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Window watchdog (WWDG) RM0008

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17 Window watchdog (WWDG)

Low-density devices are STM32F101xx, STM32F102xx and STM32F103xx

microcontrollers where the Flash memory density ranges between 16 and 32 Kbytes.

Medium-density devices are STM32F101xx, STM32F102xx and STM32F103xx

microcontrollers where the Flash memory density ranges between 64 and 128 Kbytes.

High-density devices are STM32F101xx and STM32F103xx microcontrollers where the

Flash memory density ranges between 256 and 512 Kbytes.

This section applies to the whole STM32F10xxx family, unless otherwise specified.

17.1 Introduction

The window watchdog is used to detect the occurrence of a software fault, usually

generated by external interference or by unforeseen logical conditions, which causes the

application program to abandon its normal sequence. The Watchdog circuit generates an

MCU reset on expiry of a programmed time period, unless the program refreshes the

contents of the downcounter before the T6 bit becomes cleared. An MCU reset is also

generated if the 7-bit downcounter value (in the control register) is refreshed before the

downcounter has reached the window register value. This implies that the counter must be

refreshed in a limited window.

17.2 WWDG main features

● Programmable free-running downcounter

● Conditional reset

– Reset (if watchdog activated) when the downcounter value becomes less than 40h

– Reset (if watchdog activated) if the downcounter is reloaded outside the window

(see Figure 156)

● Early wakeup interrupt (EWI): triggered (if enabled and the watchdog activated) when

the downcounter is equal to 40h. Can be used to reload the counter and prevent

WWDG reset

17.3 WWDG functional description

If the watchdog is activated (the WDGA bit is set in the WWDG_CR register) and when the

7-bit downcounter (T[6:0] bits) rolls over from 0x40 to 0x3F (T6 becomes cleared), it initiates

a reset. If the software reloads the counter while the counter is greater than the value stored

in the window register, then a reset is generated.

ST STM32F102 series User Manual

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