Iwdg Registers; Key Register (Iwdg_Kr); Prescaler Register (Iwdg_Pr) - ST STM32F205 series Reference Manual

Independent watchdog (IWDG)
17.4

IWDG registers

Refer to
The peripheral registers have to be accessed by half-words (16 bits) or words (32 bits).
17.4.1

Key register (IWDG_KR)

Address offset: 0x00
Reset value: 0x0000 0000 (reset by Standby mode)
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
Bits 31:16 Reserved, must be kept at reset value.
Bits 15:0 KEY[15:0]: Key value (write only, read 0000h)
17.4.2

Prescaler register (IWDG_PR)

Address offset: 0x04
Reset value: 0x0000 0000
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
Bits 31:3 Reserved, must be kept at reset value.
Bits 2:0 PR[2:0]: Prescaler divider
Note: Reading this register returns the prescaler value from the VDD voltage domain. This
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Section 2.2 on page 45
Reserved
These bits must be written by software at regular intervals with the key value AAAAh,
otherwise the watchdog generates a reset when the counter reaches 0.
Writing the key value 5555h to enable access to the IWDG_PR and IWDG_RLR registers
(see Section 17.3.2)
Writing the key value CCCCh starts the watchdog (except if the hardware watchdog option is
selected)
These bits are write access protected
select the prescaler divider feeding the counter clock. PVU bit of IWDG_SR must be reset in
order to be able to change the prescaler divider.
000: divider /4
001: divider /8
010: divider /16
011: divider /32
100: divider /64
101: divider /128
110: divider /256
111: divider /256
value may not be up to date/valid if a write operation to this register is ongoing. For this
reason the value read from this register is valid only when the PVU bit in the IWDG_SR
register is reset.
for a list of abbreviations used in register descriptions.
w w w w
Reserved
seeSection
RM0033 Rev 8
9 8 7 6 5
KEY[15:0]
w w w w w w w
9 8 7 6 5
17.3.2. They are written by software to
RM0033
4 3 2 1 0
w w w w w
4 3 2 1 0
PR[2:0]
rw rw rw