SAM7S256_14 Datasheet, PDF (515/775 Pages) ATMEL Corporation – ARM-based Flash MCU

35.5.3 Controlling Device States
A USB device has several possible states. Refer to Chapter 9 of the Universal Serial Bus Specification, Rev 2.0.
Figure 35-14. USB Device State Diagram
Attached
Hub Reset
or
Deconfigured
Hub
Configured
Power
Interruption
Powered
Bus Inactive
Bus Activity
Reset
Reset
Bus Inactive
Default
Bus Activity
Address
Assigned
Bus Inactive
Address
Bus Activity
Device
Deconfigured
Device
Configured
Bus Inactive
Configured
Bus Activity
Suspended
Suspended
Suspended
Suspended
Movement from one state to another depends on the USB bus state or on standard requests sent through control
transactions via the default endpoint (endpoint 0).
After a period of bus inactivity, the USB device enters Suspend Mode. Accepting Suspend/Resume requests from
the USB host is mandatory. Constraints in Suspend Mode are very strict for bus-powered applications; devices
may not consume more than 500 µA on the USB bus.
While in Suspend Mode, the host may wake up a device by sending a resume signal (bus activity) or a USB device
may send a wake up request to the host, e.g., waking up a PC by moving a USB mouse.
The wake up feature is not mandatory for all devices and must be negotiated with the host.
35.5.3.1 Not Powered State
Self powered devices can detect 5V VBUS using a PIO as described in the typical connection section. When the
device is not connected to a host, device power consumption can be reduced by disabling MCK for the UDP, dis-
abling UDPCK and disabling the transceiver. DDP and DDM lines are pulled down by 330 KΩ resistors.
SAM7S Series [DATASHEET]
6175M–ATARM–26-Oct-12
515