STAC9766 datasheet(36/97 Pages) IDT

36 / 97 page

STAC9766/9767

TWO-CHANNEL, 20-BIT, AC’97 2.3 CODECS WITH STEREO MICROPHONE AND MIC/JACK SENSING

PC AUDIO

IDT™

STAC9766/9767

V 7.4 12/06

TWO-CHANNEL, 20-BIT, AC’97 2.3 CODECS WITH STEREO MICROPHONE AND MIC/JACK SENSING

and 2 had been tagged “valid” by the AC‘97 CODEC during slot 0.

The first bit (MSB) generated by AC‘97 is always stuffed with a 0. The following 7 bit positions com-

municate the associated control register address, the next 10 bits support AC‘97’s variable sample

rate signaling protocol, and the trailing 2 bit positions are stuffed with 0 by AC‘97.

5.4.2.2.

SLOTREQ signaling bits

AC-link input frame Slot 1, the Status Address Port, now delivers CODEC control register read

address and variable sample rate slot request flags for all output slots. Ten of the formerly reserved

least significant bits have been defined as data request flags for output slots 3-12.

The AC-link input frame Slot 1 tag bit is independent of the bit 11-2 slot request field, and ONLY indi-

cates valid Status Address Port data (Control Register Index). The CODEC should only set

SDATA_IN tag bits for Slot 1 (Address) and Slot 2 (Data) to 1 when returning valid data from a previ-

ous register read. They should otherwise be set to 0. SLOTREQ bits have validity independent of the

Slot 1 tag bit.

SLOTREQ bits are always 0 in the following cases

•

Fixed rate mode (VRA = 0)

•

Inactive (powered down) ADC channel

SLOTREQ bits are only set to 1 by the CODEC in the following case

•

Variable rate audio mode (VRA = 1) AND active (power ready) ADC AND a non-48 KHz ADC

sample rate and CODEC does not need a sample

5.4.3.

Slot 2: Status Data Port

The status data port delivers 16-bit control register read data.

If Slot 2 is tagged invalid by AC‘97, then the entire slot will be stuffed with 0 by AC‘97.

Table 9. Status Address Port Bit Assignments

Bit

Description

Comments

Reserved

Stuffed with 0

18:12

Control Register Index

Echo of register index for which data is being returned

11:2

SLOTREQ

See Next Section

1:0

Reserved

Stuffed with 0

Table 10. Status Data Port Bit Assignments

Bit

Description

Comments

19:4

Control Register Read Data

Stuffed with 0 if tagged “invalid”

3:0

Reserved

Stuffed with 0

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