m41t93 STMicroelectronics, m41t93 Datasheet - Page 34

• Manufacturer Part Number: m41t93
• Description: Serial Spi Bus Rtc With Battery Switchover
• Manufacturer: STMicroelectronics

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Oscillator fail detection
If the Oscillator Fail (OF) Bit is internally set to a '1,' this indicates that the oscillator has
either stopped, or was stopped for some period of time and can be used to judge the validity
of the clock and date data. This bit will be set to '1' any time the oscillator stops.
In the event the OF Bit is found to be set to '1' at any time other than the initial power-up, the
STOP Bit (ST) should be written to a '1,' then immediately reset to '0.' This will restart the
oscillator. The following conditions can cause the OF Bit to be set:
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If the OF Bit cannot be written to '1' four seconds after the initial power-up, the STOP Bit
(ST) should be written to a '1,' then immediately reset to '0.'
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For the M41T93, if the Oscillator Fail Interrupt Enable Bit (OFIE) is set to a '1,' the
IRQ/FT/OUT pin will also be activated. The IRQ/FT/OUT output is cleared by resetting the
OFIE or OF Bit to '0' (NOT by reading the Flag Register).
The OF Bit will remain set to '1' until written to logic '0.' The oscillator must start and have
run for at least 4 seconds before attempting to reset the OF Bit to '0.' If the trigger event
occurs during a power down condition, this bit will be set correctly.
Oscillator fail interrupt enable
If the Oscillator Fail Interrupt Bit (OFIE) is set to a '1,' the IRQ/FT/OUT pin will also be
activated. The IRQ/FT/OUT output is cleared by resetting the OFIE or OF Bit to '0' (not be
reading the Flags Register).
The first time power is applied (defaults to a '1' on power-up).
The voltage present on V
The ST Bit is set to '1.'
External interference of the crystal
CC
or battery is insufficient to support oscillation.