1.6.1 Fused Enabling of the Watchdog

The WDT can be initialized automatically during system Reset by writing the fuses corresponding to the Normal mode and to Window mode. These fuses will determine both the watchdog timer timeout period and the duration of the WDT closed window, and can be used to enable the WDT at start-up. Refer to the data sheet for more information about the fuses controlling the WDT.

Note: The Window mode cannot be enabled through fuses as it is an advantage to be able to enable it run-time to ensure proper timing when using Window mode.

To provide maximum protection, it is possible to program the Watchdog Lock (WDLOCK) fuse, which ensures that the WDT cannot be disabled during run-time – neither accidentally, nor on purpose. This can be desirable if considering that a system failure may for some reason impair the enabling of the watchdog at run-time (in the firmware).

Figure 1-4. State Chart for Enabling WD through Fuses