STM32L433CB datasheet(47/225 Pages) STMICROELECTRONICS

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DS11449 Rev 5

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STM32L433xx

Functional overview

3.24

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 VDD 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 VDD 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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