Atmel SAM4L Xplained Pro Starter Kit Atmel ATSAM4L-XSTK ATSAM4L-XSTK Data Sheet

42023E–SAM–07/2013

 describes the USBC host mode main states.

Figure 17-14. Host mode states

After a hardware reset, the USBC host mode is in the Reset state (see 

When the USBC is enabled (USBCON.USBE = 1) in host mode (USBCON.UIMOD = 0) it enters
Idle state. As soon as the USBSTA.VBUSRQ bit is one, USBC waits for a device connection.
Once a device is connected, the USBC enters the Ready state, which does not require the USB
clock to be activated.

In host mode the USBC will suspend the USB bus by not transmitting any Start Of Frame (SOF)
packets (the Start of Frame Generation Enable bit in the Host Global Interrupt register
UHCON.SOFE is zero). The USBC enters the Suspend state when the USB bus is suspended,
and exits when SOF generation is resumed.

A device is detected by the USBC in host mode when DP or DM are not tied low, i.e., when a
device DP or DM pull-up resistor is connected. To enable this detection, the host controller has
to be notified that the VBUS is powered, which is done when USBSTA.VBUSRQ is one.

The device disconnection is detected by the host controller when both DP and DM are pulled
down.

In host mode, the term “pipe” is used instead of “endpoint”. A host pipe corresponds to a device
endpoint, as illustrated by 

 from the USB specification.

Ready

Idle

Device

Disconnection

<any

other
state>

Device

Connection

Macro off

Clock stopped

Device

Disconnection

Suspend

SOFE = 1

SOFE = 0