Production Data

WM9703

WOLFSON MICROELECTRONICS LTD

PD Rev 3.4 January 2001

15

CONTROL INTERFACE

A digital interface has been provided to control the WM9703 and transfer data to and from it. This

serial interface is compatible with the Intel AC’97.

The main control interface functions are:

•

Control of analogue gain and signal paths through the mixer

•

Bi-directional transfer of ADC and DAC words to and from AC’97 controller

•

Selection of powerdown modes

AC-LINK DIGITAL SERIAL INTERFACE PROTOCOL

The WM9703 incorporates a 5-pin digital serial interface that links it to the AC’97 controller. AC-link

is a bi-directional, fixed rate, serial PCM digital stream. It handles multiple input and output audio

streams, as well as control register accesses employing a time division multiplexed (TDM) scheme.

The AC-link architecture divides each audio frame into 12 outgoing and 12 incoming data streams,

each with 20-bit sample resolution. With a minimum required DAC and ADC resolution of 16-bits,

AC’97 may also be implemented with 18 or 20-bit DAC/ADC resolution, given the headroom that the

AC-link architecture provides. The WM9703 provides support for 18-bit operation.

SLOT

NUMBER

SYNC

SDATA_OUT

SDATA_IN

TAG PHASE

TAG

CMD

ADR

CMD

DATA

PCM

LEFT

PCM

RIGHT

RSRVD

PCM

LFE

RSRVD

RSRVD

TAG

STATUS

ADDR

STATUS

DATA

PCM

LEFT

PCM

RIGHT

RSRVD

RSRVD

RSRVD

RSRVD

RSRVD

RSRVD

RSRVD

RSRVD

DATA PHASE

0

1

2345

6789

10

11

12

PCM

CENTRE

PCM

L SURR

PCM

R SURR

RSRVD

PCM C

(n+1)

PCM R

(n+1)

PCM L

(n+1)

CODEC ID

SLOTREQ 3-12

Figure 12 AC’97 Standard Bi-directional Audio Frame

SYNC

BIT_CLK

SDATA_OUT

VALID

FRAME

SLOT(1)

SLOT(2)

SLOT(12)

’0’

(ID1)

(ID0)

19

0

19

0

19

0

19

0

TAG PHASE

DATA PHASE

20.8

µS (48kHz)

12.288MHz

81.4nS

END OF PREVIOUS

AUDIO FRAME

TIME SLOT ’VALID’ BITS

(’1’ = TIME SLOT CONTAINS

VALID PCM DATA)

SLOT (1)

SLOT (2)

SLOT (3)

SLOT (12)

Figure 13 AC-link Audio Output Frame