WM8728

Product Preview

WOLFSON MICROELECTRONICS LTD

PP Rev 1.2 April 2001

16

Figure 12 Application and Release of Soft Mute

The MUTEB pin is an input to select mute or not mute. MUTEB is active low; taking the pin low

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

MUTEB high again allows data into the filter.

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

being applied to both channels. After such an event, a latch is set whose output (AUTOMUTED)

is wire OR’ed through a 10kohm resistor to the MUTEB pin. Thus if the MUTEB pin is not being

driven, the automute function will assert mute.

If MUTEB is tied high, AUTOMUTED is overridden and will not mute unless the IZD register bit is

set. If MUTEB is driven from a bi-directional source, then both MUTE and automute functions are

available. If MUTEB is not driven, AUTOMUTED appears as a weak output (10kOhm-source

impedance) so can be used to drive external mute circuits. AUTOMUTED will be removed as

soon as any channel receives a non-ZERO input.

A diagram showing how the various Mute modes interact is shown below Figure 13.

IZD (Register Bit)

AUTOMUTED

(Internal Signal)

10k

Ω

MUT (Register Bit)

SOFTMUTE

(Internal

Signal)

MUTEB

PIN

Figure 13 Selection Logic for MUTE Modes

INPUT FORMAT SELECTION

In hardware mode, LATI2S (pin 20) and CSBIWL (pin 15) become input controls for selection of

input data format type and input data word length.

LATI2S

CSBIWL

INPUT DATA MODE

00

24-bit right justified

01

20-bit right justified

10

16-bit I

11

24-bit I

Table 3 Input Format Selection

Note:

In 24 bit I

minimum of 24 BCKINs and low for a minimum of 24 BCKINs. If exactly 32 BCKINs occur in one

LRCIN (16 high, 16 low) the chip will auto detect and run a 16 bit data mode.

DE-EMPHASIS CONTROL

In hardware mode, SDIDEM (pin 18) becomes an input control for selection of de-emphasis

filtering to be applied.

SDIDEM

DE-EMPHASIS

0Off

1On

Table 4 De-emphasis Control