CM108B Datasheet, PDF (11/24 Pages) C-Media Electronics – A Highly Integrated USB Audio Single Chip

CM108B
USB Audio Single Chip
7 Function description
7.1 USB interface
The CM108B integrates USB transceiver, PLL and regulator modules, meaning only a few passive components are
necessary for USB interface connection. Default USB descriptors are embedded in the CM108B, so no additional
design effort is needed for generic USB operation. For custom orders, customers can attach a 93C46 EEPROM to
override the embedded VID, PID, product and manufacturer strings, and initial/max/min volume settings. The
CM108B automatically detects the 93C46, and the overwrite function is performed at start up.
7.1.1 USB audio topology diagram for headset
The CM108B supports headset and speaker topology that can be selected by MODE pin. The topology setting as
following: MODE=0, Headset Topology; MODE=1, Speaker Topology
0X01
IT
0X0F
MIXER
0X09
FEA
0X06
OT
0X0D
FEA
0X02
IT
0X0A
FEA
0X08
SEL
0X07
OT
Device Descriptor
Offset
Field
Size
0
bLength
1
1
bDescriptorType
1
2
bcdUSB
2
4
bDeviceClass
1
5
bDeviceSubClass
1
6
bDeviceProtocol
1
7
bMaxPacketSize0
1
8
idVendor
2
10
idProduct
2
12
bcdDevice
2
14
iManufacturer
1
15
iProduct
1
16
iSerialNumber
1
17 bNumConfigurations 1
Value (Hex)
12
01
0110
00
00
00
8
0d8c
0012
0100
Description
Total 18 Bytes
Device Descriptor
USB 1.1 compliant.
Device class specified by interface
Device subclass specified by interface
Device protocol specified by interface
Endpoint zero Size = 8 bytes
Vendor ID
Product ID
Device compliant to the Audio Device Class specification
version 1.00
01
Index of string descriptor describing manufacturer
02
Index of string descriptor describing product
00
Index of string descriptor describing the device’s serial
number
01
Configurations number = 1
Configuration Descriptor
Datasheet Revision: 1.11
Page 11 / 24
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