STAC9721 datasheet(13/48 Pages) ETC1

13 / 48 page

SigmaTel, Inc.

Data Sheet

STAC9721

04/07/00

Figure 6. Start of an Audio Output Frame

SYNC

BIT_CLK

SDATA_OUT

first SDATA_OUT bit of frame here

SYNC assertion here

valid

Frame

slot1

slot2

End of previous audio frame

SDATA_OUT’s composite stream is MSB justified (MSB first) with all non-valid slots’

bit positions stuffed with 0’s by the AC'97 controller.

When mono audio sample streams are sent from the AC'97 controller it is necessary that

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

3.1.1.1

Slot 1: Command Address Port

The command port is used to control features, and monitor status (see Audio Input Frame

Slots 1 and 2) of the STAC9721/23 functions including, but not limited to, mixer

settings, and power management (refer to the control register section of this

specification).

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.

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

command information to the STAC9721/23.

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 0's)

The first bit (MSB) sampled by STAC9721/23 indicates whether the current control

transaction is a read or a 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 he stuffed with 0's by the AC'97 controller.

3.1.1.2

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 0's if current operation is a

read)

Bit (3 :0)

Reserved

(Stuffed with 0's)

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