Maximum transmission size in bytes for endpoint 0.
Must be 8, 16, 32 or 64.
| | 8 | idVendor | 2 | Vendor id, assigned by the USB-IF. | | 10 | idProduct | 2 | Product id, assigned by the USB-IF. | | 12 | bcdDevice | 2 | Device release number. | | 14 | iManufacturer | 1 |Index for the string descriptor that describes
the manufacturer.
| | 15 | iProduct | 1 |Index for the string descriptor that describes
the product.
| | 16 | iSerialNumber | 1 |Index for the string descriptor that describes
the serial number.
| | 17 | bNumConfigurations | 1 | Device configurations used by the device. | * The different device configurations are mapped using **configuration descriptors**. B. describe the current consumption or the number of interfaces of a device configuration. The host can only activate one device configuration at a time. | Offset | Field | Size | Description | | ------ | ------------------- | ---- | -------------------------------------------------------------------------------- | | 0 | bLength | 1 | Descriptor size in bytes. | | 1 | bDescriptorType | 1 | CONFIGURATION descriptor (=2). | | 2 | wTotalLength | 2 | Size of the complete configuration in bytes. | | 4 | bNumInterfaces | 1 | Number of interfaces. | | 5 | bConfigurationValue | 1 | Configuration index for this configuration descriptor. | | 6 | iConfiguration | 1 |Index for the string descriptor that describes
this configuration.
| | 7 | bmAttributes | 1 | Interface attributes. | | 8 | bMaxPower | 1 | Power consumption of the device (2 mA / bit). | * Each interface is described by an **interface descriptor** and, unlike the device configurations, several interfaces can be active at the same time. An interface descriptor describes i. e. the number of endpoints and the class of a device. | Offset | Field | Size | Description | | ------ | ------------------ | ---- | ------------------------------------------------------------------------------ | | 0 | bLength | 1 | Descriptor size in bytes. | | 1 | bDescriptorType | 1 | INTERFACE descriptor (=4). | | 2 | bInterfaceNumber | 1 | Interface id. | | 3 | bAlternateSetting | 1 | Additional settings for this interface. | | 4 | bNumEndpoints | 1 |Number of endpoints used by this interface
(without endpoint 0).
| | 5 | bInterfaceClass | 1 | Interface class code, assigned by the USB-IF. | | 6 | bInterfaceSubClass | 1 | Interface sub class code, assigned by the USB-IF. | | 7 | bInterfaceProtocol | 1 | Interface protocol code, assigned by the USB-IF. | | 8 | iInterface | 1 |Index for the string descriptor that describes
this interface.
| * The individual endpoints of each interface are described by **endpoint descriptors**. These include e.g. information such as the size of the end point and whether it is an *IN* or *OUT* endpoint. | Offset | Field | Size | Description | | ------ | ---------------- | ---- | ------------------------------------------------------------------------------------------------- | | 0 | bLength | 1 | Descriptor size in bytes. | | 1 | bDescriptorType | 1 | INTERFACE descriptor (=5). | | 2 | bEndpointAddress | 1 | Endpoint address. | | 3 | bmAttributes | 1 | Endpoint attributes. | | 4 | wMaxPacketSize | 2 | Endpoint message size | | 6 | bInterval | 1 | Polling interval. 1 ms / bit for low and high speed devices, 125 µs / bit for high speed devices. | * Optional **string descriptors** * Manufacturer String * Product String * Serial Number String **String descriptor 0** | Offset | Field | Size | Description | | ---------- | --------------- | ---- | -------------------------- | | 0 | bLength | 1 | Descriptor size in bytes. | | 1 | bDescriptorType | 1 | INTERFACE descriptor (=3). | | 2 | wLANGID\[0] | 2 | LANGID code 0 | | ... | ... | ... | ... | | 2 + x \* 2 | wLANGID\[x] | 2 | LANGID code x | **Common string descriptor** | Offset | Field | Size | Description | | ------ | --------------- | ---- | -------------------------- | | 0 | bLength | 1 | Descriptor size in bytes. | | 1 | bDescriptorType | 1 | INTERFACE descriptor (=3). | | 2 | bString | 2 | Unicode string | A communication between host and device require the help of endpoints and pipelines. Each endpoint is defined as a sink or source of data and is connected to the host via a pipeline. In total, each USB device can have up to 16 *IN* and 16 *OUT* endpoints, whereby the size is variable and usually depends on the USB controller used. A special end point is **endpoint 0**, because this end point is used both as an IN and an OUT end point. This end point is also the standard end point that is used when configuring the device. A data transfer at is called a **USB transaction**. The USB standard knows three different types of transactions: | Transaction | Description | | ----------- | ------------------------------------------------------------------------------ | | *IN* | Data transmission from device to host. | | *OUT* | Data transmission from host to device. | | *SETUP* |OUT transmission to send/request
configuration and control data.
| Such a transaction can be carried out with one of four different types of transfer, each type of transfer offering its own particular advantages. | Transmission | Package size in bytes | Description | | ------------ | ----------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------- | | Bulk |Low speed: Not defined
Full speed: 8, 16, 32, 64
High speed: Up to 512
|Use this mode to transmit many data
without error. No guaranteed bandwidth.
| | Interrupt |Low speed: 1 to 8
Full speed: 1 to 64
High speed: Up to 1024
|Use this to send new data from inputs in
a device to host communication
| | Isochronous |Low speed: Not allowed
Full speed: Up to 1023
High speed: Up to 1024
|Guaranteed bandwidth but without
error detection.
| | Control |Low speed: 8
Full speed: 8, 16, 32, 64
High speed: 64
|Bidirectional transmission for device
configuration. Only used for endpoint 0.
| To communicate with the host, each USB device must be able to understand and operate a certain number of commands, the so-called **standard requests**. The host uses these requests to request as much information as possible about the new device. After the host has collected all the necessary information, the requests are used for the configuration and initialization of the inserted USB device. | **bmRequestType** | **bReqest** | **wValue** | **wIndex** | **wLength** | **Data** | | --------------------------------- | -------------------------------- | ----------------------------------------------- | ------------------------------------------ | --------------- | ----------------------------------------------------------------- | |0x00
0x01
0x02
|CLEAR\_FEATURE
(1)
Null
Interface
Endpoint
| 0 | - | | 0x80 |GET\_CONFIGURATION
(8)
GET\_DESCRIPTOR
(6)
Descriptor type (H)
and index (L)
| Null or language id | Descriptor size | Descriptor | | 0x81 |GET\_INTERFACE
(10)
0x80
0x81
0x82
|GET\_STATUS
(0)
0
Interface
Endpoint
| 2 |Device status
Interface status
Endpoint status
| | 0x00 |SET\_ADDRESS
(5)
SET\_CONFIGURATION
(9)
SET\_DESCRIPTOR
(7)
Descriptor type (H)
and index (L)
| Null oder language id | Descriptor size | Descriptor | |0x00
0x01
0x02
|SET\_FEATURE
(3)
0
Interface
Endpunkt
| 0 | - | | 0x01 |SET\_INTERFACE
(11)
SYNCH\_FRAME
(12)