STFPC320 STMicroelectronics, STFPC320 Datasheet - Page 28

• Manufacturer Part Number: STFPC320
• Description: Front Panel Controller/driver With Standby Power Management And Real-time Clock
• Manufacturer: STMicroelectronics

Real Time Clock (RTC) operation
6.9
6.10
Note:
28/75
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 6.
1.
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 data. 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 a ‘0’. This will restart the
oscillator.
The following conditions can cause the OF bit to be set:
●
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 a ‘0’.
●
●
●
If the oscillator Fail Interrupt Enable Bit (OFIE) is set to a ‘1’, the IRQ_N/SQW pin will also
be activated. The IRQ_N/SQW 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 the power-down condition, this bit will be set correctly.
100. The only exceptions are those years evenly divisible by400 (the year 2000 was a leap year, year 2100
is not).
Leap year occurs every four years (for years evenly divisible by 4), except for years evenly divisible by
The first time power is applied (defaults to a ‘1’ on power-up).
The voltage present on Vcc is insufficient to support oscillation.
The ST Bit is set to a ‘1’.
External interference of the crystal
CB1
0
0
1
1
Century bits
Table 6
CB0
below for additional explanation.
0
1
0
1
Leap Year?
Yes
No
No
No
Example
2000
2100
2200
2300
STFPC320
(1)