Window watchdog (WWDG) RM0016
126/449 Doc ID 14587 Rev 8
15 Window watchdog (WWDG)
15.1 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.
15.2 WWDG main features
● Programmable free-running downcounter
● Conditional reset
– Reset (if watchdog activated) when the downcounter value becomes less than
0x40
– Reset (if watchdog activated) if the downcounter is reloaded outside the window
(see Figure 30)
● Hardware/software watchdog activation (selectable by option byte)
● Optional reset on HALT instruction (configurable by option byte)
15.3 WWDG functional description
If the watchdog is activated (the WDGA bit is set) and when the 7-bit downcounter (T[6:0]
bits) rolls over from 0x40 to 0x3F (T6 becomes cleared), it initiates a reset cycle pulling low
the reset pin. If the software refreshes the counter while the counter is greater than the value
stored in the window register, then a reset is generated.
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