【USB描述符系列】一个FTDI芯片的USB转串口

【USB描述符系列】一个FTDI芯片的USB转串口简介看了下手头的一个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-p

dadalaohua

1504人浏览 · 2021-04-11 10:59:54

dadalaohua · 2021-04-11 10:59:54 发布

【USB描述符系列】一个FTDI芯片的USB转串口

简介

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。

Device Descriptor

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

Configuration Descriptor

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

Interface Descriptor 0/0 Vendor-Specific, 2 Endpoints

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

Endpoint Descriptor 81 1 In, Bulk, 64 bytes

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

Endpoint Descriptor 02 2 Out, Bulk, 64 bytes

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