cx25840 Conexant Systems, Inc., cx25840 Datasheet - Page 120

• Manufacturer Part Number: cx25840
• Description: Video Decoder And Broadcast Audio
• Manufacturer: Conexant Systems, Inc.

Detailed Functional Description
Figure 3-35. Right-Justified Audio
3.24.4
3.24.5
3-94
LRCK
SCK
SD
d1 d2
Serial Audio Output
AC’97 Interface
Figure 3-35
with the trailing edge of word select (default is rising edge), you must know how many
SA_BCLK_IN cycles per audio word are being input. For example 24 SA_BCLK_IN
cycles per audio word means SCK is 48x base audio rate, e.g., 48 bits x 48 kHz. Since
the audio input interface only supports 16-bit samples, SA_IN_BCNT_DEL would be
set to 8 to align the LSB with trailing edge of word select.
In addition, the audio input can act as a master or a slave device. Master or slave
mode is selected by the SA_IN_MASTER_MODE bit in the Serial Audio Input
Control2 (0x915) register. The pins used for serial clock and word select are therefore
bidirectional as they are inputs in slave, and outputs in master modes. As a master, the
device sources the clock (SA_CLK), and word select (SA_WCLK) signals. As a
target, the device expects to receive the SA_CLK and SA_WCLK from the external
audio source device.
Coarse gain control of the serial audio input is provided by bit-shifting the input data.
The audio samples can be shifted left or right by up to 3 bits, yielding gain or
attenuation of 6, 12, or 18 dB. This is controlled by the SA_IN_SHIFT field in the
Digital Audio Input Shifter (0x8CF) register.
The serial audio output interface is used to send demodulated and decoded 16-bit
audio streams to either high-fidelity audio DACs or some compression hardware (e.g.,
MPEG). The 16-bit samples will be output at a 32–96 kHz rate. The output format is
always 24 bits in master mode, and 16–32 bits in slave mode.
The AC’97 controller provides a digital data interface to a compatible AC_LINK
audio codec. The AC’97 specification has the following features: a fixed 48 kHz
sampling rate, 16-bit PCM data for left and right, third ADC input by way of 16-bit
PCM data for MIC, and GPIO control and status. The AC’97 audio codec performs
DAC and ADC conversions, mixing, and analog I/O for audio and always functions as
slave to the AC’97 digital controller that has been integrated into the CX25843/2/1/0.
The AC’97 audio codec communicates with the digital controller through the
d3 d4
bcnt_del: SCK Cycle
Right Justified Input
Delay Needed for
. . . .
gives an example of the right-justified mode. To set alignment of LSB
Conexant
dh
msb
msb
-1
msb
-2
.....
.....
lsb
CX25840/1/2/3 Data Sheet
102284B
102284_038
8/3/05