当前位置 博文首页 > dadalaohua的博客：【USB描述符系列】一个FTDI芯片的USB转串口
看了下手头的一个FTDI芯片的USB转串口模块的描述符是什么样的。从描述符可以看到，这个USB 转Serial设备是一个厂商自定义类Vendor specific，难怪这种类型模块有一大堆兼容性问题，原来都不是标准类，所以很多时候是需要额外安装厂商驱动的。在Configuration Descriptor中看到声明自己是一个自供电(Self-powered)的设备，让我感到很诧异。设备有两个bulk端点，传输数据使用bulk传输。是一个Full Speed设备。详细的看USB描述符。
下面是这个USB转串口模块的USB描述符。
| Offset | Field | Size | Value | Description |
|---|---|---|---|---|
| 0 | bLength | 1 | 12h | Size of this descriptor |
| 1 | bDescriptorType | 1 | 01h | Device |
| 2 | bcdUSB | 2 | 0110h | USB Spec 1.1 |
| 4 | bDeviceClass | 1 | 00h | Class info in Ifc Descriptors |
| 5 | bDeviceSubClass | 1 | 00h | Unused |
| 6 | bDeviceProtocol | 1 | 00h | Unused |
| 7 | bMaxPacketSize0 | 1 | 08h | 8 bytes |
| 8 | idVendor | 2 | 0403h | Vendor ID |
| 10 | idProduct | 2 | 6001h | Product ID |
| 12 | bcdDevice | 2 | 0400h | 4.00 |
| 14 | iManufacturer | 1 | 01h | Index to string descriptor that contains the string < Your Name > in Unicode |
| 15 | iProduct | 1 | 02h | Index to string descriptor that contains the string < Your Product Name > in Unicode |
| 16 | iSerialNumber | 1 | 00h | Unused |
| 17 | bNumConfigurations | 1 | 01h | One configuration |
| Offset | Field | Size | Value | Description |
|---|---|---|---|---|
| 0 | bLength | 1 | 09h | Size of this descriptor |
| 1 | bDescriptorType | 1 | 02h | Configuration |
| 2 | wTotalLength | 2 | 0020h | Length of the total configuration block, including this descriptor, in bytes |
| 4 | bNumInterfaces | 1 | 01h | One interfaces |
| 5 | bConfigurationValue | 1 | 01h | ID of this configuration |
| 6 | iConfiguration | 1 | 00h | Unused |
| 7 | bmAttributes | 1 | C0h | Self Powered |
| 4…0: Reserved | . . . 00000 | Unused | ||
| 5: Remote Wakeup | . .0 . . . . . | No | ||
| 6: Self Powered | . 1 . . . . . . | Yes | ||
| 7: Reserved (set to one) (bus-powered for 1.0) | 1 . . . . . . . | Unused | ||
| 8 | bMaxPower | 1 | 2Dh | 90 mA |
| Offset | Field | Size | Value | Description |
|---|---|---|---|---|
| 0 | bLength | 1 | 09h | Size of this descriptor |
| 1 | bDescriptorType | 1 | 04h | INTERFACE |
| 2 | bInterfaceNumber | 1 | 00h | Index of this interface |
| 3 | bAlternateSetting | 1 | 00h | Index of this setting |
| 4 | bNumEndpoints | 1 | 02h | 2 endpoints |
| 5 | bInterfaceClass | 1 | FFh | Vendor-Specific |
| 6 | bInterfaceSubClass | 1 | FFh | Vendor-Specific |
| 7 | bInterfaceProtocol | 1 | FFh | Vendor-Specific |
| 8 | iInterface | 1 | 02h | Index of string descriptor describing this interface |
| Offset | Field | Size | Value | Description |
|---|---|---|---|---|
| 0 | bLength | 1 | 07h | Size of this descriptor |
| 1 | bDescriptorType | 1 | 05h | Endpoint |
| 2 | bEndpointAddress | 1 | 81h | 1 In |
| 3 | bmAttributes | 1 | 02h | Bulk |
| 1…0: Transfer Type | . . . . . .10 | Bulk | ||
| 7…2: Reserved | 000000 . . | Unused | ||
| 4 | wMaxPacketSize | 2 | 0040h | 64 bytes |
| 6 | bInterval | 1 | 00h | Unused |
| Offset | Field | Size | Value | Description |
|---|---|---|---|---|
| 0 | bLength | 1 | 07h | Size of this descriptor |
| 1 | bDescriptorType | 1 | 05h | Endpoint |
| 2 | bEndpointAddress | 1 | 02h | 2 Out |
| 3 | bmAttributes | 1 | 02h | Bulk |
| 1…0: Transfer Type | . . . . . .10 | Bulk | ||
| 7…2: Reserved | 000000 . . | Unused | ||
| 4 | wMaxPacketSize | 2 | 0040h | 64 bytes |
| 6 | bInterval | 1 | 00h | Unused |
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