STM32F051K4U6 Datasheet, PDF (22/104 Pages) STMicroelectronics – Low- and medium-density advanced ARM™-based 32-bit MCU with 16 to 64 Kbytes Flash, timers, ADC, DAC and comm. interfaces

Functional overview
STM32F051x
3.14.5
3.14.6
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.
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.
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 V_DD supply when present or through the V_BAT pin. The backup registers are five 32-bit
registers used to store 20 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
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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Doc ID 022265 Rev 3