SAM3S8C Atmel Corporation, SAM3S8C Datasheet - Page 246

• Manufacturer Part Number: SAM3S8C
• Manufacturer: Atmel Corporation

14.4
14.4.1
14.4.2
14.4.3
14.4.4
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Functional Description
SAM3S8/SD8
SAM3S8/SD8
Reference Clock
Timing
Alarm
Error Checking
The RTC provides a full binary-coded decimal (BCD) clock that includes century (19/20), year
(with leap years), month, date, day, hours, minutes and seconds.
The valid year range is 1900 to 2099 in Gregorian mode, a two-hundred-year calendar. (Or 1300
to 1499 in Persian mode.)
The RTC can operate in 24-hour mode or in 12-hour mode with an AM/PM indicator.
Corrections for leap years are included (all years divisible by 4 being leap years). This is correct
up to the year 2099.
The reference clock is Slow Clock (SLCK). It can be driven internally or by an external 32.768
kHz crystal.
During low power modes of the processor, the oscillator runs and power consumption is critical.
The crystal selection has to take into account the current consumption for power saving and the
frequency drift due to temperature effect on the circuit for time accuracy.
The RTC is updated in real time at one-second intervals in normal mode for the counters of sec-
onds, at one-minute intervals for the counter of minutes and so on.
Due to the asynchronous operation of the RTC with respect to the rest of the chip, to be certain
that the value read in the RTC registers (century, year, month, date, day, hours, minutes, sec-
onds) are valid and stable, it is necessary to read these registers twice. If the data is the same
both times, then it is valid. Therefore, a minimum of two and a maximum of three accesses are
required.
The RTC has five programmable fields: month, date, hours, minutes and seconds.
Each of these fields can be enabled or disabled to match the alarm condition:
Depending on the combination of fields enabled, a large number of possibilities are available to
the user ranging from minutes to 365/366 days.
Verification on user interface data is performed when accessing the century, year, month, date,
day, hours, minutes, seconds and alarms. A check is performed on illegal BCD entries such as
illegal date of the month with regard to the year and century configured.
If one of the time fields is not correct, the data is not loaded into the register/counter and a flag is
set in the validity register. The user can not reset this flag. It is reset as soon as an acceptable
value is programmed. This avoids any further side effects in the hardware. The same procedure
is done for the alarm.
The following checks are performed:
• If all the fields are enabled, an alarm flag is generated (the corresponding flag is asserted
• If only the “seconds” field is enabled, then an alarm is generated every minute.
and an interrupt generated if enabled) at a given month, date, hour/minute/second.
11090A–ATARM–10-Feb-12
11090A–ATARM–10-Feb-12