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Audio Serial Interface

Audio Data Formats and Timing

PCM1772 , PCM1773

SLES010G – SEPTEMBER 2001 – REVISED MARCH 2007

The audio serial interface for the PCM1772 and PCM1773 devices consists of a 3-wire synchronous serial port.

It includes terminals 1 (LRCK), 2 (DATA), and 3 (BCK). BCK is the serial audio bit clock, and it clocks the serial

data present on DATA into the audio interface serial shift register. Serial data is clocked into the PCM1772 and

PCM1773 devices on the rising edge of BCK. LRCK is the serial audio left/right word clock. It latches serial data

into the serial audio interface internal registers.

Both LRCK and BCK of the PCM1772 device support the slave and master modes, which are set by FMT

(register 3). LRCK and BCK are outputs during the master mode and inputs during the slave mode.

In slave mode, BCK and LRCK are synchronous to the audio system clock, SCKI. Ideally, it is recommended

that LRCK and BCK be derived from SCKI. LRCK is operated at the sampling frequency, f

. BCK can be

operated at 32, 48, and 64 times the sampling frequency.

In master mode, BCK and LRCK are derived from the system clock, and these terminals are outputs. The BCK

and LRCK are synchronous to SCKI. LRCK is operated at the sampling frequency, f

. BCK can be operated at

64 times the sampling frequency.

The PCM1772 and PCM1773 devices operate under LRCK, synchronized with the system clock. The PCM1772

and PCM1773 devices do not need a specific phase relationship between LRCK and the system clock, but do

require the synchronization of LRCK and the system clock. If the relationship between the system clock and

LRCK changes more than ±3 BCK during one sample period, internal operation of the PCM1772 and PCM1773

devices halts within 1/f

, and the analog output is kept in last data until resynchronization between system clock

and LRCK is completed.

The PCM1772 device supports industry-standard audio data formats, including standard, I

S, and left justified.

The PCM1773 device supports the I

S and left-justified data formats. Table 2 lists the main features of the audio

data interface. Figure 22 shows the data formats. Data formats are selected using the format bits, FMT[2:0] of

control register 3 in case of the PCM1772 device, and are selected using the FMT terminal in case of the

PCM1773 device. The default data format is 24-bit, left-justified, slave mode. All formats require binary 2s

complement, MSB-first audio data. Figure 23 shows a detailed timing diagram for the serial audio interface in

slave mode. Figure 24 shows a detailed timing diagram for the serial audio interface in master mode.

Table 2. Audio Data Interface

AUDIO-DATA INTERFACE FEATURE CHARACTERISTIC

PCM1772 Standard, I

S, left-justified

Audio data interface format

PCM1773 I

S, left-justified

Audio data bit length 16-, 20-, 24-bit, selectable

Audio data format MSB first, 2s complement

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