23/33

M41T62/63/64/65

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., page 23 for additional

explanation.

Output Driver Pin (M41T62/65)

When the OFIE Bit, AFE Bit, and watchdog regis-

ter are not set to generate an interrupt, the IRQ/

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 IRQ/

OUT pin will be driven low.

Note: The IRQ/OUT pin is an open drain which re-

quires an external pull-up resistor.

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 da-

ta. 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.'

–

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.

Initial Power-on Defaults

Upon application of power to the device, the regis-

ter bits will initially power-on in the state indicated

in Table 9.

Table 9. Initial Power-on Default Values

Note: 1. All other control bits power-up in an undetermined state.

Table 10. Century Bits Examples

Note: 1. Leap year occurs every four years (for years evenly divisible by four), except for years evenly divisible by 100. The only exceptions

are those years evenly divisible by 400 (the year 2000 was a leap year, year 2100 is not).

Condition

Device

ST

OF

OFIE

OUT

FT

AFE

SQWE

32KE

RS3-1

RS0

Watchdog

Initial

M41T62

0

1

0

1

N/A

0

1

N/A

0

1

0

M41T63

0

1

N/A

N/A

N/A

N/A

1

N/A

0

1

0

M41T64

0

1

N/A

N/A

N/A

N/A

0

1

0

1

0

M41T65

0

1

0

1

0

0

N/A

N/A

N/A

N/A

0

CB0

CB1

Leap Year?

00

Yes

2000

0

1

No

2100

1

0

No

2200

1

1

No

2300