CS4297 datasheet(15/46 Pages) CIRRUS

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DS242F5

CS4297

CrystalClear™ SoundFusion™ Audio Codec ’97

DIGITAL HARDWARE DESCRIPTION

AC’97 AC-Link

The AC-Link is the serial connection between the

AC’97 Controller and the CS4297. The interface

consists of 5 signal lines (2 data, 2 clocks, and 1 re-

set). The basic connections of the link are shown in

Figure 2. The signals will be explained in detail be-

low.

AC-Link Protocol

The CS4297 serial interface is designed according

to the AC’97 Specification to allow connection to

any AC’97 Controller. An AC-Link audio frame is

divided into 13 ‘slots’; 1 16-bit slot and 12 20-bit

slots. During each audio frame, data is passed bi-di-

rectionally between the CS4297 and the AC’97

Controller.

AC-Link Serial Data Output Frame

For the serial data output frame, the SYNC,

BIT_CLK, and SDATA_OUT signals are used. In

the serial data output frame, data is passed on the

SDATA_OUT pin FROM the AC’97 Controller

TO the CS4297. In Figure 3 and in the following

Frame Slot definitions, the position of each bit lo-

cation within the frame is noted. The first bit posi-

tion in a new serial data frame is F0 and the last bit

position in the serial data frame is F255.

When SYNC goes active (high) and is sampled ac-

tive by the CS4297 (on the falling edge of

BIT_CLK), both devices are synchronized to a new

serial data frame. The data on the SDATA_OUT

pin at this clock edge is the final bit of the previous

serial data frame’s data. On the next rising edge of

BIT_CLK, the first bit of slot 0 is driven by the

AC’97 Controller on the SDATA_OUT pin. The

CS4297 latches in this data, as the first bit of the

frame, on the next falling edge of the BIT_CLK

clock signal.

Digital AC’97

Controller

CS4297

SYNC

BIT_CLK

SDATA_OUT

SDATA_IN

RESET#

Figure 2. AC-link Connections

20.8uS

(48 KHz)

Tag Phase

Data Phase

12.288 MHz

81.4 nS

SYNC

BIT_CLK

SDATA_OUT

SDATA_IN

F16

F15

F14

F13

F12

F36

F56

F76

F255

Valid

Frame

Slot 1

Valid

Slot 2

Valid

R/W

WD15

WD14

F37

F57

LP17

LP16

RP17

LC17

LC16

RC17

RD15

RD14

Codec

Ready

Slot 1

Valid

Slot 2

Valid

Bit Frame

Position

F16

F15

F14

F13

F12

F36

F56

F76

F255

F37

F57

Bit Frame

Position

F255

F97

Slot 0

Slot 1

Slot 2

Slot 3

Slot 4

Slots 5-12

Figure 3. AC-Link Input and Output Framing

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