WM8746 Wolfson Microelectronics plc, WM8746 Datasheet - Page 21

• Manufacturer Part Number: WM8746
• Description: 24-bit, 192khz 6-channel Dac With Volume Control
• Manufacturer: Wolfson Microelectronics plc

WM8746
HARDWARE CONTROL MODES
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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.
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.
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.
Table 10 De-emphasis Control
AUTOMUTED (Internal
MD/DM
ML/I2S
0
0
1
1
0
1
Signal)
MUTE
PIN
10kΩ
DE-EMPHASIS MODE
2
S mode is designed to support any word length provided
De-emphasis off
De-emphasis on
MC/IWL
0
1
0
1
PD, October 2008, Rev 4.2
INPUT DATA MODE
16-bit right justified
20-bit right justified
24-bit right justified
I
2
S mode
SOFTMUTE
(Internal
Signal)
Production Data
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