WM8740

Production Data

w

PD, Rev 4.4, April 2010

20

MUTE MODES

The device has various mute modes.

DIGITAL FILTER

ANALOGUE

ANRES

ANMUTE

Reg bit OPE = ‘1’

Unaffected

Asserted

MUTEB pin

Gain ramped to zero

On release volume ramps

to previous value

Asserted when

gain = 0

AUTOMUTE

(detect 1024 zero

input samples)

Automute has no effect on digital

filters

Asserted after

1024 zero input

samples if IZD = 1

Reg bit MUT

As MUTEB pin

As MUTEB pin

Gain = 00

(left and right)

Gain = -

∞dB

Asserted

RAM initialise

Gain initialised to 0dB

Asserted

Loss of system

clock

Not running (no clock). On clock

restart, filters initialised, RAM

initialised. Registers unchanged

Asserted

Asserted

No LRCLK or invalid

SCLK/LRCLK ratio

Filters initialised, RAM initialised.

Registers unchanged

Asserted

Asserted

RB

Reset – gain initialised to 0dB

Asserted

Asserted

Power-on reset

Reset

Asserted

Asserted

Table 20 Mute Modes

•

ANRES is the reset to the switched capacitor filter.

1.

ANMUTE is an analogue muting signal gating the analogue signal at the output (after

the SC filter)

2.

AUTOMUTE is asserted when both the IZD register bit is asserted and the input audio

data has been zero on both left and right channels for 1024 input samples. The first

non-zero sample de-asserts.

3.

Applying a logic low to MUTEB or setting MUT in Reg2 causes the gain registers to

ramp to zero. When a logic high is applied, the gain ramps slowly back up to the value

held in the appropriate attenuation register (AL or AR). The ramp rate = 128/fs s/0.5dB

step.

If SOFTMUTE is set or

MUTEB=0 then GAINL and

GAINR are overridden to 00

MUTEB

GAINL[0:7]

GAINR[0:7]

ANMUTE

SOFTMUTE

gain ramps between

previous and new gain

setting

Signal

Processing

IZD

ZERO

OPE

FREQ_INVALID

INIT

Automute:

Detect 1024

zero input

samples

Figure 11 Mute Modes