32G474 datasheet(39/236 Pages) STMICROELECTRONICS

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DS12288 Rev 4

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STM32G474xB STM32G474xC STM32G474xE

Functional overview

3.25

Real-time clock (RTC) and backup registers

The RTC 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.

•

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 is supplied through a switch that takes power either from the VDD supply when

present or from the VBAT pin.

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) can generate an interrupt and wakeup

the device from the low-power modes.

3.26

Tamper and backup registers (TAMP)

•

32 32-bit backup registers, retained in all low-power modes and also in VBAT mode.

They can be used to store sensitive data as their content is protected by an tamper

detection circuit. They are not reset by a system or power reset, or when the device

wakes up from Standby or Shutdown mode.

•

Up to three tamper pins for external tamper detection events. The external tamper pins

can be configured for edge detection, edge and level, level detection with filtering.

•

Five internal tampers events.

•

Any tamper detection can generate a RTC timestamp event.

•

Any tamper detection erases the backup registers.

•

Any tamper detection can generate an interrupt and wake-up the device from all low-

power modes.

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