Lucent Technologies USS-720 manual USB-to- Ieee 1284 Bridge September, Onboard Device Descriptor

USS-720Instant USB	Preliminary Data Sheet, Rev. 5
USB-to-IEEE1284 Bridge	September 1999

USB Port (continued)

The format for the externally supplied data is as shown in Table 2. The addressing for the specified EEPROM device is word aligned, so the following restrictions are placed upon the starting locations for the configuration and string descriptors.

■The configuration descriptor must start at word address 0x13 (byte address 0x26).

■String descriptors must start at an address that is aligned on a double-word boundary.

Table 2. Externally Supplied Data Format

Byte Address	Word Address	Value
0x00	0x00	0x12
0x01—0x12	—	Device descriptor as defined in USB Specification Revision 1.0.
0x26	0x13	Total length of string to be returned in response to a
		GET_CONFIGURATION_DESCRIPTOR request.
0x27—0x2F	—	Configuration descriptor as defined in USB Specification Revision 1.0.
0x30—???*	—	Interface and endpoint descriptors to be returned in response to a
		GET_CONFIGURATION_DESCRIPTOR request.
Any even word	address beyond	Length of string to return in response to a GET_STRING_DESCRIPTOR
the end of the configuration		request. This address divided by two should be included in the low byte of the
descriptor return string.		wIndex field of the GET_DESCRIPTOR standard command.
Next address—end of string		String descriptor as defined in USB Specification Revision 1.0.
descriptor.

*The question marks (???) indicate that this byte address value is determined for the user’s application based on the above information. The number is going to vary depending on how the user formats their configuration information.

Note: Tables 3—14 describe the descriptor data contained in the USS-720’s internal ROM. This information can be used as a guide in creating the externally supplied descriptor data.

Onboard Device Descriptor

There is only one device descriptor for each USB device. This descriptor contains the definitions of the device class and the device subclass, among other things.

Table 3. Device Descriptor

Offset	Field	Size	Value	Description
0	bLength	Byte	0x12	Size of this descriptor in bytes.
1	bDescriptorType	Byte	0x01	Device descriptor type.
2	bcdUSB	Word	0x0100	USB Specification release number in BCD.
4	bDeviceClass	Byte	0x00	Interface specific. See Tables 6, 8, and 11.
5	bDeviceSubClass	Byte	0x00	Interface specific. See Tables 6, 8, and 11.
6	bDeviceProtocol	Byte	0x00	Interface specific. See Tables 6, 8, and 11.
7	wMaxPacketSize0	Byte	0x08	Maximum packet size for endpoint 0.
8	idVendor	Word	0x047E	Vendor ID for Lucent Technologies.
10	idProduct	Word	0x1001	Product ID.
12	bcdDevice	Word	0x0103	Device release number in BCD.
14	iManufacturer	Byte	0x00	Index of string descriptor describing manufacturer.
15	iProduct	Byte	0x00	Index of string descriptor describing this product.
16	iSerialNumber	Byte	0x00	Index of string descriptor describing the device’s serial number.
17	bNumConfigurations	Byte	0x01	Number of possible configurations.

5-6 Lucent Technologies Inc.