Datasheet

DocID10396 Rev 14 17/28
M41T60 Clock operation
3.3 Leap year
Leap year occurs every four years, in years which are multiples of 4. For example, 2012
was a leap year. An exception to that is any year which is a multiple of 100. For example,
the year 2100 is not a leap year. A further exception is that years which are multiples of 400
are indeed leap years. Hence, while 2100 is not a leap year, 2400 is.
During any year which is a multiple of 4, the M41T6x RTC will automatically insert leap day,
February 29. Therefore, the application software must correct for this during the exception
years (2100, 2200, etc.) as noted above.
3.4 Output driver pin
When the OFIE bit is not set to generate an interrupt, the OFIRQ/OUT pin becomes an
output driver that reflects the contents of D7 of the calibration register. In other words, when
D7 (OUT bit) is a '0,' then the OFIRQ
/OUT pin will be driven low.
Note: The OFIRQ
/OUT pin is an open drain which requires an external pull-up resistor.
3.5 Oscillator stop detection
In the event that the oscillator has either stopped, or was stopped for some period of time,
and if the oscillator fail interrupt enable (OFIE) bit is set to a '1,' an interrupt will be
generated. This interrupt can be used to judge the validity of the clock and date data.
The interrupt will be active any time the oscillator stops while V
CC
is ≥ 1.0V. The following
conditions will cause the OFIRQ
pin to be active:
• the ST bit is set to '1.'
• external interference or removal of the crystal.
The oscillator fail interrupt (OFIRQ
) will remain active until the OFIE bit is reset to '0,' or the
oscillator restarts.
The oscillator must start and have run for at least 4 seconds before attempting to set the
OFIE bit to '1.'
3.6 Initial power-on defaults
Upon initial application of power to the device, the OUT bit will be set to a '1,' while the ST,
OFIE, and FT bits will be set to '0.' All other register bits will initially power-on in a random
state.