System window watchdog (WWDG)
RM0365
709/1080
DocID025202 Rev 7
The EWI interrupt is cleared by writing '0' to the EWIF bit in the WWDG_SR register.
Note:
When the EWI interrupt cannot be served, e.g. due to a system lock in a higher priority task,
the WWDG reset will eventually be generated.
25.3.4
How to program the watchdog timeout
You can use the formula in
to calculate the WWDG timeout.
Warning:
When writing to the WWDG_CR register, always write 1 in the
T6 bit to avoid generating an immediate reset.
Figure 281. Window watchdog timing diagram
The formula to calculate the timeout value is given by:
where:
t
WWDG
: WWDG timeout
t
PCLK
: APB1 clock period measured in ms
4096: value corresponding to internal divider
As an example, lets assume APB1 frequency is equal to 48 MHz, WDGTB[1:0] is set to 3
and T[5:0] is set to 63:
AIC
7;=
4;=#.4DOWNCOUNTER
2EFRESHNOTALLOWED
X&
2EFRESHALLOWED
4IME
4BIT
2%3%4
t
WWDG
t
PCLK1
4096
×
2
WDGTB[1:0]
×
T 5:0
[
]
1
+
(
)
×
=
ms
(
)
tWWDG 1 48000
⁄
4096
×
2
3
×
63 1
+
(
)
×
43.69 ms
=
=