REV. B

AD1981B

–11–

Headphones Volume Register (Index 04h)

*For AC ’97 compatibility, Bit D7 (RM) is available only by setting the MSPLT bit, Register 76h. The MSPLT bit enables separate mute bits for the left and right

channels. If MSPLT is not set, RM bit has no effect. All registers not shown and bits containing an X are assumed to be reserved.

Refer to Table I for examples. This register controls the headphone volume controls for both stereo channels and mute bit. Each

volume subregister contains five bits, generating 32 volume levels with 31 steps of 1.5 dB each. Because AC ’97 defines 6-bit volume

registers, to maintain compatibility, whenever the D5 or D13 bits are set to 1, their respective lower five volume bits are automati-

cally set to 1 by the codec logic. On readback, all lower five bits will read 1s whenever these bits are set to 1.

RHV [4:0]

Right Headphone Volume Control. The least significant bit represents 1.5 dB. This register controls the output

from 0 dB to a maximum attenuation of 46.5 dB.

RM

Right Channel Mute. Once enabled by the MSPLT bit in Register 76h, this bit mutes the right channel separately

from the HPM bit. Otherwise, this bit will always read 0 and will have no effect when set to 1.

LHV [4:0]

Left Headphone Volume Control. The least significant bit represents 1.5 dB. This register controls the output

from 0 dB to a maximum attenuation of 46.5 dB.

HPM

Headphones Volume Mute. When this bit is set to 1, both the left and right channels are muted, unless the

MSPLT bit in Register 76h is set to 1, in which case this mute bit will affect only the left channel.

Table I. Volume Settings for Master and Headphone

Control Bits

Reg. 76h

Master Volume (02h) and Headphone Volume (04h)

MSPLT

*

Left Channel Volume D[13:8]

Right Channel Volume D[5:0]

D15 WRITE

READBACK Function

D7

*

WRITE

READBACK

Function

00

00 0000

00 0000

0 dB Gain

x

00 0000

00 0000

0 dB Gain

00

00 1111

00 1111

–22.5 dB Gain

x

00 1111

00 1111

–22.5 dB Gain

00

01 1111

01 1111

–46.5 dB Gain

x

01 1111

01 1111

–46.5 dB Gain

00

1x xxxx

01 1111

–46.5 dB Gain

x

1x xxxx

01 1111

–46.5 dB Gain

01

xx xxxx

xx xxxx

–

dB Gain, Muted

x

xx xxxx

xx xxxx

–

dB Gain, Muted

10

1x xxxx

01 1111

–46.5 dB Gain

1

xx xxxx

xx xxxx

–

dB Gain, Right

Only Muted

11

xx xxxx

xx xxxx

– dB Gain, Left Only Muted

0

xx xxxx

xx xxxx

–46.5 dB Gain

11

xx xxxx

xx xxxx

–

dB Gain, Left Muted

1

xx xxxx

xx xxxx

–

dB Gain, Right

Muted

*For AC ’97 compatibility, Bit D7 (RM) is available only by setting the MSPLT bit, Register 76h. The MSPLT bit enables separate mute bits for the left and right

channels. If MSPLT is not set, RM bit has no effect.

X in the above table is a wild card and has no effect on the value.

Reg

No. Name

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

Default

04h Headphone HPM

X

X

LHV

LHV

LHV

LHV

LHV

RM

*

XXRHV

RHV

RHV

RHV

RHV

8000h

Volume

4

3

2

1

0

4

3

2

1

0