M41T60

Clock operation

13/24

Figure 12. Calibration waveform

3.2

Century bits

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

years correctly. See Table 3 on page 14 for additional explanation.

3.3

Output driver pin

When the OFIE Bit is not set to generate an interrupt, the OFIRQ/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 OFIRQ/OUT pin will be driven low.

Note:

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

3.4

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.

conditions 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

oscillator restarts.

The oscillator must start and have run for at least 4 seconds before attempting to set the

OFIE Bit to '1.'

AI00594B

NORMAL

POSITIVE

CALIBRATION

NEGATIVE

CALIBRATION