WM8904ECSSLASHR datasheet(135/188 Pages) WOLFSON

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Pre-Production

WM8904

PP, Rev 3.3, September 2012

135

QUICK START-UP AND SHUTDOWN

The WM8904 has the capability to perform a quick start-up and shutdown with a minimum number of

default start-up settings that set up the device for DAC playback via Headphone and Line output.

Assuming a 12.288MHz external clock, the start-up sequence configures the device for 48kHz

playback mode.

The default start-up sequence requires three register write operations. The default shutdown

sequence requires just a single register write. The minimum procedure for executing the quick start-

up and shutdown sequences is described below. See “Control Write Sequencer” for more details.

After the default start-up sequence has been performed, the DC offset correction values will be held

in memory, provided that power is maintained and a software reset is not performed. Fast start-up

using the stored values of DC offset correction is also possible, as described below.

QUICK START-UP (DEFAULT SEQUENCE)

An external clock must be applied to MCLK. Assuming 12.288MHz input clock, the start-up sequence

will take approximately 300ms to complete.

The following register operations will initiate the quick start-up sequence.

ADDRESS

VALUE

DESCRIPTION

R108 (6Ch)

Write Sequencer 0

0100h

WSEQ_ENA = 1

WSEQ_WRITE_INDEX = 00h

This enables the Write Sequencer

R111 (6Fh)

Write Sequencer 3

0100h

WSEQ_ABORT = 0

WSEQ_START = 1

WSEQ_START_INDEX = 00h

This starts the Write Sequencer at Index address 0 (00h)

R33 (21h)

DAC Digital 1

0000h

DAC_MONO = 0

DAC_SB_FILT = 0

DAC_MUTERATE = 0

DAC_UNMUTE_RAMP = 0

DAC_OSR128 = 0

DAC_MUTE = 0

DEEMPH = 00

This un-mutes the DACs

Table 91 Quick Start-up Control

The WSEQ_BUSY bit (in Register R112, see Table 85) will be set to 1 while the sequence runs.

When this bit returns to 0, the device has been set up and is ready for DAC playback operation.

FAST START-UP FROM STANDBY

The default start-up sequence runs the DC Servo to remove DC offsets from the outputs. The offset

for this path selection is then stored in memory. Provided that power is maintained to the chip, and a

software reset is not performed, then the DC offset correction will be held in memory on the WM8904.

This allows the DC Servo calibrations to be omitted from the start-up sequence if the offset correction

has already been performed. By omitting this part of the start-up sequence, a fast start-up time of less

than 50ms can be achieved.

The register write sequence described in Table 92 replaces the default DC Servo operation with

dummy operations, allowing a fast start-up to be achieved, assuming the device is initially in a

standby condition with DC offset correction previously performed.

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