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-MΩ) 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.

The PCM2903C has an internal power-on reset circuit, which triggers automatically when V_DD (pin 27) exceeds 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.

9.3.5 Channel Status Information

The channel status information is fixed as consumer application, PCM mode, copyright, and digital/digital converter. All other bits are fixed as 0's except for the sample frequency, which is set automatically according to the data received through the USB.

9.3.6 Copyright Management

Isochronous-in data are affected by the serial copy management system (SCMS). When the control bit indicates that the received digital audio data are original, the input digital audio data are transferred to the host. If the data are indicated as first generation or higher, the transferred data are routed to the analog input.

Digital audio data output is always encoded as original with SCMS control.

9.5.1 USB Interface

Control data and audio data are transferred to the PCM2903C via D+ (pin 1) and D– (pin 2). All data to and from the PCM2903C are transferred at full speed. The device descriprtor contains the information described in Table 1.

The configuration descriptor contains the information described in Table 2.

The string descriptor contains the information described in Table 3.

9.5.2 Device Configuration

Figure 35 illustrates the USB audio function topology. The PCM2903C has four interfaces. Each interface consists of alternative settings.

Figure 35. USB Audio Function Topology

9.5.3 Interface Sequence

9.5.3.1 Power On, Attach, and Playback Sequence

The PCM2903C is ready for setup when the reset sequence has finished and the USB bus is attached. In order to perform certain reset sequences defined in the USB specification, V_DD, V_CCC, V_CCP1, V_CCP2, and V_CCX must rise up within 10 ms / 3.3 V. After connection has been established by setup, the PCM2903C is ready to accept USB audio data. While waiting, the audio data (idle state) and analog output are set to bipolar zero (BPZ).

When receiving the audio data, the PCM2903C stores the first audio packet, which contained 1-ms audio data, into the internal storage buffer. The PCM2903C starts playing the audio data when detecting the next start of frame (SOF) packet, as illustrated in Figure 36 and Figure 37.

Figure 36. Attach After Poweron

Figure 37. Poweron Under Attach

9.5.3.2 Play, Stop, and Detach Sequence

When the host finishes or aborts the playback, the PCM2903C stops playing after the last audio data have played, as shown in Figure 38.

Figure 38. Play, Stop, and Detach Sequence

9.5.3.3 Record Sequence

The PCM2903C starts the audio capture into the internal memory after receiving the SET_INTERFACE command, as shown in Figure 39.

Figure 39. Record Sequence

9.5.3.4 Suspend and Resume Sequence

The PCM2903C enters the suspend state after it detects a constant idle state on the USB bus (approximately 5 ms), as shown in Figure 40. While the PCM2903C enters the suspend state, the SSPND flag (pin 28) is asserted. The PCM2903C wakes up immediately after detecting a non-idle state on the USB bus.

Figure 40. Suspend and Resume Sequence