M41T62 datasheet(28/40 Pages) STMICROELECTRONICS

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Clock operation

M41T62/63/64/65

28/40

3.8

Century bits

These two bits will increment in a binary fashion at the turn of the century, and handle all

leap years correctly. See Table 10 on page 29 for additional explanation.

3.9

Output driver pin (M41T62/65)

When the OFIE Bit, AFE Bit, and watchdog register are not set to generate an interrupt, the

IRQ/OUT pin becomes an output driver that reflects the contents of D7 of the Calibration

Note:

The IRQ/OUT pin is an open drain which requires an external pull-up resistor.

3.10

Oscillator stop 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:

●

The first time power is applied (defaults to a '1' on power-up).

Note:

If the OF Bit cannot be written to '1' four (4) seconds after the initial power-up, the STOP Bit

(ST) should be written to a '1,' then immediately reset to '0.'

●

The voltage present on VCC or battery is insufficient to support oscillation.

●

The ST Bit is set to '1.'

●

External interference of the crystal

If the Oscillator Fail Interrupt Enable Bit (OFIE) is set to a '1,' the IRQ pin will also be

activated. The IRQ 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.

3.11

Initial power-on defaults

Upon application of power to the device, the register bits will initially power-on in the state

indicated in Table 9.

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