![](http://datasheet.mmic.net.cn/30000/MQ83C154DXXX-25-883R_datasheet_2377229/MQ83C154DXXX-25-883R_84.png)
84
6384E–ATARM–05-Feb-10
AT91SAM9G20
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.