LM4549 datasheet(16/18 Pages) NSC

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Application Information (Continued)

When the AC Link

″Codec Ready″ indicator bit (SDATA_IN

slot 0, bit 15) is a

″1″, it indicates that the AC Link and AC ’97

registers are in a fully operational state. The AC ’97 Control-

ler must further probe the Powerdown Control / Status Reg-

ister to determine exactly which subsections are ready.

BIT

Function

REF

Vref’s up to nominal level

ANL

Analog mixers ready

DAC

DAC section ready to accept data

ADC

ADC section ready to transmit data

Supported powerdown modes.

BIT

Function

PRO

PCM in ADC’s and Input Mux powerdown

PR1

PCM out DAC’s powerdown

PR2

Analog Mixer powerdown (VREF still on)

PR3

Analog Mixer powerdown (VREF off)

PR4

Digital Interface (AC Link) powerdown

(external clk off)

PR5

Internal Clk disable

PR6

not used

EAPD

External amplifier powerdown

Extended Audio ID Register (28h)

This read only register identifies which AC97 Extended Au-

dio features are supported. The LM4549 provides for VRA

(Variable Rate Audio) and Multiple Codec support. VRA is in-

dicated by a

″1″ in the LSB of register 28h. The two MSB’s,

ID1 and ID0, show the current codec configuration as con-

nected via external pins 45 and 46. Note that the external

logic connection to pins 45 and 46 are inverse in polarity to

the internal register setting.

Pin46 (ID1)

Pin45 (ID0)

Reg 28h ID1

Reg 28h ID0

Codec Mode

NC (not

connected)

NC (not

connected)

Primary

DVdd

Primary

DVdd

GND

Secondary 1

GND

DVdd

Secondary 2

GND

Secondary 3

Extended Audio Status/Control Register (2Ah)

This read/write register provides status and control of the

Variable Sample Rate function. Setting the LSB of this regis-

ter to

″1″ enables Variable Rate Audio (VRA) mode and al-

lows DAC and ADC sample rates to be programmed via reg-

isters 2Ch and 32h.

BIT

Function

VRA

0 = VRA off (48kHz fixed), 1 = VRA on

Sample Rate Control Registers (2Ch, 32h)

These read/write registers are used to set the sample rate

for the left and right channels of the DAC (2Ch) and the ADC

(32h). When Variable Rate Audio is enabled via bit-0 of Reg-

ister 2Ah, the sample rates can be programmed, in 1Hz in-

crements, to be any value from 4kHz to 48kHz. Below is a list

of the most common sample rates and their corresponding

SR15:SR0

Sample Rate (Hz)

1F40h

8000

2B11h

11025

3E80h

16000

5622h

22050

AC44h

44100

BB80h

48000

Reserved Registers

Do not write to these registers as they are reserved.

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