STAC9704 datasheet(15/49 Pages) HYNIX

15 / 49 page

SigmaTel, Inc.

STAC9704/7

10/02/98

Figure 7: Start of an Audio Output Frame

SYNC

BIT_CLK

SDATA_OUT

STAC9701 samples first SDATA_OUT bit of frame here

STAC9701 samples 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 STAC9704/7 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 STAC9704/7.

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 STAC9704/7 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.

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