Production Data

WM9704M

WOLFSON MICROELECTRONICS LTD

PD Rev 3.2 January 2001

25

Note that the WM9704M defaults to indicate 18-bit compatibility. However, a control bit may be set in

the vendor-specific registers that changes bits ID6 and ID8 to be ‘0’, indicating a 16-bit device. It is

unlikely that this function will be required, however, as the MSB justification of the ADC and DAC

data means that a nominally 18-bit device should be fully compatible with controllers that only

provide 16-bit support. Most PC type applications will only require 16-bit operation.

PLAY MASTER VOLUME REGISTERS (INDEX 02H, 04H AND 06H)

These registers manage the output signal volumes. Register 02h controls the stereo master volume

(both right and left channels), Register 04h controls the optional stereo headphone out, and Register

06h controls the mono volume output. Each step corresponds to 1.5dB. The MSB of the register is

the mute bit. When this bit is set to 1 the level for that channel is set at -

ML5 through ML0 is for left channel level, ML5 through ML0 is for the right channel and MM5 through

MM0 is for the mono out channel.

Support for the MSB of the volume level is not provided by the WM9704M. If the MSB is written to,

then the WM9704M detects when that bit is set and sets all 4 LSBs to 1s. Example: If the driver

writes a 1xxxxx the WM9704M interprets that as x11111. It will also respond when read with x11111

rather than 1xxxxx, the value written to it. The driver can use this feature to detect if support for the

6th bit is there or not.

The default value of both the mono and the stereo registers is 8000h (1000 0000 0000 0000), which

corresponds to 0dB gain with mute on.

MUTE

MX4...MX0

FUNCTION

0

0 0000

0dB attenuation

0

0 0001

1.5dB attenuation

0

1 1111

46.5dB attenuation

1

x xxxx

Table 10 Volume Register Function

MASTER TONE CONTROL REGISTERS (INDEX 08H)

Optional register for support of tone controls (bass and treble). The WM9704M does not support

bass and treble and writing to this register will have no effect, reading will result in all don’t care

values.

PC BEEP REGISTER (INDEX 0AH)

This controls the level for the PC-beep input. Each step corresponds to approximately 3dB of

attenuation. The MSB of the register is the mute bit. When this bit is set to 1 the level for that

channel is set at -

WM9704M defaults to the PC-beep path being muted, except during reset when the path is open, so

an external speaker should be provided within the PC to alert the user to power on self-test

problems.

MUTE

PV3...PV0

FUNCTION

0

0000

0dB attenuation

0

1111

45dB attenuation

1

xxxx

Table 11 PC-beep Register Function

ANALOGUE MIXER INPUT GAIN REGISTERS (INDEX 0CH - 18H)

This controls the gain/attenuation for each of the analogue inputs. Each step corresponds to

approximately 1.5dB. The MSB of the register is the mute bit. When this bit is set to 1 the level for

that channel is set at -

REGISTER 0EH (MIC VOLUME REGISTER)

This has an extra bit that is for a 20dB boost. When bit 6 is set to 1 the 20dB boost is on. The default

value is 8008, which corresponds to 0dB gain with mute on.

The default value for the mono registers is 8008h, which corresponds to 0dB gain with mute on. The

default value for stereo registers is 8808h, which corresponds to 0dB gain with mute on.