Prior to device detection the software must set the VBUS is OK bit in CTRLB (CTRLB.VBUSOK) register when the VBUS is available. This notifies the USB host that USB operations can be started. When the bit CTRLB.VBUSOK is zero and even if the USB HOST is configured and enabled, host operation is halted. Setting the bit CTRLB.VBUSOK will allow host operation when the USB is configured.
The Device detection is managed by the software using the Line State field in the Host Status (STATUS.LINESTATE) register. The device connection is detected by the host controller when DP or DM is pulled high, depending of the speed of the device.
The device disconnection is detected by the host controller when both DP and DM are pulled down using the STATUS.LINESTATE registers.
The Device Connection Interrupt bit in INTFLAG (INTFLAG.DCONN) is set if a device connection is detected.
The Device Disconnection Interrupt bit in INTFLAG (INTFLAG.DDISC) is set if a device disconnection is detected.