STAC9708 datasheet(20/56 Pages) ETC

20 / 56 page

SigmaTel, Inc.

Preliminary

STAC9708/11

10/02/98

A new audio input frame begins with a low to high transition of SYNC. SYNC is synchronous to the

rising edge of BIT_CLK. On the immediately following falling edge of BIT_CLK, STAC9708/11

samples the assertion of SYNC. This falling edge marks the time when both sides of AC-Link are

aware of the start of a new audio frame. On the next rising of BIT_CLK, the STAC9708/11 transitions

SDATA_IN into the first bit position of slot 0 ("Codec Ready" bit). Each new bit position is presented

to AC-Link on a rising edge of BIT_CLK and subsequently sampled by the AC'97 controller on the

following falling edge of BIT_CLK.

This sequence ensures that data transitions, and subsequent

sample points for both incoming and outgoing data streams are time aligned.

Figure 9. Start of an Audio Input Frame

SYNC

BIT_CLK

SDATA_IN

STAC9708 samples first SDATA_OUT bit of frame here

STAC9708 samples SYNC assertion here

Codec

Ready

slot1

slot2

End of previous audio frame

SDATA_IN's composite stream is MSB justified (MSB first) with all non-valid bit positions (for

assigned and/or unassigned time slots) stuffed with 0's by STAC9708/11. SDATA_IN data is sampled

on the falling edges of BIT_CLK.

3.1.2.1 Slot 1: Status Address Port

The status port is used to monitor status for STAC9708/11 functions including, but not

limited to, mixer settings, and power management.

Audio input frame slot 1’s stream echoes the control register index, for historical reference,

for the data to be returned in slot 2. (Assuming that slots 1 and 2 had been tagged “valid” by

STAC9708/11 during slot 0)

Status Address Port hit assignments:

Bit (19)

RESERVED

(Stuffed with 0)

Bit (18;12) Control Register Index

(Echo of register index for which data is being returned)

Bit (11:0)

RESERVED

(Stuffed with 0's)

The first bit (MSB) generated by STAC9708/11 is always stuffed with a 0. The following 7

bit positions communicate the associated control register address, and the trailing 12 bit

positions are stuffed with 0's by STAC9708/11.

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