CM108B Datasheet, PDF (15/24 Pages) C-Media Electronics – A Highly Integrated USB Audio Single Chip

CM108B
USB Audio Single Chip
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
PWRSEL
3.3V
GND
3.3V
Speaker mode:
Playback only
(100mA self-powered)
Speaker mode:
Playback only
(500mA Bus-powered)
MODE
GND
Headset mode:
Playback and recording
(100mA Bus-powered)
Headset mode:
Playback and recording
(500mA Bus-powered)
USB Audio Topology Diagram
Datasheet Revision: 1.11
Page 15 / 24
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