STM32F302xx/STM32F303xx
Functional overview
3.16.5
Window watchdog (WWDG)
The 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
main clock. It has an early warning interrupt capability and the counter can be frozen in
debug mode.
3.16.6
SysTick timer
This timer is dedicated to real-time operating systems, but could also be used as a standard
down counter. It features:
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A 24-bit down counter
Autoreload capability
Maskable system interrupt generation when the counter reaches 0.
Programmable clock source
3.17
Real-time clock (RTC) and backup registers
The RTC and the 16 backup registers are supplied through a switch that takes power from
either the V supply when present or the V
pin. The backup registers are sixteen 32-bit
DD
BAT
registers used to store 64 bytes of user application data when V power is not present.
DD
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. It supports the following features:
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Calendar with subsecond, seconds, minutes, hours (12 or 24 format), week day, date,
month, year, in BCD (binary-coded decimal) format.
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Automatic correction for 28, 29 (leap year), 30 and 31 days of the month.
Two programmable alarms 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.
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Digital calibration circuit with 1 ppm resolution, to compensate for quartz crystal
inaccuracy.
Three anti-tamper detection pins with programmable filter. The MCU can be woken up
from Stopand Standby modes on tamper event detection.
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. The MCU can be
woken up from Stop and Standby modes on timestamp event detection.
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17-bit Auto-reload counter for periodic interrupt with wakeup from STOP/STANDBY
capability.
The RTC clock sources can be:
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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.
Doc ID 023353 Rev 5
25/133
STMICROELECTRONICS [ ST ]
