13/23

M41T60

Century Bits

These two bits will increment in a binary fashion at

the turn of the century, and handle leap years cor-

rectly. See Table 3 for additional explanation.

Output Driver Pin

When the OFIE Bit is not set to generate an inter-

rupt, the OFIRQ/OUT pin becomes an output driv-

er 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.

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

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 oscil-

lator restarts.

The oscillator must start and have run for at least

4 seconds before attempting to set the OFIE Bit to

'1.'

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.

Table 3. 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).

CB0

CB1

Leap Year?

0

0

Yes

2000

0

1

No

2100

1

0

No

2200

1

1

No

2300