Datasheet
STM32F051x Functional overview
Doc ID 018746 Rev 2 17/22
3.12.4 Independent window watchdog (IWWDG)
The independent window watchdog is based on an 8-bit prescaler and 12-bit downcounter
with user-defined refresh window. It is clocked from an independent 40 kHz internal RC and
as it 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.
3.12.5 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.
3.12.6 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)
3.13 Inter-integrated circuit interfaces (I
2
C)
Up to two I
2
C interfaces (I2C1 and I2C2) can operate in multimaster or slave modes. Both
can support Standard mode (up to 100 kbit/s) or Fast mode (up to 400 kbit/s) and I2C1
supports also Fast Mode Plus (up to 1 Mbit/s) with 20 mA output drive.
Both support 7-bit and 10-bit addressing modes, multiple 7-bit slave addresses (2
addresses, 1 with configurable mask). They also include programmable analog and digital
noise filters.
Table 4. Comparison of I2C analog and digital filters
Analog filter Digital filter
Pulse width of
suppressed spikes
≥ 50 ns
Programmable length from 1 to 15
I2C peripheral clocks
Benefits Available in Stop mode
1. Extra filtering capability vs.
standard requirements.
2. Stable length
Drawbacks
Variations depending on
temperature, voltage, process
Disabled when Wakeup from Stop
mode is enabled