WM8740
Production Data
MUTE MODES
The device has various mute modes.
DIGITAL FILTER
ANALOGUE
ANRES
ANMUTE
Reg bit OPE = ‘1’
MUTEB pin
Unaffected
Asserted
Gain ramped to zero
Asserted when
gain = 0
On release volume ramps
to previous value
AUTOMUTE
Automute has no effect on digital
filters
Asserted after
1024 zero input
samples if IZD = 1
(detect 1024 zero
input samples)
Reg bit MUT
As MUTEB pin
As MUTEB pin
Asserted
Gain = 00
Gain = -∞dB
(left and right)
RAM initialise
Gain initialised to 0dB
Asserted
Asserted
Loss of system
clock
Not running (no clock). On clock
restart, filters initialised, RAM
initialised. Registers unchanged
Asserted
Asserted
No LRCLK or invalid
SCLK/LRCLK ratio
Filters initialised, RAM initialised.
Registers unchanged
Asserted
RB
Reset – gain initialised to 0dB
Reset
Asserted
Asserted
Asserted
Asserted
Power-on reset
Table 20 Mute Modes
ANRES is the reset to the switched capacitor filter.
1. ANMUTE is an analogue muting signal gating the analogue signal at the output (after
the SC filter)
2. AUTOMUTE is asserted when both the IZD register bit is asserted and the input audio
data has been zero on both left and right channels for 1024 input samples. The first
non-zero sample de-asserts.
3. Applying a logic low to MUTEB or setting MUT in Reg2 causes the gain registers to
ramp to zero. When a logic high is applied, the gain ramps slowly back up to the value
held in the appropriate attenuation register (AL or AR). The ramp rate = 128/fs s/0.5dB
step.
If SOFTMUTE is set or
MUTEB=0 then GAINL and
GAINR are overridden to 00
GAINL[0:7]
Signal
Processing
GAINR[0:7]
SOFTMUTE
MUTEB
gain ramps between
previous and new gain
setting
Automute:
Detect 1024
zero input
samples
IZD
OPE
FREQ_INVALID
INIT
ANMUTE
ZERO
Figure 7 Mute Modes
PD Rev 4.0 April 2004
17
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
