STM32L552CET6PTR datasheet(71/340 Pages) STMICROELECTRONICS

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DS12737 Rev 6

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STM32L552xx

Functional overview

3.31

Real-time clock (RTC)

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.

•

TrustZone support:

–

RTC fully securable

–

Alarm A, alarm B, wakeup Timer and timestamp individual secure or non-secure

configuration

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 a prescaler in the RCC.

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.

3.32

Tamper and backup registers (TAMP)

32 32-bit backup registers are 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. 8 tamper pins and 7 internal tampers are available for anti-tamper

detection.

The external tamper pins can be configured for edge detection, or level detection with or

without filtering, or active tamper which increases the security level by auto checking that

the tamper pins are not externally opened or shorted.

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