CM108 Datasheet, PDF (18/29 Pages) C-Media Electronics – USB Audio I/O Controller

CM108
Integration Dual DAC, Earphone Driver, ADC,
Microphone Booster, PLL, Regulator, and USB Transceiver
7.3 HID Feature
HID feature is provided by CM108 so user setting to Volume Up, Volume Down, and
Playback Mute button pin is reported to the host to synchronize host side setting. In addition,
all CM108 internal registers can be accessed via HID function call.
7.2.3 What’s HID
USB protocols can configure devices at startup or when they are plugged in at run time.
These devices are broken into various device classes. Each device class defines the
common behavior and protocols for devices that serve similar functions. The HID (Human
Interface Device) class is one of the device classes.
The HID class consists primarily of devices that are used by humans to control the operation
of computer systems. Typical examples of HID class devices include:
- Keyboards and pointing devices, for example: mouse, trackballs, and joysticks.
- Front-panel controls, for example: knobs, switches, buttons, and sliders.
- Controls that might be found on devices such as VCR remote controls, games or
simulation devices, for example: data gloves, throttles, and steering wheels.
- Devices that may not require human interaction but provide data in a similar format to
HID class devices, for example: bar-code readers, thermometers, or voltmeters.
7.2.4 HID Descriptor
HID Interface Descriptor
Offset
Field
Size
0
bLength
1
1 bDescriptorType 1
2 bInterfaceNumber 1
3 bAlternateSetting 1
4 bNumEndpoints 1
5
bInterfaceClass
1
6 bInterfaceSubClass 1
7 bInterfaceProtocol 1
8
iInterface
1
Value (Hex)
Description
09
Size of this descriptor: 9 byte
04
INTERFACE descriptor type
03
Number of Interface: 3
00
alternate 0
01
Number of endpoints used by this
Interface: 1
03
HID Interface Class
00
No Subclass
00
Must be set to 0
00
Index of a string descriptor that
describes this interface.
Date: Nov/01/2004
- 17 -
Version: 1.5