LM4549B datasheet(22/28 Pages) NSC

22 / 28 page

Default settings are indicated by *.

RESET REGISTER (00h)

Writing any value to this register causes a Register Reset

which changes all registers back to their default values. If a

read is performed on this register, the LM4549B will return a

value of 0D40h. This value can be interpreted in accordance

with the AC ’97 Specification to indicate that National 3D

Sound is implemented and 18-bit data is supported for both

the ADCs and DACs.

MASTER VOLUME REGISTER (02h)

This output register allows the output level from either chan-

nel of the stereo LINE_OUT to be muted or attenuated over

the range 0 dB – 46.5 dB in nominal 1.5 dB steps. There are

6 bits of volume control for each channel and both stereo

channels can be individually attenuated. The mute bit (D15)

acts simultaneously on both stereo channels of LINE_OUT.

The AC’97 specification states that “support for the MSB of

the level is optional.” All six bits may be written to the

whether the MSB is supported or not.

Mute

Mx5:Mx0

Function

0 00000

0 dB attenuation

0 11111

46.5 dB attenuation

1 xxxxx

As Written

0 11111

As read back

X XXXXX

*mute

Default: 8000h

LINE LEVEL VOLUME REGISTER (04h)

This output register allows the level from both channels of

LNLVL_OUT to be muted or individually attenuated over the

range 0 dB to –46.5 dB in nominal 1.5 dB steps. There are 6

bits of volume control for each channel plus one mute bit.

The mute bit (D15) acts on both channels. Operation of this

MONO VOLUME REGISTER (06h)

This output register allows the level from MONO_OUT to be

muted or attenuated over the range 0 dB – 46.5 dB in

nominal 1.5 dB steps. There are 6 bits of volume control and

one mute bit (D15). All six bits may be written to the register,

but if the MSB is a 1, the MSB is ignored and the register will

be set to 0 11111. This will be the value when the register is

read, allowing the software driver to detect whether the MSB

is supported or not.

Mute

MM5:MM0

Function

0 00000

0 dB attenuation

0 11111

46.5 dB attenuation

1 xxxxx

As written

0 11111

As read back

X XXXXX

*mute

Default: 8000h

PC BEEP VOLUME REGISTER (0Ah)

This input register adjusts the level of the mono PC_BEEP

input to the stereo mixer MIX2 where it is summed equally

into both channels of the Stereo Mix signal. PC_BEEP can

be both muted and attenuated over a range of 0 dB to –45

dB in nominal 3 dB steps. Note that the default setting for the

PC_Beep Volume register is 0 dB attenuation rather than

mute.

Mute

PV3:PV0

Function

0000

*0 dB attenuation

1111

45 dB attenuation

XXXX

mute

Default: 0000h

MIXER INPUT VOLUME REGISTERS (Index 0Ch - 18h)

These input registers adjust the volume levels into the stereo

mixers MIX1 and MIX2. Each channel may be adjusted over

a range of +12 dB gain to –34.5 dB attenuation in 1.5 dB

steps. For stereo ports, volumes of the left and right chan-

nels can be independently adjusted. Muting a given port is

accomplished by setting the MSB to 1. Setting the MSB to 1

for stereo ports mutes both the left and right channels. The

Mic Volume register (0Eh) controls an additional 20 dB boost

for the selected microphone input by setting the 20dB bit

(D6).

Mute

Gx4:Gx0

Function

0 0000

+12 dB gain

0 1000

0 dB gain

1 1111

–34.5 dB attenuation

X XXXX

*mute

Default:

8008h (mono registers)

8808h (stereo registers)

RECORD SELECT REGISTER (1Ah)

This register independently controls the sources for the right

and left channels of the stereo ADC. The default value of

0000h corresponds to selecting the (mono) Mic input for both

channels.

SL2:SL0

Source for Left Channel ADC

*Mic input

CD input (L)

VIDEO input (L)

AUX input (L)

LINE_IN input (L)

Stereo Mix (L)

Mono Mix

PHONE input

SR2:SR0

Source for Right Channel ADC

*Mic input

CD input (R)

VIDEO input (R)

AUX input (R)

LINE_IN input (R)

Stereo Mix (R)

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