at91sam9g20-cu ATMEL Corporation, at91sam9g20-cu Datasheet - Page 82

• Manufacturer Part Number: at91sam9g20-cu
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

13.10.3
13.10.3.1
82
AT91SAM9G20 Preliminary
USB Device Port
Enumeration Process
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
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.
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.
Table 13-6.
The device also handles some class requests defined in the CDC class.
Table 13-7.
Unhandled requests are STALLed.
Request
GET_DESCRIPTOR
SET_ADDRESS
SET_CONFIGURATION
GET_CONFIGURATION
GET_STATUS
SET_FEATURE
CLEAR_FEATURE
Request
SET_LINE_CODING
GET_LINE_CODING
SET_CONTROL_LINE_STATE
Handled Standard Requests
Handled Class Requests
®
, from Windows 98SE to Windows XP
Definition
Returns the current device configuration value.
Sets the device address for all future device access.
Sets the device configuration.
Returns the current device configuration value.
Returns status for the specified recipient.
Used to set or enable a specific feature.
Used to clear or disable a specific feature.
Definition
Configures DTE rate, stop bits, parity and number of
character bits.
Requests current DTE rate, stop bits, parity and number of
character bits.
RS-232 signal used to tell the DCE device the DTE device
is now present.
®
. The CDC document, available at
6384B–ATARM–15-Dec-08