AD1981B

Rev. C | Page 14 of 32

HEADPHONE VOLUME REGISTER

Index 0x04

This register controls the headphone volume controls for both stereo channels and the 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 automatically set to 1 by the codec logic. On readback,

all lower five bits read 1s whenever these bits are set to 1. Refer to Table 12 for examples.

Reg

No.

Name

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

Default

0x04

Headphone

Volume

HPM

X

X

LHV4

LHV3

LHV2

LHV1

LHV0

RM1

X

X

RHV4

RHV3

RHV2

RHV1

RHV0

0x8000

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

Table 11.

Bit

Mnemonic

Function

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 0x76, this bit mutes the right channel separately from the

HPM bit. Otherwise, this bit always reads 0 and has 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

Headphone Volume

Mute

When this bit is set to 1, both the left and right channels are muted, unless the MSPLT bit in

Register 0x76 is set to 1, in which case this mute bit affects only the left channel.

Table 12. Volume Settings for Master and Headphone

Reg. 0x76

Control Bits Master Volume (0x02) and Headphone Volume (0x04)

Left-Channel Volume D [13:8]

Right-Channel Volume D [5:0]

MSPLT1

D15

Write

Readback

Function

D71

Write

Readback

Function

0

0

00 0000

00 0000

0 dB Gain

X

00 0000

00 0000

0 dB Gain

0

0

00 1111

00 1111

−22.5 dB Gain

X

00 1111

00 1111

−22.5 dB Gain

0

0

01 1111

01 1111

−46.5 dB Gain

X

01 1111

01 1111

−46.5 dB Gain

0

0

1X XXXX

01 1111

−46.5 dB Gain

X

1X XXXX

01 1111

−46.5 dB Gain

0

1

XX XXXX

XX XXXX

−∞ dB Gain, Muted

X

XX XXXX

XX XXXX

−∞ dB Gain, Muted

1

0

1X XXXX

01 1111

−46.5 dB Gain

1

XX XXXX

XX XXXX

−∞ dB Gain, Right Only Muted

1

1

XX XXXX

XX XXXX

−∞ dB Gain, Left Only Muted

0

XX XXXX

XX XXXX

−46.5 dB Gain

1

1

XX XXXX

XX XXXX

−∞ dB Gain, Left Muted

1

XX XXXX

XX XXXX

−∞ dB Gain, Right Muted

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

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