Datasheet

DS10198 Rev 8 51/270
STM32L476xx Functional overview
60
3.25 Real-time clock (RTC) and backup registers
The RTC is an independent BCD timer/counter. It supports the following features:
• Calendar with subsecond, seconds, minutes, hours (12 or 24 format), week day, date,
month, year, in BCD (binary-coded decimal) format.
• Automatic correction for 28, 29 (leap year), 30, and 31 days of the month.
• Two programmable alarms.
• On-the-fly correction from 1 to 32767 RTC clock pulses. This can be used to
synchronize it with a master clock.
• Reference clock detection: a more precise second source clock (50 or 60 Hz) can be
used to enhance the calendar precision.
• Digital calibration circuit with 0.95 ppm resolution, to compensate for quartz crystal
inaccuracy.
• Three anti-tamper detection pins with programmable filter.
• Timestamp feature which can be used to save the calendar content. This function can
be triggered by an event on the timestamp pin, or by a tamper event, or by a switch to
VBAT mode.
• 17-bit auto-reload wakeup timer (WUT) for periodic events with programmable
resolution and period.
The RTC and the 32 backup registers are supplied through a switch that takes power either
from the V
DD
supply when present or from the VBAT pin.
The backup registers are 32-bit registers used to store 128 bytes of user application data
when V
DD
power is not present. They are not reset by a system or power reset, or when the
device wakes up from Standby or Shutdown mode.
The RTC clock sources can be:
• A 32.768 kHz external crystal (LSE)
• An external resonator or oscillator (LSE)
• The internal low power RC oscillator (LSI, with typical frequency of 32 kHz)
• The high-speed external clock (HSE) divided by 32.
The RTC is functional in VBAT mode and in all low-power modes when it is clocked by the
LSE. When clocked by the LSI, the RTC is not functional in VBAT mode, but is functional in
all low-power modes except Shutdown mode.
All RTC events (Alarm, WakeUp Timer, Timestamp or Tamper) can generate an interrupt
and wakeup the device from the low-power modes.
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