WM8728
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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
0000
[7:0]
LAT[7:0]
11111111 (0dB)
Attenuation data for Left channel DACL in 0.5dB steps.
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.
Attenuation data for Right channel DACR in 0.5dB steps.
0001
[7:0]
8
RAT[7:0]
11111111 (0dB)
0
Attenuation
DACR
UPDATER
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 8 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)
FF(hex)
0.5dB
0dB
Table 9 Attenuation Control Levels
MUTE MODES
Setting the MUT register bit will apply a ’soft’ mute to the input of the digital filters:
REGISTER ADDRESS
0010
BIT
LABEL
DEFAULT
DESCRIPTION
Soft Mute select
0
MUT
0
DAC Control
0 : Normal Operation
1: Soft mute all channels
Table 10 Mute control
WOLFSON MICROELECTRONICS LTD
PP Rev 1.2 April 2001
19
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
