AT91SAM9G20 datasheet(84/832 Pages) ATMEL

84 / 832 page

6384D–ATARM–04-May-09

AT91SAM9G20 Preliminary

13.10.3

USB Device Port

A 48 MHz USB clock is necessary to use the USB Device port. It has been programmed earlier

in the device initialization procedure with PLLB configuration.

The device uses the USB communication device class (CDC) drivers to take advantage of the

installed PC RS-232 software to talk over the USB. The CDC class is implemented in all

releases of Windows

®, from Windows 98SE to Windows XP®. The CDC document, available at

www.usb.org, describes a way to implement devices such as ISDN modems and virtual COM

ports.

The Vendor ID is Atmel’s vendor ID 0x03EB. The product ID is 0x6124. These references are

used by the host operating system to mount the correct driver. On Windows systems, the INF

files contain the correspondence between vendor ID and product ID.

Atmel provides an INF example to see the device as a new serial port and also provides another

custom driver used by the SAM-BA application: atm6124.sys. Refer to the document “USB Basic

Application”, literature number 6123, for more details.

13.10.3.1

Enumeration Process

The USB protocol is a master/slave protocol. This is the host that starts the enumeration send-

ing requests to the device through the control endpoint. The device handles standard requests

as defined in the USB Specification.

The device also handles some class requests defined in the CDC class.

Unhandled requests are STALLed.

Table 13-6.

Handled Standard Requests

Request

Definition

GET_DESCRIPTOR

Returns the current device configuration value.

SET_ADDRESS

Sets the device address for all future device access.

SET_CONFIGURATION

Sets the device configuration.

GET_CONFIGURATION

Returns the current device configuration value.

GET_STATUS

Returns status for the specified recipient.

SET_FEATURE

Used to set or enable a specific feature.

CLEAR_FEATURE

Used to clear or disable a specific feature.

Table 13-7.

Handled Class Requests

Request

Definition

SET_LINE_CODING

Configures DTE rate, stop bits, parity and number of

character bits.

GET_LINE_CODING

Requests current DTE rate, stop bits, parity and number of

character bits.

SET_CONTROL_LINE_STATE

RS-232 signal used to tell the DCE device the DTE device

is now present.

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