CS4297
CrystalClear™ SoundFusion™ Audio Codec ’97
GENERAL DESCRIPTION
Overview
AC’97 Register Interface
The CS4297 implements the AC’97 Registers in
accordance with the AC’97 Specification. See the
Register Interface section for details on the
CS4297’s register set.
The CS4297 is a mixed-signal serial Codec based
on the AC’97 Specification. It is designed to be
paired with a digital controller, typically located on
the PCI bus. The AC’97 Controller is responsible
for all communications between the CS4297 and
the rest of the system. The CS4297 functions as an
analog mixer, a stereo ADC, a stereo DAC, and a
control and digital audio stream interface to the
AC’97 Controller.
Power Management
The CS4297 supports a number of different power
down modes. They are accessed through register
0x26h of the CS4297 register interface. Please refer
to the Power Management section of the data sheet.
Analog Section
The CS4297 contains two distinct functional sec-
tions: Digital and Analog. The Digital section in- Please refer to Figure 1, Mixer diagram, for a high
cludes the AC-Link registers, power management
support, SYNC detection circuitry, and AC-Link
serial port interface logic. The Analog section in-
cludes the analog input multiplexor (mux), stereo
output mixer, mono output mixer, stereo ADCs,
stereo DACs, and analog volume controls.
level graphical representation of the CS4297 ana-
log mixer structure.
Output Mixer
There are two output mixers on the CS4297. The
stereo output mixer sums together the analog inputs
to the CS4297 according to the settings in the vol-
ume control registers. The mono output mixer gen-
erates a monophonic sum of the left and right
channels from the stereo output mixer. However,
the mono output mixer does not include the
PC_BEEP and PHONE signals which are included
in the stereo output mix. The stereo output mix is
sent to the LINE_OUT and ALT_LINE_OUT out-
put pins of the CS4297. The mono output mix is
sent to the MONO_OUT output pin on the CS4297.
Digital Section
AC-Link
The AC-Link is the 5-wire digital interface to the
AC’97 Controller chip. The CS4297 generates the
BIT_CLK and the SDATA_IN signals. The AC’97
Controller must drive the SYNC, SDATA_OUT
and RESET# signals. Please refer to the AC-Link
timing section for the timing characteristics of the
interface. The interface uses the SYNC signal,
which is synchronous with BIT_CLK, to align the
data within the frame. The AC-Link signals may be
referenced to either 5 Volts or 3.3 Volts. The
CS4297 should use the same digital supply voltage
as the AC’97 Controller chip.
Input Mux
The input multiplexor controls which analog input
is sent to the ADCs. The output of the input mux is
converted to stereo 18-bit digital PCM data and
sent to the AC’97 Controller chip in Slots 3 and 4
of the AC-Link SDATA_IN signal.
Volume Control
The volume control registers of the AC’97 Register
interface control analog input level to the input
mixer, the master volume level, and the alternate
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DS242F5
CIRRUS [ CIRRUS LOGIC ]
