CS4297 datasheet(12/46 Pages) CIRRUS

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DS242F5

CS4297

CrystalClear™ SoundFusion™ Audio Codec ’97

GENERAL DESCRIPTION

Overview

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.

The CS4297 contains two distinct functional sec-

tions: Digital and Analog. The Digital section in-

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.

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.

AC’97 Register Interface

The CS4297 implements the AC’97 Registers in

accordance with the AC’97 Specification. See the

CS4297’s register set.

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

Please refer to Figure 1, Mixer diagram, for a high

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.

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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