Atmel Evaluation Kit AT91SAM9M10-G45-EK AT91SAM9M10-G45-EK Data Sheet
Product codes
AT91SAM9M10-G45-EK
88
SAM9M10 [DATASHEET]
6355F–ATARM–12-Mar-13
14.4
Product Dependencies
14.4.1
Power Management
The Real-time Clock is continuously clocked at 32768 Hz. The Power Management Controller has no effect on
RTC behavior.
RTC behavior.
14.4.2
Interrupt
The RTC Interrupt is connected to interrupt source 1 (IRQ1) of the advanced interrupt controller. This interrupt line
is due to the OR-wiring of the system peripheral interrupt lines (System Timer, Real Time Clock, Power Manage-
ment Controller, Memory Controller, etc.). When a system interrupt occurs, the service routine must first determine
the cause of the interrupt. This is done by reading the status registers of the above system peripherals
successively.
is due to the OR-wiring of the system peripheral interrupt lines (System Timer, Real Time Clock, Power Manage-
ment Controller, Memory Controller, etc.). When a system interrupt occurs, the service routine must first determine
the cause of the interrupt. This is done by reading the status registers of the above system peripherals
successively.
14.5
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.
month, date, day, hours, minutes and seconds.
The valid year range is 1900 to 2099, a two-hundred-year Gregorian calendar achieving full Y2K compliance.
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, including year 2000). This is cor-
rect up to the year 2099.
rect up to the year 2099.
After general reset (backup reset), the calendar is initialized to Thursday, January 1, 1998.
14.5.1
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 (idle mode), 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.
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.
14.5.2
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.
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.
14.5.3
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.
• 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.
from minutes to 365/366 days.