DS4201

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102099

USB DEVICE STRUCTURE Figure 3

NOTE:

For the audio streaming interface alternate setting which selects adaptive synchronization, the

isochronous synch pipe at endpoint 2 (EP2) does not exist.

AUDIO CONTROL INTERFACE

The CONTROL interface is used by the USB host to manipulate and monitor the operation of the

DS4201. Additionally, all features, control capabilities, and characteristics of the DS4201 are

communicated to the host through USB descriptors over this interface. Host communication with the

CONTROL interface is performed over a default control pipe at Endpoint 0.

The USB Audio Device Class (ADC) specification defines audio function units and terminals to describe

and operate a USB Audio device; the Endpoint 0 default control pipe is used to control the units and

terminals. USB operation of the DS4201 Audio device is controlled through Feature Units (FU), a Mixer

Unit (MU), Input Terminals (IT), an Extension Unit (XU), and an Output Terminal (OT) as shown in

Figure 3. The Input Terminal associated with the STREAMING INTERFACE makes a logical connection

to the isochronous data pipe feeding PCM coded data to the DS4201 at Endpoint 1. The DS4201

performs D/A processing of the incoming digital PCM data at this point and thus the output from this

Input Terminal is a logical cluster of analog audio signals consisting of the left and right audio channels.

The Input Terminals associated with the Auxiliary (AUX) and Microphone (MIC) inputs are for

connection to the analog line inputs; the output from these terminals are logical clusters of the respective

analog audio input source. The three Feature Units (FU) provide Mute capability for the three analog

audio clusters. The Extension Unit (XU) provides a DS4201 specific control capability which can be used

to select between two output level ranges from the sigma–delta D/A converter. The Mixer Unit (MU)

provides control for level setting and mixing of the three analog audio clusters; the control capability

consists of gain or attenuation to the incoming analog signals prior to mixing the left and right composite

channels.

INPUT TERMINALS

The ADC Input Terminal (IT) is used to receive audio information into the audio function. It also

converts the incoming audio stream into the separate logical channels embedded. USB OUT endpoints as

well as analog audio inputs are supported. The DS4201 uses three ITs: IT:TID1 connects to Endpoint 1

carrying a USB isochronous audio stream, IT:TID2 connects to the analog AUX input, and IT:TID3

connects to the analog MIC input.