Advanced Information

WM9707

WOLFSON MICROELECTRONICS LTD

AI Rev 2.2 January 2001

19

SLOT 4: PCM RECORD RIGHT CHANNEL

Audio input frame slot 4 is the right channel output of the WM9707’s input Mux, post-ADC.

The WM9707’s ADCs can be implemented to support 16, 18, or 20-bit resolution.

The WM9707 ships out its ADC output data (MSB first), and stuffs any trailing non-valid bit positions

with 0s to fill out its 20-bit time slot.

SLOT 5: OPTIONAL MODEM LINE CODEC

Not supported by WM9707.

SLOT 6: OPTIONAL DEDICATED MICROPHONE RECORD DATA

Not supported by WM9707.

SLOTS 7 TO 12: RESERVED

Audio input frame slots 7 to 12 are reserved for future use and are always stuffed with 0s by the

WM9707.

AC-LINK LOW POWER MODE

The AC-link signals can be placed in a low power mode. When the WM9707’s Powerdown Register

26h, is programmed to the appropriate value, both BIT_CLK and SDATA_IN will be brought to, and

held at a logic low voltage level.

BIT_CLK and SDATA_IN are transitioned low immediately following the decode of the write to the

Powerdown Register 26h with PR4. When the AC’97 controller driver is at the point where it is ready

to program the AC-link into its low power mode, slots 1 and 2 are assumed to be the only valid

stream in the audio output frame. At this point in time it is assumed that all sources of audio input

have also been neutralised.

The AC’97 controller should also drive SYNC and SDATA_OUT low after programming the WM9707

to this low power, halted mode.

Once the WM9707 has been instructed to halt BIT_CLK, a special wake up protocol must be used to

bring the AC-link to the active mode since normal audio output and input frames can not be

communicated in the absence of BIT_CLK.

WAKING UP THE AC-LINK

There are 2 methods for bringing the AC-link out of a low power, halted mode. Regardless of the

method, it is the AC’97 controller that performs the wake up task.

AC-link protocol provides for a Cold WM9707 Reset, and a Warm WM9707 Reset.

The current Powerdown state would ultimately dictate which form of WM9707 reset is appropriate.

Unless a cold or register reset (a write to the Reset Register 00h) is performed, wherein the WM9707

registers are initialised to their default values, registers are required to keep state during all

Powerdown modes.

Once powered down, re-activation of the AC-link via re-assertion of the SYNC signal must not occur

for a minimum of 4 audio frame times following the frame in which the Powerdown was triggered.

When AC-link powers up it indicates readiness via the Codec Ready bit (input slot 0, bit 15).

COLD WM9707 RESET

A cold reset is achieved by asserting RESETB for the minimum specified time (1

µs). By driving

RESETB low, BIT_CLK, and SDATA_OUT will be activated, or re-activated as the case may be, and

all the WM9707 control registers will be initialised to their default power on reset values.

RESETB is an asynchronous WM9707 input.