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Intel
®
820E Chipset
R
Design Guide 85
2.13. AC’97
The ICH2 implements an AC’97 2.1-compliant digital controller. Any codec attached to the ICH2
AC-link also must be AC’97 2.1 compliant. Please contact your codec IHV for information on
2.1-compliant products. The AC’97 2.1 specification is on the following Intel web page:
http://developer.intel.com/pc-supp/platform/ac97/index.htm
The AC-link is a bi-directional, serial PCM digital stream. It handles multiple input and output data
streams as well as control register accesses, employing a time division multiplexed (TDM) scheme. The
AC-link architecture provides for data transfer through individual frames transmitted serially. Each frame
is divided into 12 outgoing and 12 incoming data streams, or slots. The architecture of the ICH2 AC-link
allows a maximum of two codecs to be connected. The following figure shows a two-codec topology of
the AC-link for the ICH2.
Figure 50. ICH2 AC’97– Codec Connection
AC '97 2.1
controller section
of ICH2
Digital AC '97
2.1 controller
Primary codec
Secondary codec
AC / MC
AC / MC / AMC
ICH2_AC97_codec_conn
SDIN 0
SDIN 1
RESET#
SDOUT
SYNC
BIT_CLK
The AC’97 interface can be routed using 5 mil traces, with 5 mil space between traces. The maximum
length from ICH2 to CODEC/CNR is 14 inches, in a tee topology. This assumes that a CNR riser card
implements its audio solution with a maximum trace length of 4 inches for the AC-link. The trace
impedance should be as follows: Z
0
= 60 Ω ± 15%.