WM8746

Production Data

w

March 2006, PD Rev 4.0

21

HARDWARE CONTROL MODES

When the MODE pin is held high the following hardware modes of operation are available.

MUTE AND AUTOMUTE OPERATION

Pin 9 (MUTE) controls selection of MUTE directly, and can be used to enable and disable the

automute function, or as an output of the automuted signal.

AUTOMUTED (Internal

Signal)

10k

Ω

Ω

Ω

Ω

SOFTMUTE

(Internal

Signal)

MUTE

PIN

Figure 12 Mute Circuit Operation

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.

ML/I2S AND MC/IWL INPUT FORMAT SELECTION

In hardware mode, pins 12 and 13 become input controls for selection of input data format type and

input data word length, see Table 5. I

enough bit clocks are sent.

ML/I2S

MC/IWL

INPUT DATA MODE

0

0

16-bit right justified

0

1

20-bit right justified

1

0

24-bit right justified

1

1

I

Table 9 Control of Input Data Format Type and Input Data Word Length

MD/DM DE-EMPHASIS

In hardware mode, pin 14 becomes an input control for selection of de-emphasis filtering to be

applied. See Table 5.

MD/DM

DE-EMPHASIS MODE

0

De-emphasis off

1

De-emphasis on

Table 10 De-emphasis Control