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AD1985

Rev. A | Page 31 of 48

Surround Volume Control Register (Index 0x38)

Reg Num

Name

D15 D14 D13 D12 D11 D10 D9

D6 D5

Default

0x38

Surround Volume

LSM X

LSR5 LSR4 LSR3 LSR2 LSR1 LSR0 RSM X

RSR5 RSR4 RSR3 RSR2 RSR1 RSR0 0x8080

This register controls the surround volume controls for both

stereo channels and mute bits. Each volume subregister contains

five bits, generating 32 volume levels with increments of 1.5 dB

each.

AC ’97 defines the 6-bit volume registers, therefore, to maintain

compatibility whenever the D5 or D13 bit is set to 1, its

respective lower five volume bits are automatically set to 1 by

the codec logic. On read-back, all lower five bits will read 1s

whenever these bits are set to 1.

Note that depending on the state of the AC97NC bit in

• For AC97NC = 0, the register controls the surround output

pin attenuators. The range is 0 dB to –46.5 dB.

• For AC97NC = 1, the register controls the surround DAC

gain/attenuators. The range is +12 dB to –34.5 dB.

RSR[5:0]

Right Surround Volume Control.

RSM

Right Surround Volume Mute. When this bit is set to 1, the right channel is muted.

LSR[5:0]

Left Surround Volume Control.

LSM

Left Surround Volume Mute. When this bit is set to 1, the left channel is muted.

xSR[5:0]

LSM (RSM)

Write

Readback

Function with AC97NC = 0

Function with AC97NC = 1

00 0000

0 dB Gain

+12 dB Gain

00 1111

−22.5 dB Gain

−10.5 dB Gain

01 1111

−46.5 dB Gain

−34.5 Gain

1x xxxx

01 1111

−46.5 dB Gain

Indeterminate1

xx xxxx

Muted, −∞ dB Gain

Note: x in the above table is a wild card, meaning the value has no effect.

1 When AC97NC is set to 1, there is only a 5-bit gain/attenuator to control, so the sixth bit, i.e., the MSB, does not control anything. Therefore, the 5-bit gain setting is

indeterminate, since the five LSBs are listed as wild cards.

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