WM9708

Advanced Information

WOLFSON MICROELECTRONICS LTD

AI Rev 2.0 April 2001

24

REGISTER 2Ah – EXTENDED AUDIO STATUS AND CONTROL REGISTER

The Extended Audio Status and Control Register is a read/write register that provides status and

control of the extended audio features.

DATA BIT

FUNCTION

READ/WRITE

WM9708 SUPPORT

VRA

Enables variable rate audio mode

Read/write

Yes

DRA

Enable double rate audio mode

Read/write

No

VRM

Enables variable rate Mic ADC

Read/write

No

CDAC

Indicates centre DAC ready

Read

No

SDAC

Indicates surround DAC ready

Read

No

LDAC

Indicates LFE DAC ready

Read

No

MADC

Indicates Mic ADC ready

Read

No

PRI

Set to turn off centre DAC

Read/write

No

PRJ

Set to turn off surround DACs

Read/write

No

PRK

Set to turn off LFE DACs

Read/write

No

PRL

Set to turn off Mic ADC

Read/write

No

Table 13 Extended Audio Status and Control Register

REGISTER 2Ch TO 32h – AUDIO SAMPLE RATE CONTROL REGISTERS

These registers are read/write registers that are written to, to select alternative sample rates for the

audio PCM converters. Default is the 48ks/s rate. Note that only Revision 2.1 recommended rates

are supported by the WM9708, selection of any other unsupported rates will cause the rate to default

to the nearest supported rate, and the supported rate value to be latched and so read back.

REGISTERS 36h AND 38h – 6 CHANNEL VOLUME CONTROL

These read/write registers control the output volume of the optional four PCM channels. (not

supported by the WM9708)

VENDOR RESERVED REGISTERS (INDEX 5Ah - 7Ah)

These registers are vendor specific. Do not write to these registers unless the Vendor ID register has

been checked first to ensure that the driver knows the source of the AC ‘97 component.

VENDOR SPECIFIC REGISTER (INDEX 5Ch)

The WM9708 can be programmed to automute the DACs. By setting the mute bit, the WM9708 will

mute the DACs when it detects a continuous sequence of 1024 zeros.

VENDOR SPECIFIC GAIN CONTROL REGISTERS – (INDEX 72h)

This register controls the gain and mute functions applied to the mixer path. This PGA is not

accommodated in the Intel specification, but is required in order to allow the option of simultaneous

recording of the mixer output and playback of DAC signals. The function is as per the other mixer

PGA’s. However, the default value of the register is not-muted. If it is not used it will be transparent to

the user.

VENDOR ID REGISTERS (INDEX 7Ch TO 7Eh)

This register is for specific vendor identification if so desired. The ID method is Microsoft’s Plug and

Play Vendor ID code. The first character of that ID is F7 to F0, the second character S7 to S0, and

the third T7 to T0. These three characters are ASCII encoded. The REV7 to REV0 field is for the

Vendor Revision number. In the WM9708 the vendor ID is set to WML3.

Wolfson is a registered Microsoft Plug and Play vendor.

VENDOR ID REGISTERS (INDEX 74h)

This register describes how data is mapped to the AC’97 DACs. Register 74h can be used to change

the incoming DAC data slots that are used by the on-board DACs. This allows software control of

multiple codecs. If used it is recommended that the ID is configured before any other registers and

before the data is applied to the system.