RM0312 datasheet(95/275 Pages) STMICROELECTRONICS

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RM0312

Window watchdog (WWDG)

Figure 17. Window watchdog timing diagram

14.5

WWDG low power modes

Table 26. Window watchdog timing example

T[6:0]

fMASTER (MHz)

216

40h

6.144

0.768

7Fh

393.216

49.152

T6 bit

Reset

WWDG_WR

T[6:0] CNT downcounter

time

Refresh Window

Refresh not allowed

(step = 12288/fMASTER)

0x3F

Table 27. Effect of low power modes on WWDG

Mode

Description

Wait

No effect on watchdog: The downcounter continues to decrement.

Halt

WWDG_HALT in option byte

No watchdog reset is generated. The MCU enters Halt mode. The watchdog counter is

decremented once and then stops counting and is no longer able to generate a watchdog reset

until the MCU receives an external interrupt or a reset.

If an interrupt is received (refer to interrupt table mapping to see interrupts which can occur in

Halt mode), the watchdog restarts counting after the stabilization delay. If a reset is generated,

the watchdog is disabled (reset state) unless hardware watchdog is selected by option byte. For

application recommendations see Section 14.7 below.

A reset is generated instead of entering Halt mode.

Active-

halt

No reset is generated. The MCU enters Active-halt mode. The watchdog counter is not

decremented. It stops counting. When the MCU receives an oscillator interrupt or external

interrupt, the watchdog restarts counting immediately. When the MCU receives a reset the

watchdog restarts counting after the stabilization delay.

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