WM8736

Production Data

WOLFSON MICROELECTRONICS LTD

PD Rev 2.1 January 2001

10

HARDWARE CONTROL MODES

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

MUTE AND AUTOMUTE OPERATION

In both hardware and software modes 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.

IZD (Register Bit)

AUTOMUTED

(Internal Signal)

10k

Ω

MU (Register Bit)

SOFTMUTE

(Internal

Signal)

MUTE

PIN

Figure 6 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 both left and right 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 overidden 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 IZD

control bit.

I

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

input data word length, see Table 4. I

enough bit clocks are sent.

I

MC/IWL

INPUT DATA MODE

0

0

16-bit normal

0

1

20-bit normal

1

0

24-bit normal

11

I

Table 4 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

0

De-emphasis off

MD/DM

1

De-emphasis on

Table 5 De-emphasis Control