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Technical Support
On-Line Manuals
RL-ARM User's Guide (MDK v4)
RL-RTX
RL-FlashFS
RL-TCPnet
RL-CAN
RL-USB
RL-USB for USB Device Applications
RL-USB Device Library
RL-USB Device Features
RL-USB Device Software Stack
RL-USB Device Functions
RL-USB Device Source Files
RL-USB Device Configuration
Audio Device (ADC) Options
Communication Device (CDC) - ACM Options
Human Interface Device (HID) Options
Mass Storage Device (MSC) Options
Create USB Device Applications
Create ADC Applications
Create CDC ACM Applications
Create HID Applications
Create MSC Applications
Create Composite Applications
Test USB Device Applications
Compliance Tests
Test HID Client Application
RL-USB for USB Host Applications
RL-USB Host Library
RL-USB Host Features
RL-USB Host Software Stack
RL-USB Host Functions
RL-USB Host Source Files
RL-USB Host Configuration
Host Controller Driver Selection
Host Controller Driver Configuration
Host Class Driver Selection
Create USB Host Applications
Create USB Host HID Applications
HID_Kbd Example
Create USB Host MSC Applications
Create USB Host Class Driver
RL-USB Host Constants and Structures
Error constants
Speed constants
Transaction Packet Type constants
Transaction Error Type constants
USB Request Block structure (USBH_URB)
Endpoint structure (USBH_EP)
Driver Capabilites structure (USBH_HCI_CAP)
Device Class Instance structure (USBH_DCI)
Host Controller Instance structure (USBH_HCI)
Host Controller Driver structure (USBH_HCD)
USB Concepts
USB Transfer Rates
USB Network
Basic Communication Model
USB Protocol
Control Transfer
Interrupt Transfer
Isochronous Transfer
Bulk Transfer
Descriptors
Device Configuration
Device Descriptor
Configuration Descriptor
Interface Descriptor
Endpoint Descriptor
Device Qualifier Descriptor
Example Programs
Library Reference
Appendix
Device Descriptor
The Device Descriptor is the root of the descriptor tree and contains basic device information. The unique numbers, idVendor and idProduct, identify the connected device. The Windows operating system uses these numbers to determine which device driver to load.
idVendor is the number assigned to each company producing USB-based devices. The USB Implementers’ Forum is responsible for administering the assignment of Vendor IDs.
The idProduct is another 16-bit field containing a number assigned by the manufacturer to identify a specific product.
| Offset | Field | Size | Value | Description |
|---|---|---|---|---|
| 0 | bLength | 1 | Number | Size of this descriptor in bytes. |
| 1 | bDescriptorType | 1 | Constant | Device Descriptor Type. |
| 2 | bcdUSB | 2 | BCD | USB Specification Release Number in Binary-Coded Decimal (i.e., 2.10 is 210H). This field identifies the release of the USB Specification with which the device and its descriptors are compliant. |
| 4 | bDeviceClass | 1 | Class | Class code (assigned by the USB-IF). If this field is reset to zero, each interface within a configuration specifies its own class information and the various interfaces operate independently. If this field is set to a value between 1 and FEH, the device supports different class specifications on different interfaces and the interfaces may not operate independently. This value identifies the class definition used for the aggregate interfaces. If this field is set to FFH, the device class is vendor-specific. |
| 5 | bDeviceSubClass | 1 | SubClass | Subclass code (assigned by the USB-IF). These codes are qualified by the value of the bDeviceClass field. If the bDeviceClass field is reset to zero, this field must also be reset to zero. If the bDeviceClass field is not set to FFH, all values are reserved for assignment by the USB-IF. |
| 6 | bDeviceProtocol | 1 | Protocol | Protocol code (assigned by the USB-IF). These codes are
qualified by the value of the bDeviceClass and the
bDeviceSubClass fields. If a device supports class-specific
protocols on a device basis as opposed to an interface basis,
this code identifies the protocols that the device uses as
defined by the specification of the device class. If this field is reset to zero, the device does not use class specific protocols on a device basis. However, it may use class specific protocols on an interface basis. If this field is set to FFH, the device uses a vendor-specific protocol on a device basis. |
| 7 | bMaxPacketSize0 | 1 | Number | Maximum packet size for Endpoint zero (only 8, 16, 32, or 64 are valid). |
| 8 | idVendor | 2 | ID | Vendor ID (assigned by the USB-IF). |
| 10 | idProduct | 2 | ID | Product ID (assigned by the manufacturer). |
| 12 | bcdDevice | 2 | BCD | Device release number in binary-coded decimal. |
| 14 | iManufacturer | 1 | Index | Index of string descriptor describing manufacturer. |
| 15 | iProduct | 1 | Index | Index of string descriptor describing product. |
| 16 | iSerialNumber | 1 | Index | Index of string descriptor describing the device's serial number. |
| 17 | bNumConfigurations | 1 | Number | Number of possible configurations. |
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