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CM108B

USB Audio Single Chip

Datasheet Revision: 1.11 www.cmedia.com.tw

7.2 Jumper pins and mode setting:

The CM108B can be configured via several jumper pins. These jumper pin settings affect both USB descriptors and

USB audio topology.

7.2.1 Mode pin and msel pin

If the MODE pin is pushed up to 3.3V (speaker mode), a playback-only function is activated and no recording function

is declared to the host. At this setting, the MSEL pin is ignored and only one input terminal, one output terminal and

one feature unit is declared in the USB audio topology.

If the MODE pin is pulled low (headset mode), a full-duplex playback and recording function is reported to the host.

The MSEL pin setting activates one mixer unit and one feature unit.

 When MSEL = 1, the mixer is enabled (AA-path enabled), but with default mute setting

 When MSEL = 0, the mixer is disabled (AA-path disabled)

The above USB audio topology (7.1.4) is an example of headset mode with enabled mixer.

7.2.2 Mode pin and pwrsel pin

The PWRSEL pin affects the power configuration of the CM108B. Together with the MODE pin, there are a total of 4

programmable combinations.

Combinations

MODE

3.3V

GND

PWRSEL

3.3V

Speaker mode:

Playback only

(100mA self-powered)

Headset mode:

Playback and recording

(100mA Bus-powered)

GND

Speaker mode:

Playback only

(500mA Bus-powered)

Headset mode:

Playback and recording

(500mA Bus-powered)

USB Audio Topology Diagram

CM108B

USB Audio Single Chip

Datasheet Revision: 1.11 www.cmedia.com.tw

7.3 HID feature

USB protocols can configure devices at startup or when they are plugged in at run time. These devices are

categorized 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 to control the operation of computer systems. Typical

examples of HID class devices include:

The CM108B’s HID feature allows users to set volume up, volume down, playback mute and recording mute button

pins, and reports the changes to the host to synchronize host side settings. In addition, all CM108B internal registers

can be accessed via HID function call.

7.3.1 HID descriptors

HID Interface Descriptor

Offset

Field

Size

Value (Hex)

Description

0

bLength

1

09

Size of this descriptor: 9 bytes

1

bDescriptorType

1

04

Interface descriptor type

2

bInterfaceNumber

1

03

Interface number: 3

3

bAlternateSetting

1

00

Alternate: 0

4

bNumEndpoints

1

01

Number of endpoints used by this interface: 1

5

bInterfaceClass

1

03

Interface class: HID

6

bInterfaceSubClass

1

00

Subclass: no

7

bInterfaceProtocol

1

00

Must be set to 0

8

iInterface

1

00

String descriptor index that characterizes this interface

HID Descriptor

Offset

Field

Size

Value (Hex)

Description

0

bLength

1

09

Total: 9 bytes

1

bDescriptorType

1

21

HID descriptor type

2

bcdHID

2

0100

HID class version 1.0

4

bCountryCode

1

00

5

bNumDescriptors

1

01

6

bDescriptorType

1

22

Report descriptor

7

wDescriptorLength

2

003C

Total size of the optional descriptor: 60 bytes

Interrupt IN Endpoint Descriptor

Offset

Field

Size

Value (Hex)

Description

0

bLength

1

07

Total: 7 bytes

1

bDescriptorType

1

05

Endpoint descriptor type

2

bEndpointAddress

1

87

In Endpoint Number = 3

3

bmAttributes

1

03

Interrupt endpoint type

4

wMaxPacketSize

2

0004

Maximum packet size: 4 bytes

6

bInterval

1

2

2ms

CM108B

USB Audio Single Chip

Datasheet Revision: 1.11 www.cmedia.com.tw

7.4 Internal Registers

All of CM108B’s internal registers can be accessed via generic HID functional calls without the need to develop a

kernel mode driver. In total, 4 bytes of data can be read or written from the HID. The input report is for read and the

output report is for write. These internal registers of CM108B are used to control GPIO pins, S/PDIF output and

EEPROM data access.

Access via HID Class Command

HID interrupt will occur when HID_IR0-3 are updated by button status, or GPI in case HID_IR0[7:6] == 2’b00).

HID Get_Input_Report Format

Command Format:

bmRequestType

bRequest

wValue

wIndex

wLength

Data

8’h A1

8’h 01

(Get_Report)

16’h 01 00

(Rpt Type + Rpt ID)

16’h 00 02

16’h 00 03

(Interface)

16’h 00 04

(4 bytes)

Report

Input Data Format:

byte 0

HID IR0[7:0]

byte1

HID IR1[7:0]

byte2

HID IR2[7:0]

byte3

HID IR3[7:0]

HID Set_Output_Report Format

Command Format:

bmRequestType

bRequest

wValue

wIndex

wLength

Data

8’h 21

8’h 09

(Set_Report)

16’h 02 00

(Rpt Type + Rpt ID)

16’h 00 02

16’h 00 03

(Interface)

16’h 00 04

(4 bytes)

Report

Output Data Format:

byte 0

HID OR0[7:0]

byte1

HID OR1[7:0]

byte2

HID OR2[7:0]

byte3

HID OR3[7:0]

HID_IR0 (HID input report byte 0)

Offset: 0x00

Bits

Read/Write

Description

Default

7-6

R

00: HID_IR1 is used as GPI,

10: values written to HID_IR0-3 are also mapped to

EPROM_DATA0-1 and EEPROM_CTRL

Others: reserved

0x0

5-4

R

Reserved

0x0

3

R

0: no activity on record/mute button

1: record/mute button pressed then released

0x0

2

R

0: no activity on playback/mute button

1: playback/mute button pressed then released

0x0

1

R

0: volume-down button released

0x0