User's Manual

44
7.3 Digital Audio Interface (I2S)
The digital audio interface supports the industry standard formats for I
2
S, left-justified (LJ) or right-
justified(RJ). The interface shares the same pins as the PCM interface, which means that each audio
bus is mutually exclusive in its usage. Table 18 lists these alternative functions. Figure 22 shows the
timing diagram.
PCM Interface
I2S Interface
PCM_OUT
SD_OUT
PCM_IN
SD_IN
PCM_SYNC
WS
PCM_CLK
SCK
Table 18: Alternative Functions of the Digital Audio Bus Interface on the PCM Interface
Table 19 describes the values for the PS Key (PSKEY_DIGITAL_AUDIO_CONFIG) that is used to set-
up the digital audio interface. For example, to configure an I
2
S interface with 16-bit SD data set
PSKEY_DIGITAL_CONFIG to 0x0406.
Bit
Mask
Name
Description
D[0]
0x0001
CONFIG_JUSTIFY_FORMAT
0 for left justified, 1 for right justified
D[1]
0x0002
CONFIG_LEFT_JUSTIFY_DELAY
For left justified formats: 0 is MSB of SD data
occurs in the first SCLK period following WS
transition. 1 is MSB of SD data occurs in the
second SCLK period.
D[2]
0x0004
CONFIG_CHANNEL_POLARITY
For 0, SD data is left channel when WS is
high. For 1 SD data is right channel.
D[3]
0x0008
CONFIG_AUDIO_ATTEN_EN
For 0, 17 bit SD data is rounded down to 16
bits. For 1, the audio attenuation defined in
CONFIG_AUDIO_ATTEN is applied over 24
bits with saturated rounding. Requires
CONFIG_16_BIT_CROP_EN to be 0.
D[7:4]
0x00F0
CONFIG_AUDIO_ATTEN
Attenuation in 6 dB steps.
D[9:8]
0x0300
CONFIG_JUSTIFY_RESOLUTION
Resolution of data on SD_IN, 00=16 bit,
01=20 bit, 10=24 bit, 11=Reserved. This is
required for right justified format and with left
justified LSB first.
D[10]
0x0400
CONFIG_16_BIT_CROP_EN
For 0, 17 bit SD_IN data is rounded down to
16 bits. For 1 only the most significant 16 bits
of data are received.
Table 19: PSKEY_DIGITAL_AUDIO_CONFIG