WM8756 datasheet(25/39 Pages) WOLFSON

25 / 39 page

WM8756

Advance Information

AI Rev 1.3 October 2001

HARDWARE CONTROL MODES

When the MODE pin is held high, and DSDB pin is high, the following hardware modes of operation are

available.

MUTE AND AUTOMUTE OPERATION

In both hardware and software modes pin 12 (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

SOFTMUTE

(Internal

Signal)

MUTE

Figure 14 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.

INPUT FORMAT SELECTION

In hardware mode, pins 16 and 17 become input controls for selection of input data format type and input

data word length (see Table 16). I

2S mode is designed to support any word length provided enough bit

clocks are sent.

ML/I2S

MC/IWL

INPUT DATA MODE

16-bit right justified

20-bit right justified

24-bit right justified

2S mode

Table 16 Control of Input Data Format Type and Input Data Word Length

MD/DM DE-EMPHASIS

In hardware mode, pin 18 becomes an input control for selection of de-emphasis filtering to be applied

(see Table 17).

MD/DM

DE-EMPHASIS MODE

De-emphasis off

De-emphasis on

Table 17 De-emphasis Control

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