WM8904ECSSLASHR datasheet(76/188 Pages) WOLFSON

76 / 188 page

WM8904

Pre-Production

PP, Rev 3.3, September 2012

OUTPUT MUX CONTROL

By default, the DAC outputs are routed directly to the respective output PGAs. A multiplexer (mux) is

provided on each output path to select the BYPASSL or BYPASSR analogue signals from the

Left/Right Input PGAs in place of the DAC outputs.

The output multiplexers are configured using the register bits described in Table 44.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R61 (3Dh)

Analogue

OUT12 ZC

HPL_BYP_ENA

Selects input for left headphone

output MUX

0 = Left DAC

1 = Left input PGA (Analogue

bypass)

HPR_BYP_ENA

Selects input for right headphone

output MUX

0 = Right DAC

1 = Right input PGA (Analogue

bypass)

LINEOUTL_BYP_

ENA

Selects input for left line output

MUX

0 = Left DAC

1 = Left input PGA (Analogue

bypass)

LINEOUTR_BYP_

ENA

Selects input for right line output

MUX

0 = Right DAC

1 = Right input PGA (Analogue

bypass)

Table 44 Output Mux Control

OUTPUT VOLUME CONTROL

Each analogue output can be independently controlled. The headphone output control fields are

described in Table 45. The line output control fields are described in Table 46. The output pins are

described in more detail in “Analogue Outputs”.

The volume and mute status of each output can be controlled individually using the bit fields shown in

Table 45 and Table 46.

To prevent “zipper noise” when a volume adjustment is made, a zero-cross function is provided on all

output paths. When this function is enabled, volume updates will not take place until a zero-crossing

is detected. In the event of a long period without zero-crossings, a timeout will apply. The timeout

must be enabled by setting the TOCLK_ENA bit, as defined in “Clocking and Sample Rates”.

The volume update bits control the loading of the output driver volume data. For example, when

HPOUT_VU is set to 0, the headphone volume data can be loaded into the respective control

are updated when a 1 is written to HPOUT_VU. This makes it possible to update the gain of a

Left/Right pair of output paths simultaneously.

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