STAC9750 Datasheet, PDF (58/73 Pages) Integrated Device Technology – VALUE-LINE TWO-CHANNEL AC’97 CODECS

STAC9750/9751
VALUE-LINE TWO-CHANNEL AC’97 CODECS
PC AUDIO
8. MULTIPLE CODEC SUPPORT
The STAC9750/9751 provides support for the multi-CODEC option according to the Intel AC'97, rev
2.2 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.
8.1. 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 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
74)”.
CID1 State
DVdd or floating
DVdd or floating
0V
0V
Table 41. CODEC ID Selection
CID0 State
DVdd or floating
0V
DVdd or floating
0V
CODEC ID
00
01
10
11
CODEC Status
Primary
Secondary
Secondary
Secondary
8.1.1.
Primary CODEC Operation
As a Primary device the STAC9750/9751 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 STAC9750/9751 operates 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 STAC9750/9751 generates the master AC-Link BIT_CLK
for both the AC'97 Digital Controller and any Secondary CODECs. The STAC9750/9751 can support
up to four loads of 10 KΩ and 50 pF on the BIT_CLK line. This is to ensure that implementations of
up to four CODECs will not load down the clock output.
8.1.2.
Secondary CODEC Operation
When the STAC9750/9751 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).
IDT™
VALUE-LINE TWO-CHANNEL AC’97 CODECS
58
STAC9750/9751
V 5.8 103106