Advanced Information

WM9708

WOLFSON MICROELECTRONICS LTD

AI Rev 2.0 April 2001

19

WARM WM9708 RESET

A warm WM9708 reset will re-activate the AC-link without altering the current WM9708 register

values. A warm reset is signalled by driving SYNC high for a minimum of 1

µs in the absence of

BITCLK. See Figure 3.

Within normal audio frames SYNC is a synchronous input. In the absence of BITCLK, SYNC is

treated as an asynchronous input used in the generation of a warm reset to the WM9708.

The

WM9708 will not respond with the activation of BITCLK until SYNC has been sampled low again by

the WM9708. This will preclude the false detection of a new audio frame.

SERIAL INTERFACE REGISTER MAP DESCRIPTION

(See Table 15)

The serial interface bits perform control functions described as follows: The register map is fully

specified by the AC’97 specification, and this description is simply repeated below, with optional

unsupported features omitted.

RESET REGISTER (INDEX 00h)

Writing any value to this register performs a register reset, which causes registers 0-2B inclusive to

revert to their default values. Reading this register returns the ID code of the part, indication of

modem support (not supported by the WM9708) and a code for the type of 3D stereo enhancement

(not supported by the WM9708).

The ID decodes the capabilities of the WM9708 based on the following:

BIT

FUNCTION

VALUE ON

WM9708

ID0

Dedicated Mic PCM in channel

0

ID1

Modem line codec support

0

ID2

Bass and treble control

0

ID3

Simulated stereo (mono to stereo)

0

ID4

Headphone out support

1

ID5

Loudness (bass boost) support

0

ID6

18-bit DAC resolution

1

ID7

20-bit DAC resolution

0

ID8

18-bit ADC resolution

1

ID9

20-bit ADC resolution

0

SE4...SE0

No 3D support

00000

Table 3 Reset Register Function

Note that the WM9708 defaults to indicate 18-bit compatibility.

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 to ML0 is for left channel level, MR5 to MR0 is for the right channel and MM5 to MM0 is for the

mono out channel.

Support for the MSB of the volume level is not provided by the WM9708. If the MSB is written to,

then the WM9708 detects when that bit is set and sets all 4 LSBs to 1s. Example: If the driver writes

a 1xxxxx the WM9708 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.