Information Technology Reference
In-Depth Information
Table 3-1: The device descriptor is 18 bytes.
Byte
Field
Description
0
bLength
Descriptor size in bytes (12h)
1
bDescriptorType
The constant DEVICE (01h)
2
bcdUSB
USB specification release number (BCD). For USB 2.0,
byte 2 = 00h and byte 3 = 02h.
4
bDeviceClass
Class code. For mass storage, set to 00h (the class is speci-
fied in the interface descriptor).
5
bDeviceSubclass
Subclass code. For mass storage, set to 00h.
6
bDeviceProtocol
Protocol Code. For mass storage, set to 00h.
7
bMaxPacketSize0
Maximum packet size for endpoint zero.
8
idVendor
Vendor ID. Obtained from USB-IF.
10
idProduct
Product ID. Assigned by the product vendor.
12
bcdDevice
Device release number (BCD). Assigned by the product
vendor.
14
iManufacturer
Index of string descriptor for the manufacturer. Set to 00h if
there is no string descriptor.
15
iProduct
Index of string descriptor for the product. Set to 00h if there
is no string descriptor.
16
iSerialNumber
Index of string descriptor containing the serial number.
Must be > 00h for mass-storage devices.
17
bNumConfigurations
Number of possible configurations. Typically 01h.
idVendor. Members of the USB-IF and others who pay an administrative
fee receive the rights to use a unique Vendor ID. Every device descriptor
must have an assigned Vendor ID in this field.
idProduct. The owner of the Vendor ID assigns a Product ID to identify
the device. Each Product ID is specific to a Vendor ID, so multiple vendors
can use the same Product ID without conflict.
bcdDevice. The device's release number in BCD format. The owner of the
Vendor ID assigns this value.
iManufacturer. Index to a string descriptor that contains a string describing
the manufacturer. This value is zero if there is no manufacturer string
descriptor.
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