wm8918 Wolfson Microelectronics plc, wm8918 Datasheet - Page 68

• Manufacturer Part Number: wm8918
• Description: Ultra Low Power Dac For Portable Audio Applications
• Manufacturer: Wolfson Microelectronics plc

WM8918
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OUTPUT MUX CONTROL
By default, the DAC outputs are routed directly to the respective output PGAs. A multiplexer (mux) is
provided on each output path to select the BYPASSL or BYPASSR analogue signals from the
Left/Right Input PGAs in place of the DAC outputs.
The output multiplexers are configured using the register bits described in Table 42.
Table 42 Output Mux Control
OUTPUT VOLUME CONTROL
Each analogue output can be independently controlled. The headphone output control fields are
described in Table 43. The line output control fields are described in Table 44. The output pins are
described in more detail in “Analogue Outputs”.
The volume and mute status of each output can be controlled individually using the bit fields shown
in Table 43 and Table 44.
To prevent “zipper noise” when a volume adjustment is made, a zero-cross function is provided on all
output paths. When this function is enabled, volume updates will not take place until a zero-crossing
is detected. In the event of a long period without zero-crossings, a timeout will apply. The timeout
must be enabled by setting the TOCLK_ENA bit, as defined in “Clocking and Sample Rates”.
The volume update bits control the loading of the output driver volume data. For example, when
HPOUT_VU is set to 0, the headphone volume data can be loaded into the respective control
register, but will not actually change the gain setting. The Left and Right headphone volume settings
are updated when a 1 is written to HPOUT_VU. This makes it possible to update the gain of a
Left/Right pair of output paths simultaneously.
R61 (3Dh)
Analogue
OUT12 ZC
REGISTER
ADDRESS
BIT
3
2
1
0
LINEOUTR_BYP_
LINEOUTL_BYP_
HPR_BYP_ENA
HPL_BYP_ENA
LABEL
ENA
ENA
DEFAULT
0
0
0
0
Selects input for left headphone
output MUX
0 = Left DAC
1 = Left input PGA (Analogue
bypass)
Selects input for right headphone
output MUX
0 = Right DAC
1 = Right input PGA (Analogue
bypass)
Selects input for left line output
MUX
0 = Left DAC
1 = Left input PGA (Analogue
bypass)
Selects input for right line output
MUX
0 = Right DAC
1 = Right input PGA (Analogue
bypass)
PD, Rev 4.0, September 2010
DESCRIPTION
Production Data
68