AD1981B
Headphones Volume Register (Index 04h)
Reg
No. Name
D15
D14
D13
X
D12
LHV
4
D11
LHV
3
D10
LHV
2
D9
LHV
1
D8
LHV
0
D7
RM*
D6
X
D5
X
D4
RHV
4
D3
RHV
3
D2
RHV
2
D1
RHV
1
D0
RHV
0
Default
8000h
04h Headphone HPM X
Volume
*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]
RM
LHV [4:0]
HPM
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.
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.
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.
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
Reg. 76h
MSPLT*
0
0
0
0
0
1
1
1
0
0
0
0
1
0
1
1
D15 WRITE
00 0000
00 1111
01 1111
1x xxxx
xx xxxx
1x xxxx
xx xxxx
xx xxxx
Control Bits
Master Volume (02h) and Headphone Volume (04h)
Left Channel Volume D[13:8]
READBACK Function
00 0000
00 1111
01 1111
01 1111
xx xxxx
01 1111
xx xxxx
xx xxxx
0 dB Gain
–22.5 dB Gain
–46.5 dB Gain
–46.5 dB Gain
– dB Gain, Muted
–46.5 dB Gain
– dB Gain, Left Only Muted
– dB Gain, Left Muted
D7*
x
x
x
x
x
1
0
1
Right Channel Volume D[5:0]
WRITE READBACK
00 0000
00 1111
01 1111
1x xxxx
xx xxxx
xx xxxx
xx xxxx
xx xxxx
00 0000
00 1111
01 1111
01 1111
xx xxxx
xx xxxx
xx xxxx
xx xxxx
Function
0 dB Gain
–22.5 dB Gain
–46.5 dB Gain
–46.5 dB Gain
– dB Gain, Muted
– dB Gain, Right
Only Muted
–46.5 dB Gain
– 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.
REV. B
–11–
AD [ ANALOG DEVICES ]
