredom handset, which has much finer control. If you've got a "naked" 24-pin DIP kicking around, you can use it to "spot" the appropriate pin positions from the top of the DS1287.

    For some strange reason, the coin-cell holder didn't want to stick to the top of the DS1287 when using 5-minute epoxy. I resorted to polyurethane ("Gorilla") glue to do the job.

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