Alpha Servers
Showing results for 
Search instead for 
Did you mean: 

Dallas chip (DS12887)

Honored Contributor

Dallas chip (DS12887)

Anyone here had to replace the Dallas chips in their servers, specifically DS25s, and after how many years in operation?


I have more than a hundred DS25's and since these chips are around 8$, I'm checking if a mass preventive replacement will be justified in the near future.


Thank you

Valued Contributor

Re: Dallas chip (DS12887)



The "Dallas Chip" is manufactured by Dallas Semiconductor (now a division of Maxim Integrated Products as of 2011 ) and is a typical BB_WATCH clock chip used on later-vintage VAX systems and on many of the Alpha systems. The chip provides a lithium battery, a quartz crystal time source, 114 bytes of battery-backed storage, and a mechanism for providing system interrupts for functions such as the interval timer.


The lithium battery used to power the Dallas chip tends to last five to ten years. The battery is not a rechargeable battery. When the battery fails, the chip (a 24-pin DIP package) must be removed from its mounting socket and replaced.

The Dallas part number is DS12887, and sometimes DS1287, DS1287A, or potentially other variants; check the specific box for details. The HP (Compaq, DIGITAL) part for this DS12887 component is the 21-39125-01, usually listed as "Battery, Real Time Clock".


When the battery dies a symptom of an OpenVMS system is to prompt for the date and time at boot.  I believe Tru64 Unix systems report a prepostous time warning on boot.



In my experience the batteries tend to last more that 5 years. Depending on the age of your servers and if you are doing self maintanance having a quantiy of Dallas Chips on hand would be recommended.  The serial number of the DS25 servers can help to determine the age. The Format of the serial number is AAXYY.........   Where AA is the manufacturing location, the X is the Year, ( example 7=2007)  and YY is the Week number of that year. 


I supect many of the DS25 systems were manufactured in the 2005-2007 year range so they would be near the time of predicted end of  battery lifetime. Just a suggestion but maybe start with having 10 spares on hand and see what the failure rate is over the next year or so.  If you start to see many failures then consider being more proactive.  




An employee of HP.