Filter
Top Products
5-6 Lucent Technologies Inc.
USS-720
Instant USB
Preliminary Data Sheet, Rev. 5
USB-to-
IEEE
1284 Bridge September 1999
13
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.
* 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 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
the end of the configuration
descriptor return string.
Length of string to return in response to a GET_STRING_DESCRIPTOR
request. This address divided by two should be included in the low byte of the
wIndex field of the GET_DESCRIPTOR standard command.
Next address—end of string
descriptor.
String descriptor as defined in
USB Specification Revision 1.0
.
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.