WM8728

Production Data

w

PD Rev 4.2 April 2004

20

ATTENUATION CONTROL

Each DAC channel can be attenuated digitally before being applied to the digital filter. Attenuation

is 0dB by default but can be set between 0 and 127.5dB in 0.5dB steps using the 8 Attenuation

control bits. All attenuation registers are double latched allowing new values to be pre-latched to

both channels before being updated synchronously. Setting the UPDATE bit on any attenuation

write will cause all pre-latched values to be immediately applied to the DAC channels.

REGISTER

ADDRESS

BITS

LABEL

DEFAULT

DESCRIPTION

[7:0]

LAT[7:0]

11111111 (0dB)

Attenuation data for Left channel DACL in 0.5dB steps.

0000

Attenuation

DACL

8

UPDATEL

0

Controls simultaneous update of all Attenuation Latches

0: Store DACL in intermediate latch (no change to output)

1: Store DACL and update attenuation on all channels.

[7:0]

RAT[7:0]

11111111 (0dB)

Attenuation data for Right channel DACR in 0.5dB steps.

0001

Attenuation

DACR

8

UPDATER

0

Controls simultaneous update of all Attenuation Latches

0: Store DACR in intermediate latch (no change to output)

1: Store DACR and update attenuation on all channels.

Table 9 Attenuation Register Map

Note:

1.

The UPDATE bit is not latched. If UPDATE=0, the Attenuation value will be written to the pre-latch but not applied to the

relevant DAC. If UPDATE=1, all pre-latched values and the current value being written will be applied on the next input

sample.

2.

Care should be used in reducing the attenuation as rapid large volume changes can introduce zipper noise.

DAC OUTPUT ATTENUATION

Registers LAT and RAT control the left and right channel attenuation. Table 9 shows how the

attenuation levels are selected from the 8-bit words.

XAT[7:0]

ATTENUATION LEVEL

00(hex)

∞dB (mute)

01(hex)

127.5dB

:

:

:

:

:

:

FE(hex)

0.5dB

FF(hex)

0dB

Table 10 Attenuation Control Levels

MUTE MODES

Setting the MUT register bit will apply a 'soft' mute to the input of the digital filters:

REGISTER ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

0010

DAC Control

0

MUT

0

Soft Mute select

0 : Normal Operation

1: Soft mute all channels

Table 11 Mute control