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SAM G51 [DATASHEET]
11209C–ATARM–20-Dec-13
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.
Hour, minute and second matching alarm (SECEN, MINEN, HOUREN) can be enabled independently of SEC, MIN,
HOUR fields.
Note:
To change one of the SEC, MIN, HOUR, DATE, MONTH fields, it is recommended to disable the field before
changing the value and then re-enable it after the change has been made. This requires up to three accesses to
the RTC_TIMALR or RTC_CALALR. The first access clears the enable corresponding to the field to change
(SECEN, MINEN, HOUREn, DATEEN, MTHEN). If the field is already cleared, this access is not required. The
second access performs the change of the value (SEC, MIN, HOUR, DATE, MONTH). The third access is
required to re-enable the field by writing 1 in SECEN, MINEN, HOUREn, DATEEN, MTHEN fields.
14.5.4 Error Checking when Programming
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 followed for the alarm.
The following checks are performed:
1.
Century (check if it is in range 19–20 or 13–14 in Persian mode)
2.
Year (BCD entry check)
3.
Date (check range 01–31)
4.
Month (check if it is in BCD range 01–12, check validity regarding “date”)
5.
Day (check range 1–7)
6.
Hour (BCD checks: in 24-hour mode, check range 00–23 and check that AM/PM flag is not set if RTC is set in 24-
hour mode; in 12-hour mode check range 01–12)
7.
Minute (check BCD and range 00–59)
8.
Second (check BCD and range 00–59)
Note:
If the 12-hour mode is selected by means of the RTC_MR, a 12-hour value can be programmed and the
returned value on RTC_TIMR will be the corresponding 24-hour value. The entry control checks the value of the
AM/PM indicator (bit 22 of RTC_TIMR) to determine the range to be checked.
14.5.5 RTC Internal Free Running Counter Error Checking
To improve the reliability and security of the RTC, a permanent check is performed on the internal free running counters
to report non-BCD or invalid date/time values.
An error is reported by TDERR bit in the status register (RTC_SR) if an incorrect value has been detected. The flag can
be cleared by programming the TDERRCLR in the RTC status clear control register (RTC_SCCR).
Anyway the TDERR error flag will be set again if the source of the error has not been cleared before clearing the TDERR
flag. The clearing of the source of such error can be done either by reprogramming a correct value on RTC_CALR and/or
RTC_TIMR.