STA680 datasheet(31/48 Pages) STMICROELECTRONICS

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STA680

Digital I/O and memory interfaces

5.4

Audio interface (AIF)

The STA680 uses a stereo I2S interface for sending the decoded digital audio back to the

tuner, where the blending with the legacy AM/FM demodulated audio occurs.

The receivers and transmitters can be used either in master mode, running with the STA680

internal audio frequency of 44.1 kHz or in slave mode running with a frequency determined

by the external device. In slave mode, the internal Audio Sample Rate Converter (ASRC,

see Chapter 5.4.3) adapts the external data rate (from 44.1 to 48 kSps) to the internal one.

5.4.1

Output serial audio interface (SAI)

The output serial audio interface is used to send the decoded audio from the HD Radio

Decoder to an external IC (e.g. TDA7786 or TDA7707).

The output SAI is an I2S interface which provides audio samples in stereo at a 44.1 kS/s

data rate in master mode. In slave mode, other sample rates (from 44.1 to 48 kS/s) are

supported by means of the internal ASRC (see Section 5.4.3).

The output SAI interface is composed by three lines: one data line and two clock lines.

The output SAI supports a 32x or 64x bit clock with 16-bit precision audio data. The 32x

clock mode has no bit padding. The 64x clock mode adds 16-bits zero padding at the end of

the 16-bit audio data. Figure 10 shows timing diagrams for the supported modes.

An oversampled audio master-clock is also available for directly interfacing the STA680 to

an external DAC. Table 8 shows the timing values for the output SAI interface.

Table 8. AIF pin list

Pin name

Designation

Type

Drive

AUDIO_IN_AWS

Digital audio input word strobe

4mA

AUDIO_IN_ABCK

Digital audio input bit clock

4mA

AUDIO_IN_ADAT

Digital audio input serial data

AWS

Digital audio output word strobe

I/O

4mA

ABCK

Digital audio output clock

I/O

4mA

ADAT

Digital audio output serial data

4mA

DAC256X

Digital audio output oversampling clock (256 x Fs)

4mA

BLEND

Digital audio output blend output

4mA

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