M41T93_11 STMICROELECTRONICS [STMicroelectronics], M41T93_11 Datasheet - Page 34

• Manufacturer Part Number: M41T93_11
• Description: Serial SPI bus real-time clock with battery switchover
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Clock operation
3.10
3.11
3.12
Note:
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Battery low warning
The M41T93 automatically performs battery voltage monitoring upon power-up and at
factory-programmed time intervals of approximately 24 hours. The battery low (BL) bit, bit
D4 of flags register 0Fh, will be asserted if the battery voltage is found to be less than
approximately 2.5 V. The BL bit will remain asserted until completion of battery replacement
and subsequent battery low monitoring tests, either during the next power-up sequence or
the next scheduled 24-hour interval.
If a battery low is generated during a power-up sequence, this indicates that the battery is
below approximately 2.5 volts and may not be able to maintain data integrity. Clock data
should be considered suspect and verified as correct. A fresh battery should be installed.
If a battery low indication is generated during the 24-hour interval check, this indicates that
the battery is near end of life. However, data is not compromised due to the fact that a
nominal V
battery backup mode, the battery should be replaced.
The M41T93 only monitors the battery when a nominal V
applications which require extensive durations in the battery backup mode should be
powered-up periodically (at least once every few months) in order for this technique to be
beneficial. Additionally, if a battery low is indicated, data integrity should be verified upon
power-up via a checksum or other technique.
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 12.
1. Leap year occurs every four years (for years evenly divisible by four), except for years evenly divisible by
Output driver pin
When the OFIE bit, A1IE bit, and watchdog register are not set to generate an interrupt, the
IRQ/FT/OUT pin becomes an output driver that reflects the contents of D7 of register 08h. In
other words, when D7 (OUT bit) is a '0,' then the IRQ/FT/OUT pin will be driven low.
The IRQ/FT/OUT pin is an open drain which requires an external pull-up resistor.
100. The only exceptions are those years evenly divisible by 400 (the year 2000 was a leap year, year
2100 is not).
CB0
CC
0
0
1
1
Century bits examples
is supplied. In order to insure data integrity during subsequent periods of
Table 12
Doc ID 12615 Rev 6
CB1
0
1
0
1
for additional explanation.
Leap Year?
Yes
No
No
No
CC
is applied to the device. Thus
Example
2000
2100
2200
2300
M41T93
(1)