The following figure, Pad Behavior, illustrates the behavior of the USB pad in device mode.
In Idle state, the pad is in low power consumption mode.
In Active state, the pad is active.
The following figure, Pad Events, illustrates the pad events leading to a PAD state change.
The Suspend Interrupt bit in the Device Interrupt Flag register (INTFLAG.SUSPEND) is set when a USB Suspend state has been detected on the USB bus. The USB pad is then automatically put in the Idle state. The detection of a non-idle state sets the Wake Up Interrupt bit in INTFLAG(INTFLAG.WAKEUP) and wakes the USB pad.
The pad goes to the Idle state if the USB module is disabled or if CTRLB.DETACH is written to one. It returns to the Active state when CTRLA.ENABLE is written to one and CTRLB.DETACH is written to zero.