USB Enumeration

Enumeration is the process whereby the Host detects the presence of a Device and takes the necessary steps to ensure that the Device endpoints are added to the list of endpoints serviced by the Host.

Device Enumeration States

device-states.svg

Device Detection

The presence of a newly installed Full Speed, High Speed, or Low Speed Device is recognized by changes in the D- or D+ signal. A low-speed device places 5 V on D-, high- and full-speed devices assert 5 V on D+. The connection signals are detected by the Hub and reported to the Host. Once a Device is detected, the Host issues a RESET command to the Device.

Default State

When a RESET control signal sequence is received, the Device will manage its load, per specification, to enumerate. If the attached Device is a High-Speed device, a “chirp” will be returned and the High-Speed detection process will be completed. Once the speed has been settled, the Host reads the Device descriptor and assigns an address.

Addressed State

After setting the address, the Host reads all remaining descriptor tables for the device. If a Host determines it can service the Device’s interface endpoints and provide sufficient power, the Host issues a command informing the Device which of its configurations to activate.

Configured State

After receiving notification from the Host regarding which configuration to activate, the Device is ready to run using the active configuration.

 Learn More

© 2024 Microchip Technology, Inc.
Notice: ARM and Cortex are the registered trademarks of ARM Limited in the EU and other countries.
Information contained on this site regarding device applications and the like is provided only for your convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Microchip devices in life support and/or safety applications is entirely at the buyer's risk, and the buyer agrees to defend, indemnify and hold harmless Microchip from any and all damages, claims, suits, or expenses resulting from such use. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual property rights.