New Life for an old DS1287 repudiated. This page is thankfully mirrored from Daniel Savel's web page.

This is a CI which was used a lot before year 2000 . It was used to generate the time on our venerable computers.

Further more, its non-volatil RAM kept the BIOS data memorized (about 50 bytes).

Inside this circuit, there is a lithium battery. This battery enables the clock to run alone during about 10 years without external power.


 I collected two of these circuits, I was sure they were still running… Unfortunately the two batteries were empty :

my Z80-Forth card lost the time each time the power of system was off !

I decided then, to "explode" one circuit to see if it was possible to change the battery (an equivalent circuit costs about 2 to 30 Euros).


You can see the battery, the quartz and the original circuit DS1285.



After the smoke has left, :o) I discovered that the base of the DS1287 was in fact a DS1285 circuit where Mr Dallas had glued a little battery . Some pins were folded inside the cover for the connections.

No problem : I only needed to cut the old battery and solder the new one.

The pictures tell more than a long speech !


After the dissection

If you plan to try this operation, look at the photos and locate the spot where you will cut the cover. Reduce slowly the resin around the battery until the metal raises. Look for the connections of the battery and the pin of the CI. Cut them and solder a new battery.


(This is a delicate work, try to drink a little of French white win if you are trembling !)


If you plan to use this CI, you first need to write the 25h value in 0Ah register of the chip. I also advice to write the 06h value in the 0Bh register.

Using this chip is very easy; all you need is to read or write in the memory. Hour is at 04h, minute at 02h, second at 00h. The year is at 09h. It contains the value 02 for year 2002 (where is the 2k bug ??)


It is terminated. Now, I've the time during 200 years … 


Sheets of the circuits : DS1285 DS1287


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