When a pin reset is canceled while the input of the NMI pin is low, the DNMIF flag is set to 1 (a cancel request by the NMI pin is generated).
During a reset, NMI pin input is disabled, so the internal signal is fixed high. After cancellation of a reset, NMI is input-only, so the pin state is conveyed internally.
For this reason, if reset is canceled when NMI input is low, the internal signal changes from high to low, setting the DNMIF flag to 1.
If reset is canceled when NMI input is high, the internal signal does not change, so the DNMIF flag remains 0 (no cancel request by the NMI pin is generated).