UPSD3422 datasheet(148/293 Pages) STMICROELECTRONICS

148 / 293 page

USB interface

uPSD34xx

148/293

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Control Transfers (see Figure 53)

Control transfers are used to configure and send commands to a device. Control

transfers consist of two or three stages:

–SETUP

This stage always consists of a data packet with eight bytes of USB CONTROL

data.

–

DATA stage (optional)

If the CONTROL data is such that the host is requesting information from the

device, the SETUP stage is followed by a DATA stage. In this case, the host sends

an IN token and the device responds with the requested data in the data packet.

–

STATUS stage

This stage is essentially a handshake informing the device of a successfully

completed control operation.

25.2.1

Enumeration

Enumeration is the process that takes place when a device is first connected to the USB.

During enumeration, the host requests information from the device about what it is, how

many endpoints it has, the power requirements, bus bandwidth requirements, and what

driver to load.

Once the enumeration process is complete, the device is available for use.

The enumeration process consists of a series of six steps as follows:

When a device is first connected to the USB, its address is zero. Upon detecting a new

device connected to the USB, the host sends a Get_Descriptor request to address

zero, endpoint0.

The device, upon receiving a Get_Descriptor request, sends data back to the host

identifying what it is.

The host resets the device and then sends a Set_Address request. This is a unique

address that identifies it from all other devices connected to the USB. This address

remains in effect until the device is disconnected from the USB.

The host sends more Get_Descriptor requests to the device to gather more detailed

information about it and then loads the specified driver.

The host will setup and enable the endpoints defined by the device.

The device is now configured and ready for use with the host communicating to the

device using the assigned address and endpoints.

UPSD3422 Datasheet(PDF) 148 Page - STMicroelectronics