Datasheet

Clock operation M41T82, M41T83
22/64 DocID012578 Rev 16
3.2.1 Power-down time-stamp
Some applications may need to determine the amount of time spent in backup mode. That
can be calculated if the time of power-down and the time of power-up are known. The latter
is straightforward to obtain. But the time of power-down is only available if an access
occurred just prior to power-down. That is, if there was an access of the device just prior to
power-down, the time of the access would have been frozen in the buffer transfer registers
and thus the approximate time of power-down could be obtained.
If an application requires the time of power-down, the best way to implement it is to set up
the software to do frequent reads of the clock, such as once every 1 or 5 seconds. That
way, at power-up, the buffer-transfer registers will contain a time value within 1 (or 5)
seconds of the actual time of power-down. For more information, please refer to AN1572,
“Power-down time-stamp function in serial real-time clocks (RTCs)”.