WM8728
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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)
10kΩ
SOFTMUTE
(Internal
Signal)
MUTEB
PIN
MUT (Register Bit)
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
24-bit right justified
0
0
1
0
1
0
20-bit right justified
16-bit I2S
24-bit I2S
1
1
Table 3 Input Format Selection
Note:
In 24 bit I2S mode, any width of 24 bits or less is supported provided that LRCIN is high for a
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
0
Off
On
1
Table 4 De-emphasis Control
WOLFSON MICROELECTRONICS LTD
PP Rev 1.2 April 2001
16
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
