AN249 Silicon_Laboratories, AN249 Datasheet - Page 14

• Manufacturer Part Number: AN249
• Description: Human Interface Device Tutorial
• Manufacturer: Silicon_Laboratories

AN249
5.4.3. Interface Descriptor
The firmware template defines the Interface Descriptor as follows:
{
},
This item describes the size of the interface descriptor and is common to all devices’ Interface Descriptors.
0x04 is the constant one byte designator for Interface descriptors.
This item distinguishes between interfaces of a configuration. Composite devices, such as a keyboard with an
embedded mouse, have more than one active interface. Each interface must be distinguished using this
designation item. The firmware template only defines a single interface, so the Interface number can be set to
0x00.
This item is useful for devices that define multiple interfaces. This firmware template assumes that only one
primary interface will be defined for the device, and sets this item to 0x00, which tells the host that the device
defines no alternate setting.
This item tells the host how many endpoints, not counting the control endpoint, will be active in this configuration.
Remember that the HID specification requires at least one IN Interrupt Endpoint be defined in every device.
This item is used to define the device’s subclass. A value of 0x03 designates this device’s class as HID.
This item further describes the device by defining which subclass of the above-defined class the device falls under.
For many HID devices, this item will be set to set to 0x00. See the HID Specification for a list of defined HID
subclasses.
This item can be used to define protocol settings for a USB device. For many HID devices, this item will be set to
set to 0x00. See the HID Specification for a list of defined HID protocols.
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0x09,
0x04,
0x00,
0x00,
0x01,
0x03,
0x00,
0x00,
0x00
0x09,
0x04,
0x00,
0x00,
0x01,
0x03,
0x00,
0x00,
0x00
// bLength
// bDescriptorType
// bInterfaceNumber
// bAlternateSetting
// bNumEndpoints
// bInterfaceClass (3 = HID)
// bInterfaceSubClass
// bInterfaceProcotol
// iInterface
// bLength
// bDescriptorType
// bInterfaceNumber
// bAlternateSetting
// bNumEndpoints
// bInterfaceClass
// bInterfaceSubClass
// bInterfaceProcotol
// iInterface
Rev. 0.2