WM9704Q

Production Data

WOLFSON MICROELECTRONICS LTD

PD Rev 2.3 January 2001

20

As an example, consider an 8-bit sample stream that is being played out to one of the WM9704Q’s

DACs. The first 8 bit positions are presented to the DAC (MSB justified) followed by the next 12 bit

positions, which are stuffed with 0s by the AC’97 controller. This ensures that regardless of the

resolution of the implemented DAC (16, 18 or 20-bit), no DC biasing will be introduced by the least

significant bits. When mono audio sample streams are output from the AC’97 controller, it is

necessary that BOTH left and right sample stream time slots be filled with the same data.

SLOT 1: COMMAND ADDRESS PORT

The command port is used to control features and monitor status for the WM9704Q functions

including, but not limited to, mixer settings, and power management (refer to the register section).

The control interface architecture supports up to 64, 16-bit read/write registers, addressable on even

byte boundaries. Only the even registers (00h, 02h, etc.) are valid, odd register (01h, 03h, etc.)

accesses are discouraged (if supported they should default to the preceding even byte boundary -

i.e. a read to 01h will return the 16-bit contents of 00h). The WM9704Q’s control register file is

nonetheless readable as well as writeable to provide more robust testability.

Audio output frame slot 1 communicates control register address, and read/write command

information to the WM9704Q.

COMMAND ADDRESS PORT BIT ASSIGNMENTS

Bit (19)

Read/write command (1 = read, 0 = write)

Bit (18:12)

Control register index (64 16-bit locations, addressed on even

byte boundaries)

Bit (11:0)

Reserved (stuffed with 0s)

The first bit (MSB) sampled by the WM9704Q indicates whether the current control transaction is a

read or write operation. The following 7 bit positions communicate the targeted control register

address. The trailing 12 bit positions within the slot are reserved and must be stuffed with 0s by the

AC’97 controller.

SLOT 2: COMMAND DATA PORT

The command data port is used to deliver 16-bit control register write data in the event that the

current command port operation is a write cycle. (As indicated by slot 1, bit 19).

Bit (19:4)

Control register write data (stuffed with 0s if current operation is

a read)

Bit (3:0)

Reserved (stuffed with 0s)

If the current command port operation is a read then the entire time slot must be stuffed with 0s by

the AC’97 controller.

SLOT 3: PCM PLAYBACK LEFT CHANNEL

Audio output frame slot 3 is the composite digital audio left playback stream. In a typical Games

Compatible PC this slot is composed of standard PCM (.wav) output samples digitally mixed (on the

AC’97 controller or host processor) with music synthesis output samples. If a sample stream of

resolution less than 20-bits is transferred, the AC’97 controller must stuff all trailing non-valid bit

positions within this time slot with 0s.

SLOT 4: PCM PLAYBACK RIGHT CHANNEL

Audio output frame slot 4 is the composite digital audio right playback stream. In a typical Games

Compatible PC this slot is composed of standard PCM (.wav) output samples digitally mixed (on the

AC’97 controller or host processor) with music synthesis output samples.

If a sample stream of resolution less than 20-bits is transferred, the AC’97 controller must stuff all

trailing non-valid bit positions within this time slot with 0s.

SLOT 5: OPTIONAL MODEM LINE 1 CODEC

Slot 5 is not supported.

SLOTS 6 TO 9: SURROUND SOUND DATA

Audio output frame slots 6 to 9 are used to send surround sound data to the extra DAC channels.

These slots are supported by WM9704Q in Revision 2.1 6-channel mode and Quad mode. Note that

the data in the surround sound slots may be applied to either the internal DACs, or sent out onto the

GPIO pins as I