WM8746 Wolfson Microelectronics plc, WM8746 Datasheet - Page 17

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

WM8746
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A diagram showing how the various MUTE modes interact is shown below in Figure 11.
Figure 11 Selection Logic for MUTE Modes
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. 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
the IZD control bit.
DE-EMPHASIS MODE
Setting the DEEMPH register bit puts all the digital filters into de-emphasis mode:
Refer to Figure 18 - Figure 23 for details of the De-Emphasis filtering effects at different sample
rates.
In hardware mode (MODE=1) driving the MD/DM pin high has the same effect as setting the
DEEMPH bit:
0000010
DAC Channel Control
REGISTER ADDRESS
MODE PIN
AUTOMUTED (Internal
MUTE PIN
MUTE (Register Bit)
Floating
0
1
1
0
1
IZD (Register Bit)
MD/DM PIN
Signal)
MUTE
ignored
Normal Operation
Mute all DAC channels
MUTE becomes an output to indicate when IZD occurs.
H = IZD detected (MUTE enabled)
L = IZD not detected (MUTE disabled)
PIN
0
1
BIT
1
DEEMPH
LABEL
10kΩ
De-Emphasis controlled from DEEMPH register bit
Normal Mode
De-Emphasis Mode
DEFAULT
0
DESCRIPTION
DESCRIPTION
De-emphasis mode select:
0 : Normal Mode
1: De-emphasis Mode
DESCRIPTION
PD, October 2008, Rev 4.2
Production Data
SOFTMUTE
(Internal
Signal)
17