WM8746

Production Data

w

March 2006, PD Rev 4.0

17

MUTE PIN

DESCRIPTION

0

Normal Operation

1

Mute all DAC channels

Floating

MUTE becomes an output to indicate when IZD occurs.

H = IZD detected (MUTE enabled)

L = IZD not detected (MUTE disabled)

A diagram showing how the various MUTE modes interact is shown below in Figure 11.

IZD (Register Bit)

AUTOMUTED (Internal

Signal)

10k

Ω

Ω

Ω

Ω

MUTE (Register Bit)

SOFTMUTE

(Internal

Signal)

MUTE

PIN

Figure 11 Selection Logic for MUTE Modes

The MUTE pin behaves as a bi-directional function, that is, as an input to select MUTE or NOT-

MUTE, or as an output indication of automute operation. MUTE is active high; taking the pin high

causes the filters to soft mute, ramping down the audio signal over a few milliseconds. Taking MUTE

low again allows data into the filter.

The automute function detects a series of zero value audio samples of 1024 samples long being

applied to all 6 channels. After such an event, a latch is set whose output (AUTOMUTED) is wire

OR’ed through a 10kohm resistor to the MUTE pin. Thus if the MUTE pin is not being driven, the

automute function will assert MUTE.

If MUTE is tied low, AUTOMUTED is overridden and will not mute. If MUTE is driven from a source

follower, or diode, then both MUTE and automute functions are available. If MUTE is not driven,

AUTOMUTED appears as a weak output (10k source impedance) so can be used to drive external

mute circuits. The automute signal is AND’ed with IZD, this qualified mute signal then being OR’ed

into the SOFTMUTE control. Therefore, in software mode, automute operation may be controlled with

the IZD control bit.

DE-EMPHASIS MODE

Setting the DEEMPH register bit puts all the digital filters into de-emphasis mode:

REGISTER ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

0000010

DAC Channel Control

1

DEEMPH

0

De-emphasis mode select:

0 : Normal Mode

1: De-emphasis Mode

Refer to Figure 18 - Figure 23 for details of the De-Emphasis filtering effects at different sample

rates.

In hardware mode (MODE=1) driving the MD/DM pin high has the same effect as setting the

DEEMPH bit:

MODE PIN

MD/DM PIN

DESCRIPTION

0

ignored

De-Emphasis controlled from DEEMPH register bit

1

0

Normal Mode

1

1

De-Emphasis Mode