STM32F051R6 datasheet(22/104 Pages) STMICROELECTRONICS

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Functional overview

STM32F051x

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Doc ID 022265 Rev 3

operates independently from the main clock, it can operate in Stop and Standby modes. It

can be used either as a watchdog to reset the device when a problem occurs, or as a free

running timer for application timeout management. It is hardware or software configurable

through the option bytes. The counter can be frozen in debug mode.

3.14.5

System window watchdog (WWDG)

The system window watchdog is based on a 7-bit downcounter that can be set as free

running. It can be used as a watchdog to reset the device when a problem occurs. It is

clocked from the APB clock (PCLK). It has an early warning interrupt capability and the

counter can be frozen in debug mode.

3.14.6

SysTick timer

This timer is dedicated to real-time operating systems, but could also be used as a standard

down counter. It features:

●

A 24-bit down counter

●

Autoreload capability

●

Maskable system interrupt generation when the counter reaches 0.

●

Programmable clock source (HCLK or HCLK/8)

3.15

Real-time clock (RTC) and backup registers

The RTC and the 5 backup registers are supplied through a switch that takes power either

on VDD supply when present or through the VBAT pin. The backup registers are five 32-bit

registers used to store 20 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

mode.

The RTC is an independent BCD timer/counter. Its main features are the following:

●

Calendar with subsecond, seconds, minutes, hours (12 or 24 format), week day, date,

month, year, in BCD (binary-coded decimal) format.

●

Automatically correction for 28, 29 (leap year), 30, and 31 day of the month.

●

Programmable alarm with wake up from Stop and Standby mode capability.

●

On-the-fly correction from 1 to 32767 RTC clock pulses. This can be used to

synchronize it with a master clock.

●

Digital calibration circuit with 1 ppm resolution, to compensate for quartz crystal

inaccuracy.

●

2 anti-tamper detection pins with programmable filter. The MCU can be woken up from

Stop and Standby modes on tamper event detection.

●

Timestamp feature which can be used to save the calendar content. This function can

triggered by an event on the timestamp pin, or by a tamper event. The MCU can be

woken up from Stop and Standby modes on timestamp event detection.

The RTC clock sources can be:

●

A 32.768 kHz external crystal

●

A resonator or oscillator

●

The internal low-power RC oscillator (typical frequency of 40 kHz)

●

The high-speed external clock divided by 32.

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