PCM2903C

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SBFS038A – JUNE 2012 – REVISED SEPTEMBER 2015

9.3 Feature Description

9.3.1 End-Points

The PCM2903C has the following four end-points:

•

Control end-point (EP number 0)

•

Isochronous-out audio data stream end-point (EP number 2)

•

Isochronous-in audio data stream end-point (EP number 4)

•

HID end-point (EP number 5)

The control end-point is a default end-point. The control end-point is used to control all functions of the

PCM2903C by the standard USB request and an USB audio class specific request from the host. The

isochronous-out audio data stream end-point is an audio sink end-point, which receives the PCM audio data. The

isochronous-out audio data stream end-point accepts the adaptive transfer mode. The isochronous-in audio data

stream end-point is an audio source end-point that transmits the PCM audio data. The isochronous-in audio data

stream end-point uses asynchronous transfer mode. The HID end-point is an interrupt-in end-point. HID end-

point reports HID0, HID1, and HID2 pin status every 32 ms.

The human interface device (HID) pins are defined as consumer control devices. The HID function is designed

as an independent end-point from both isochronous-in and -out end-points. Therefore, the result obtained from

the HID operation depends on the host software. Typically, the HID function is used as the primary audio-out

device.

9.3.2 Clock and Reset

The PCM2903C requires a 12-MHz (±500 ppm) clock for the USB and audio function, which can be generated

by a built-in crystal oscillator with a 12-MHz crystal resonator or supplied by an external clock. The 12-MHz

crystal resonator must be connected to XTI (pin 21) and XTO (pin 20) with one high (1-M

Ω) resistor and two

small capacitors, the capacitance of which depends on the load capacitance of the crystal resonator. If the

external clock is used, the clock must be supplied to XTI, and XTO must be open.

2.5 V typical (2.7 V to 2.2 V). Approximately 700

μs is required until internal reset release.

9.3.3 Digital Audio Interface

The PCM2903C employs both S/PDIF input and output. Isochronous-out data from the host are encoded to the

S/PDIF output and the DAC analog output. Input data are selected as either S/PDIF or ADC analog input. When

the device detects an S/PDIF input and successfully locks on the received data, the isochronous-in transfer data

source is automatically selected from S/PDIF itself; otherwise, the data source selected is the ADC analog input.

This feature is a customer option. It is the responsibility of the user to implement this feature.

9.3.4 Supported Input/Output Data

The following data formats are accepted by the S/PDIF input and output. All other data formats are unable to use

S/PDIF.

•

48-kHz 16-bit stereo

•

44.1-kHz 16-bit stereo

•

32-kHz 16-bit stereo

Any mismatch of the sampling rate between the input S/PDIF signal and the host command is not acceptable.

Any mismatch of the data format between the input S/PDIF signal and the host command may cause unexpected

results, with the following exceptions:

•

Recording in monaural format from stereo data input at the same data rate

•

Recording in 8-bit format from 16-bit data input at the same data rate

A combination of these two conditions is not acceptable.

For playback, all possible data-rate sources are converted to 16-bit stereo format at the same source data rate.

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