30.3.3 Operation

Before the SWDT is enabled, its counter (CNT) is zero, and all bits in the Interrupt Flags (INTFLAGS) register are zero. Once the SWDT is enabled by writing a ‘1’ to the ENABLE bit in the CTRLA register, the value in the RESET register is loaded into the counter (CNT) and begins decrementing in accordance with the MODE bit selection.

The counter (CNT) register may be read at any time, but any attempt to write to the CNT register will have no effect. The software can reload the RESET value into the CNT register before it reaches zero and generates an expiration (EXP) event, but it must do so using a specific two-step, timed sequence. This two-step sequence requires the software to issue a PRECLEAR command followed by a CLEAR command using the COMMAND register, as described in further detail below.