62
DS726PP2
CS4525
6.6
Serial Audio Interfaces
The CS4525 interfaces to external digital audio devices via the serial audio input port and the auxiliary/delay
serial ports.
The serial audio input port provides support for I²S, Left-Justified and Right-Justified data formats and op-
erates in slave mode only, with LRCK and SCLK as inputs. The input LRCK signal must be equal to the
sample rate, Fs and must be synchronous to the serial bit clock, SCLK, which is used to sample the data
bits.
The auxiliary/delay serial port (available in software mode only) supports I²S and Left-Justified data formats
and operates in master mode only, with AUX_LRCK and AUX_SCLK as outputs.
Each of the supported formats is described in detail in sections
below. Please refer to the
Audio Input Port Switching Specifications
and
AUX Serial Audio I/O Port Switching Specifications
on
(respectively) for the precise timing and tolerances of each signal.
For additional information, application note AN282 presents a tutorial of the 2-channel serial audio interface.
AN282 can be downloaded from the Cirrus Logic web site at
.
6.6.1
I²S Data Format
In I²S format, data is received most significant bit first one SCLK delay after the transition of LRCK and is
valid on the rising edge of SCLK. The left channel data is presented when LRCK is low; the right channel
data is presented when LRCK is high.
6.6.2
Left-Justified Data Format
In Left-Justified format, data is received most significant bit first on the first SCLK after a LRCK transition
and is valid on the rising edge of SCLK. The left channel data is presented when LRCK is high and the
right channel data is presented when LRCK is low.
Left Channel
Right Channel
SDIN
+3 +2 +1
+5 +4
-1 -2 -3 -4 -5
+3 +2 +1
+5 +4
-1 -2 -3 -4
MSB
MSB
LSB
LSB
LRCK
SCLK
Figure 30. I²S Serial Audio Formats
LRCK
SCLK
Left Channel
Right Channel
SDIN
+3 +2 +1
+5 +4
-1 -2 -3 -4 -5
+3 +2 +1
+5 +4
-1 -2 -3 -4
MSB
LSB
MSB
LSB
Figure 31. Left-Justified Serial Audio Formats