M41T82 datasheet(22/64 Pages) STMICROELECTRONICS

Part #	M41T82

Description	Serial I2C bus real-time clock (RTC) with battery switchover

PDF	64 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

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22 / 64 page

Clock operation

M41T82, M41T83

22/64

DocID012578 Rev 19

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)”.

M41T82 Datasheet(PDF) 22 Page - STMicroelectronics