Table 8.6 shows an example device descriptor for a mouse device. The length of the descriptor is 18 bytes (bLength=18), and the descriptor type is 0x01 (bDescriptorType=0x01). The device supports USB 1.1 (bcdUSB=0x0110). bDeviceClass, bDeviceSubClass, and bDeviceProtocol are set to zero to show that the class information is in the interface descriptor. bMaxPacketSize0 is set to 8 to show that the maximum input and output packet size for endpoint 0 is 8 bytes. The next three bytes identify the device by the vendor ID, product ID, and device version number. The next three items define indexes to strings about the manufacturer, product, and the serial number. Finally, we notice that the mouse device has just one configuration (bNumConfigurations=1).
Table 8.6: Example device descriptor
| Offset | Field | Value | Description |
|---|---|---|---|
| 0 | bLength | 18 | Size is 18 |
| 1 | bDescriptorType | 0x01 | Descriptor type |
| 2 | bcdUSB | 0x0110 | Highest USB supported = USB 1.1 |
| 4 | bDeviceClass | 0x00 | Class information in interface descriptor |
| 5 | bDeviceSubClass | 0x00 | Class information in interface descriptor |
| 6 | bDeviceProtocol | 0x00 | Class information in interface descriptor |
| 7 | bMaxPacketSize0 | 8 | Maximum packet size |
| 8 | idVendor | 0x02A | XYZ Co Ltd. |
| 10 | idProduct | 0x1001 | Mouse |
| 12 | bcdDevice | 0x0011 | Device release number |
| 14 | iManufacturer | 0x20 | Index to manufacturer string |
| 15 | iProduct | 0x21 | Index of product string |
| 16 | iSerialNumber | 0x22 | Index of serial number string |
| 17 | bNumConfigurations | 1 | Number of possible configurations |