2.12.1 AVR® Dx Additional Features

The AVR Dx devices have the option to configure the watchdog functionality using Watchdog Config (WDTCFG) fuses. This option ensures the WDT can be configured to run immediately after Reset without software support but not eliminate the need for the Watchdog Reset (WDR) instruction. The software must periodically run the WDR instruction to avoid a system reset triggered by the WDT.

Note: The configuration of the WDT cannot be modified by software if it is enabled from fuses (the LOCK bit in the WDT.STATUS register is set automatically). Refer to the AVR Dx devices data sheet for details.

In addition to the normal operation, the AVR Dx watchdog has a Window mode. The Window mode defines a time slot or window inside the time-out period during which the WDT must be reset. If the WDT is reset outside this window, either too early or too late, a system Reset will be issued. Compared to the normal operation, the Window mode can catch situations where a code error causes constant WDR execution.