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Real-Time Clock
28.1.2
Features
The RTC module includes:
•
Full clock—days, hours, minutes, seconds
•
Minute countdown timer with interrupt
•
Programmable daily alarm with interrupt
•
Sampling timer with interrupt
•
Once-per-day, once-per-hour, once-per-minute, and once-per-second interrupts
•
Operation determined by reference input oscillator clock frequency and value programmed into
user-accessible registers
— Minimum supported oscillator frequency is 2 Hz
•
Ability to wake the processor from low-power modes (wait, doze, and stop) via the RTC interrupts
28.1.3
Modes of Operation
The real-time-clock operates in various modes as described below:
•
Time-of-day counters
— The clock generation logic divides the reference clock down to 1 Hz using the dividers in the
RTC_GOCU and RTC_GOCL registers.
— The 1 Hz clock increments four counters that are located in three registers
– RTC_SECONDS contains the 6-bit seconds counter
– RTC_HOURMIN contains the 6-bit minutes counter and 5-bit hours counter
– RTC_DAYS contains the 16-bit day counter
•
Alarm
— There are three alarm registers that mirror the three counter registers. An alarm is set by
accessing the real-time clock alarm registers (RTC_ALRM_SEC, RTC_ALRM_HM, and
RTC_ALRM_DAY) and loading the time minus one second that the alarm should generate an
interrupt. When the TOD clock value and the alarm value coincide, one second later an
interrupt occurs.
•
Sampling Timer
— The clock generation logic divides the reference clock down to 512 Hz using the dividers in the
RTC_GOCU and RTC_GOCL registers. The sampling timer generates a periodic interrupt
with frequencies specified by the RTC_IER[SAMn,2HZ] bits. This timer can be used for
digitizer sampling, keyboard debouncing, or communication polling.
examples of the interrupt frequencies of the sampling timer for the possible reference clocks.
Sampling frequencies are dependent upon the RTC oscillator frequency and the value in
RTC_GOC[31:9].
•
Minute Stopwatch
28-2
NOTE
The RTC is enabled during stop mode.
Table 28-15
lists some
Freescale Semiconductor
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