A time-of-day alarm, three maskable interrupts with a common interrupt output, and a programmable squarewave output are available. A precision temperature-compensated circuit monitors the status of VCC. If a primary power-supply failure is detected, the devices automatically switch to a backup supply. The backup supply input supports a primary battery, such as lithium coin cell. The oscillator circuit does not require any external resistors or capacitors to operate.
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The usual reason for these errors is a flat CMOS battery. In most machines this problem is easily rectified, simply requiring an over-the-counter 3 to 6v battery replacement on the motherboard.
However the process is not always quite so hassle-free. Along with the real time clock this chip also holds the CMOS battery, all entombed together in a compact plugin unit. Rather neat perhaps, until the battery goes flat in which case the whole chip needs to be replaced!
That is assuming you can get the part in the first place. Not easy when dealing with a computer over 20 years old. Every time I booted up the machine, I was greeted with the errors above. I needed to do something about it!
Almost immediately I found an article written by someone who had the same issue and had published a solution. It involved hacking away parts of the chip, then rewiring an external battery onto it. Following the web article I hacked away the chip material with a small serrated knife.
I found the substrate quite soft and easy to cut into. Photo 2. Exposing the contacts inside the DS chip After these pins were exposed, breaking the connection to the internal battery was easy. All that remained then was to simply wire up a button battery holder to the exposed metal. My hack job can be seen below.
Photo 3. Dallas chip with new external battery After making sure the solder was firmly connected it was a matter of inserting a 3v lithium button battery into the holder photo 3 , replacing the chip on the board and screwing the PC cover back on.
Photo 4. No errors, just a straight boot-through as it should be. All in all, the repair took about a hour and was pretty straightforward. All power to the Internet and particular thanks to Peter.
Wendt who wrote up the procedure.
DS12887 - DS12887 Real Time Clock Datasheet