Atmel Evaluation Kit AT91SAM9X25-EK AT91SAM9X25-EK Data Sheet
Product codes
AT91SAM9X25-EK
120
SAM9X25 [DATASHEET]
11054E–ATARM–10-Mar-2014
15.4 Product Dependencies
15.4.1 Power Management
The Real-time Clock is continuously clocked at 32768 Hz. The Power Management Controller has no effect on RTC
behavior.
behavior.
15.4.2 Interrupt
Within the System Controller, the RTC interrupt is OR-wired with all the other module interrupts.
Only one System Controller interrupt line is connected on one of the internal sources of the interrupt controller.
RTC interrupt requires the interrupt controller to be programmed first.
When a System Controller interrupt occurs, the service routine must first determine the cause of the interrupt. This is
done by reading each status register of the System Controller peripherals successively.
done by reading each status register of the System Controller peripherals successively.
15.5 Functional Description
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.
date, day, hours, minutes and seconds.
The valid year range is 1900 to 2099 in Gregorian mode, a two-hundred-year calendar.
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.
15.5.1 Reference Clock
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.
to take into account the current consumption for power saving and the frequency drift due to temperature effect on the
circuit for time accuracy.
15.5.2 Timing
The RTC is updated in real time at one-second intervals in normal mode for the counters of seconds, at one-minute
intervals for the counter of minutes and so on.
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, seconds) 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.
RTC registers (century, year, month, date, day, hours, minutes, seconds) 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.
15.5.3 Alarm
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:
If all the fields are enabled, an alarm flag is generated (the corresponding flag is asserted and an interrupt
generated if enabled) at a given month, date, hour/minute/second.
generated if enabled) at a given month, date, hour/minute/second.
If only the “seconds” field is enabled, then an alarm is generated every minute.
Depending on the combination of fields enabled, a large number of possibilities are available to the user ranging from
minutes to 365/366 days.
minutes to 365/366 days.