M41T82 datasheet(42/58 Pages) STMICROELECTRONICS

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Clock operation

M41T82 M41T83

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3.13

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. This bit 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' 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

For the M41T83, if the Oscillator Fail Interrupt Enable bit (OFIE) is set to a '1,' the

IRQ1/FT/OUT pin will also be activated. The IRQ1/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.

3.14

Oscillator fail interrupt enable (M41T83 only)

If the Oscillator Fail Interrupt Enable bit (OFIE) is set to a '1,' the IRQ1/FT/OUT pin will also

be activated. The IRQ1/FT/OUT output is cleared by resetting the OFIE or OF bit to '0' (not

by reading the Flags Register).

3.15

Initial power-on defaults

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

state indicated in Table 15 and Table 16.

Table 15.

Initial power-on default values (part 1)

Condition(1)

All other control bits power-up in an undetermined state.

CB1 CB0 OUT

DCS

ACS

Digital

calib.

Analog

calib.

OFIE

(2)

M41T83 only.

Watchdog

(3)

BMB0-BMB4, RB0, RB1.

A1IE

(2)

SQWE

(2)

ABE

Initial

Power-up

Subsequent

Power-up(4) (5)

With battery back-up.

UC = unchanged.

M41T82 Datasheet(PDF) 42 Page - STMicroelectronics

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