WM8904 Datasheet, PDF (101/188 Pages) Wolfson Microelectronics plc – Ultra Low Power CODEC for Portable Audio Applications

Pre-Production
WM8904
LOOPBACK
Setting the LOOPBACK register bit enables digital loopback. When this bit is set, the ADC digital data
output is routed to the DAC digital data input path. The digital audio interface input (DACDAT) is not
used when LOOPBACK is enabled.
REGISTER BIT
ADDRESS
LABEL
R24 (18h)
8
LOOPBACK
Audio
Interface 0
Table 59 Loopback Control
DEFAULT
DESCRIPTION
0
Digital Loopback Function
0 = No loopback
1 = Loopback enabled (ADC data output
is directly input to DAC data input).
Note: When the digital sidetone is enabled, ADC data will also be added to DAC digital data input
path within the Digital Mixing circuit. This applies regardless of whether LOOPBACK is enabled.
DIGITAL PULL-UP AND PULL-DOWN
The WM8904 provides integrated pull-up and pull-down resistors on each of the MCLK, DACDAT,
LRCLK and BCLK pins. This provides a flexible capability for interfacing with other devices. Each of
the pull-up and pull-down resistors can be configured independently using the register bits described
in Table 60.
REGISTER BIT
ADDRESS
LABEL
DEFAULT
DESCRIPTION
R126 (7Eh)
Digital Pulls
7
MCLK_PU
0
MCLK pull-up resistor enable
0 = pull-up disabled
1 = pull-up enabled
6
MCLK_PD
0
MCLK pull-down resistor enable
0 = pull-down disabled
1 = pull-down enabled
5
DACDAT_PU
0
DACDAT pull-up resistor enable
0 = pull-up disabled
1 = pull-up enabled
4
DACDAT_PD
0
DACDAT pull-down resistor enable
0 = pull-down disabled
1 = pull-down enabled
3
LRCLK_PU
0
LRCLK pull-up resistor enable
0 = pull-up disabled
1 = pull-up enabled
2
LRCLK_PD
0
LRCLK pull-down resistor enable
0 = pull-down disabled
1 = pull-down enabled
1
BCLK_PU
0
BCLK pull-up resistor enable
0 = pull-up disabled
1 = pull-up enabled
0
BCLK_PD
0
BCLK pull-down resistor enable
0 = pull-down disabled
1 = pull-down enabled
Table 60 Digital Audio Interface Pull-Up and Pull-Down Control
w
PP, Rev 3.3, September 2012
101