Datasheet

DocID024030 Rev 10 37/239
STM32F427xx STM32F429xx Functional overview
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3.22.4 Independent watchdog
The independent watchdog is based on a 12-bit downcounter and 8-bit prescaler. It is
clocked from an independent 32 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.
3.22.5 Window watchdog
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.
3.22.6 SysTick timer
This timer is dedicated to real-time operating systems, but could also be used as a standard
downcounter. It features:
• A 24-bit downcounter
• Autoreload capability
• Maskable system interrupt generation when the counter reaches 0
• Programmable clock source.
3.23 Inter-integrated circuit interface ( I
2
C)
Up to three I²C bus interfaces can operate in multimaster and slave modes. They can
support the standard (up to 100 KHz), and fast (up to 400 KHz) modes. They support the
7/10-bit addressing mode and the 7-bit dual addressing mode (as slave). A hardware CRC
generation/verification is embedded.
They can be served by DMA and they support SMBus 2.0/PMBus.
The devices also include programmable analog and digital noise filters (see Table 7).
3.24 Universal synchronous/asynchronous receiver transmitters
(USART)
The devices embed four universal synchronous/asynchronous receiver transmitters
(USART1, USART2, USART3 and USART6) and four universal asynchronous receiver
transmitters (UART4, UART5, UART7, and UART8).
These six interfaces provide asynchronous communication, IrDA SIR ENDEC support,
multiprocessor communication mode, single-wire half-duplex communication mode and
have LIN Master/Slave capability. The USART1 and USART6 interfaces are able to
Table 7. 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
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