TAS1020A Datasheet, PDF (55/114 Pages) Texas Instruments – USB Streaming Controller

TAS1020A
Serial Input Data
MCLKO
CSYNC
CSCLK
CDATO
CDATI
CRESET
CSCHNE
AC’97 IC
AC97CLK
SYNC
BIT_CLK
SDATA_IN
SDATA_OUT
CRESET
Primary
AC97 or MC97
AC97CLK
SYNC
BIT_CLK
SDATA_IN
SDATA_OUT
CRESET
Secondary
Figure 2–10. Connection of the TAS1020A to Multiple AC ’97 Codecs
2.2.13.4 Inter-IC Sound (I²S) Modes of Operation
The TAS1020A offers two I²S modes of operation, codec port interface mode 4 and codec port interface mode 5. The
difference in the I²S modes is the number of serial data outputs and/or serial data inputs supported. For codec port
interface mode 4, there is one serial data output (SDOUT1) and two serial data inputs (SDIN1, SDIN2). Hence, mode
4 can be used to connect the TAS1020A device to a codec with one stereo DAC and two ADCs. For codec port
interface mode 5, one serial data output (SDOUT1) and one serial data input (SDIN2) are supported, but these data
streams can be completely independent as each is assigned its separate sync pulse and bit clock. Mode 5 then can
service applications that require different sampling rates for record and playback. Table 2–6 shows the TAS1020A
codec terminal assignments and the respective signal names for each of the I²S modes. Figure 2–7 shows the signal
waveforms for I²S.
Table 2–6. Terminal Assignments for Codec Port Interface I²S Modes
TERMINAL
NO.
NAME
I2S
MODE 4
I2S
MODE 5
35 CSYNC
LRCK
O LRCK1
O
37 CSCLK
SCLK
O SCLK1
O
38 CDATO
SDOUT1
O SDOUT1
O
36 CDATI
SDIN1
I SDIN2
I
34 CRESET
CRESET
O SCLK2
O
32 CSCHNE
SDIN2
I LRCK2
O
In all I²S modes, the codec port interface is configured as a bidirectional full duplex serial interface with two time slots
per frame. The frame sync signal is the left/right clock (LRCK) signal. Time slot 0 is used for the left channel audio
data, and time slot 1 is used for the right channel audio data. Both time slots must be set to 32 serial clock (SCLK)
cycles in length giving an SCLK-to-LRCK ratio of 64. The serial clock frequency is based on the audio sample rate.
For example, when using an audio sample rate (FS) of 48 kHz, the SCLK frequency must be set to 3.072 MHz
(64×FS). (Note that the terms codec frame sync, audio sample rate (FS), and LRCK all refer to the same signal.)
The LRCK signal has a 50% duty cycle. The LRCK signal is low for the left channel time slot and is high for the right
channel time slot. In addition, the LRCK signal is synchronous to the falling edge of the SCLK. Serial data is shifted
out on the falling edge of SCLK and shifted in on the rising edge of SCLK. Both for the left channel and the right
channel, there is a one-SCLK cycle delay from the edge of LRCK before the most significant bit of the data is shifted
out.
For the I²S modes of the codec port interface, there is a 24-bit transmit and 24-bit receive shift register for each
SDOUT and SDIN signal, respectively. As a result, the interface can actually support 16-bit, 18-bit, 20-bit or 24-bit
transfers. The interface pads the unused bits automatically with zeros.
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