ST STM32F301 6 Series Reference Manual page 610

Real-time clock (RTC)
register (RTC_ISR)). The copy is not performed in Stop and Standby mode. When exiting
these modes, the shadow registers are updated after up to 1 RTCCLK period.
When the application reads the calendar registers, it accesses the content of the shadow
registers. It is possible to make a direct access to the calendar registers by setting the
BYPSHAD control bit in the RTC_CR register. By default, this bit is cleared, and the user
accesses the shadow registers.
When reading the RTC_SSR, RTC_TR or RTC_DR registers in BYPSHAD=0 mode, the
frequency of the APB clock (f
(f
RTCCLK
The shadow registers are reset by system reset.
24.3.5 Programmable alarms
The RTC unit provides programmable alarm: Alarm A and Alarm B. The description below is
given for Alarm A, but can be translated in the same way for Alarm B.
The programmable alarm function is enabled through the ALRAE bit in the RTC_CR
register. The ALRAF is set to 1 if the calendar subseconds, seconds, minutes, hours, date
or day match the values programmed in the alarm registers RTC_ALRMASSR and
RTC_ALRMAR. Each calendar field can be independently selected through the MSKx bits
of the RTC_ALRMAR register, and through the MASKSSx bits of the RTC_ALRMASSR
register. The alarm interrupt is enabled through the ALRAIE bit in the RTC_CR register.
Caution: If the seconds field is selected (MSK1 bit reset in RTC_ALRMAR), the synchronous
prescaler division factor set in the RTC_PRER register must be at least 3 to ensure correct
behavior.
Alarm A and Alarm B (if enabled by bits OSEL[1:0] in RTC_CR register) can be routed to the
RTC_ALARM output. RTC_ALARM output polarity can be configured through bit POL the
RTC_CR register.
24.3.6 Periodic auto-wake-up
The periodic wake-up flag is generated by a 16-bit programmable auto-reload down-
counter. The wake-up timer range can be extended to 17 bits.
The wake-up function is enabled through the WUTE bit in the RTC_CR register.
The wake-up timer clock input can be:
• RTC clock (RTCCLK) divided by 2, 4, 8, or 16.
When RTCCLK is LSE(32.768 kHz), this allows to configure the wake-up interrupt
period from 122 µs to 32 s, with a resolution down to 61 µs.
•
ck_spre (usually 1 Hz internal clock)
When ck_spre frequency is 1Hz, this allows to achieve a wake-up time from 1 s to
around 36 hours with one-second resolution. This large programmable time range is
divided in 2 parts:
–
–
610/874
APB
).
from 1s to 18 hours when WUCKSEL [2:1] = 10
and from around 18h to 36h when WUCKSEL[2:1] = 11. In this last case 2
added to the 16-bit counter current value.When the initialization sequence is
complete (see Programming the wake-up timer on page
counting down.When the wake-up function is enabled, the down-counting remains
active in low-power modes. In addition, when it reaches 0, the WUTF flag is set in
) must be at least 7 times the frequency of the RTC clock
RM0366 Rev 5
RM0366
is
16
612), the timer starts