RM0440 Rev 4 1931/2126
RM0440 Independent watchdog (IWDG)
1937
42.3.3 Hardware watchdog
If the “Hardware watchdog” feature is enabled through the device option bits, the watchdog
is automatically enabled at power-on, and generates a reset unless the IWDG key register
(IWDG_KR) is written by the software before the counter reaches end of count or if the
downcounter is reloaded inside the window.
42.3.4 Low-power freeze
Depending on the IWDG_STOP and IWDG_STBY options configuration, the IWDG can
continue counting or not during the Stop mode and the Standby mode, respectively. If the
IWDG is kept running during Stop or Standby modes, it can wake up the device from this
mode. Refer to User and read protection option bytes for more details.
42.3.5 Register access protection
Write access to IWDG prescaler register (IWDG_PR), IWDG reload register (IWDG_RLR)
and IWDG window register (IWDG_WINR) is protected. To modify them, the user must first
write the code 0x0000 5555 in the IWDG key register (IWDG_KR). A write access to this
register with a different value breaks the sequence and register access is protected again.
This is the case of the reload operation (writing 0x0000 AAAA).
A status register is available to indicate that an update of the prescaler or of the
downcounter reload value or of the window value is ongoing.
42.3.6 Debug mode
When the device enters Debug mode (core halted), the IWDG counter either continues to
work normally or stops, depending on the configuration of the corresponding bit in
DBGMCU freeze register.
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