STAC9708 datasheet(36/56 Pages) ETC

36 / 56 page

SigmaTel, Inc.

Preliminary

STAC9708/11

10/02/98

6. MULTIPLE CODEC SUPPORT

The STAC9708/11 provides support for the multi-codec option according to the Intel AC'97, rev 2.1 specification.

By definition there can be only one Primary Codec (Codec ID 00) and up to three Secondary Codecs (Codec IDs

01,10, and 11).

The Codec ID functions as a chip select.

Secondary devices therefore have completely

orthogonal register sets; each is individually accessible and they do not share registers.

6.1

Primary/Secondary Codec Selection

In a multi-codec environment the codec ID is provided by external programming of pins 45 and 46 (CID0 and

CID1). The CID pin electrical function is logically inverted from the codec ID designation. The corresponding

pin state and its associated codec ID are listed in the "Codec ID Selection" table. Also see slot assignment

discussion, “Multi-Channel Programming Register (Index 74)”.

Table 21. Codec ID Selection

CID1 STATE

CID0 STATE

CODEC ID

CODEC STATUS

+5V or floating

Primary

+5V or floating

Secondary

+5V or floating

Secondary

6.1.1

Primary Codec Operation

As a Primary device the STAC9708/11 is completely compatible with existing AC'97 definitions and

extensions. Primary Codec registers are accessed exactly as defined in the AC'97 Component Specification

and AC'97 Extensions. The STAC9708/11 operates as Primary by default, and the external ID pins (47 and

48), have internal pull-ups so that these pins may be left as no-connects for primary operation.

When used as the Primary Codec, the STAC9708/11 generates the master AC-Link BIT_CLK for both the

AC'97 Digital Controller and any Secondary Codecs. The STAC9708/11 can support up to 4, 10 K

Ω 50 pF

loads on the BIT_CLK. This is to insure that up to 4 Codec implementations will not load down the clock

output.

6.1.2 Secondary Codec Operation

When the STAC9708/11 is configured as a Secondary device the BIT_CLK pin is configured as an input at

power up. Using the BIT_CLK provided by the Primary Codec insures that everything on the AC-Link will

be synchronous. As a Secondary device it can be defined as Codec ID 01, 10, or 11 in the two-bit field(s) of

the Extended Audio and/or Extended Modem ID Register(s).

6.2

Secondary Codec Register Access Definitions

The AC'97 Digital Controller can independently access Primary and Secondary Codec registers by using a 2-bit

Codec ID field (chip select) which is defined as the LSBs of Output Slot 0. For Secondary Codec access, the

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