33/42

M41ST87Y, M41ST87W

Electronic Serial Number

The M41ST87Y/W has a unique 8-Byte lasered,

serial number with parity. This serial number is

“Read only” and is generated such that no two de-

vices will contain an identical number.

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. The following conditions can cause the OF

Bit to be set:

– The first time power is applied (defaults to a '1'

on power-up).

cient to support oscillation.

– The ST Bit is set to '1.'

If the Oscillator Fail Interrupt Enable Bit (OFIE) is

set to a '1,' the IRQ/OUT pin will also be activated.

The IRQ/OUT output is cleared by resetting the

OF Bit to '0,' resetting the OFIE Bit to '0,' or the

RST output is enabled (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.' This function operates both under normal

power and in battery back-up. If the trigger event

occurs during a power-down condition, this bit will

be set correctly.

Note: The ABE Bit must be set to '1' for the IRQ/

OUT pin to be activated in battery back-up.

Initial Power-on Defaults

See Table 13., page 34.

Table 11. 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).

Note: 1. Default Setting

CB0

CB1

Leap Year?

00

Yes

2000

0

1

No

2100

1

0

No

2200

1

1

No

2300

STOP Bit (ST)

Units

Min

Max

00

96

ms

0

1

40

200

ms

1

X

50

2000

µs