Hi,
I am seeing a very weird problem when using a DS12C887A RTC chip in my clock application. The issue does not arise when using a DS12C887 chip, which is why this is weird :-(

Here is a description of the problem:

My clock uses an AT89S52 chip. The /IRQ pin of the RTC is connected to the /INT0 pin of the AT89S52.

Now, the clock runs fine. During the time setting mode, when the user can set the time, I disable /INT0 and use only /INT1 to set the time. /INT1 is connected to a tactile switch and is used like a counter to set the value of the time desired by the user.

I have noticed that once the clock goes into the time set mode, the RTC no longer keeps the time. That is, if I abort the time set mode midway and reset the whole system, I lose the time the clock was in time set mode. It is as if, the RTC simply stopped making any updates to the time registers for that period of time when the clock was in time set mode.

If I go ahead and set the time, then it indeed does set the time. Only if I abort the process, I get this scenario.

The weirdest part is that the above does not happen if I use a DS12C887 chip instead of the DS12C887A chip.(Note the extra 'A')

And the DS12C887A chip's backup battery is also fine since, if I turn off the clock, it *does* maintain the time. Which is again very very weird.

In two lines, the problem can be described as:
"DS12C887A does not keep time when clock is in time set mode(when /INT0<->/IRQ is disabled), but keeps time otherwise if turned off completely using the backup power source, built within the RTC.
The above problem does not at all arise if I use a DS12C887 chip."


Can anyone please help me!!
For the moment, I have substituted my DS12C887 chip and resolved the issue. But I would like to know why this is happening!


regards,
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