STAC9708 Datasheet, PDF (36/56 Pages) List of Unclassifed Manufacturers – Multi-Channel AC97 Codec With Multi-Codec Option

SigmaTel, Inc.
Preliminary
STAC9708/11
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
+5V or floating
+5V or floating
0V
0V
CID0 STATE
+5V or floating
0V
+5V or floating
0V
CODEC ID
00
01
10
11
CODEC STATUS
Primary
Secondary
Secondary
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 KΩ 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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