STAC9766 IDT [Integrated Device Technology], STAC9766 Datasheet - Page 83

• Manufacturer Part Number: STAC9766
• Manufacturer: IDT [Integrated Device Technology]

10.MULTIPLE CODEC SUPPORT
IDT™
TWO-CHANNEL, 20-BIT, AC’97 2.3 CODECS WITH STEREO MICROPHONE AND MIC/JACK SENSING
STAC9766/9767
TWO-CHANNEL, 20-BIT, AC’97 2.3 CODECS WITH STEREO MICROPHONE AND MIC/JACK SENSING
10.1. Primary/Secondary CODEC Selection
10.1.1.
10.1.2.
The STAC9766/9767 provides support for the multi-CODEC option according to the Intel AC'97, rev
2.3 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 accessi-
ble and they do not share registers.
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 desig-
nation. 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 74h)”.
Primary CODEC Operation
As a Primary device the STAC9766/9767 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 STAC9766/9767operates as Primary by default, and the
external ID pins (45 and 46), have internal pull-ups so that these pins may be left as no-connects for
primary operation.
When used as the Primary CODEC, the STAC9766/9767 generates the master AC-Link BIT_CLK
for both the AC'97 Digital Controller and any Secondary CODECs. The STAC9766/9767can support
up to four loads of 10 K / 50 pF on the BIT_CLK output. This is to ensure that up to four CODECs
will not load down the clock output.
Secondary CODEC Operation
When the STAC9766/9767 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).
Dvdd or floating
Dvdd or floating
CID1 State
0V
0V
Dvdd or floating
Dvdd or floating
CID0 State
Table 30. CODEC ID Selection
0V
0V
83
CODEC ID
00
01
10
11
STAC9766/9767
CODEC Status
Secondary
Secondary
Secondary
Primary
PC AUDIO
V 7.4 12/06