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Design Guide 23
1.4.9. AC’97
The Audio Codec ’97 (AC’97) specification defines a digital interface that can be used to attach an audio
codec (AC), a modem codec (MC), an audio/modem codec (AMC) or both an AC and an MC. The
AC’97 specification defines the interface between the system logic and the audio or modem codec,
known as the AC’97 Digital Link.
The Intel 820E chipset platform’s AC’97 (with the appropriate codecs) not only replaces ISA audio and
modem functionality, but also improves overall platform integration by incorporating the AC’97 digital
link. The use of the ICH2-integrated AC’97 digital link reduces cost and eases migration from ISA.
By using an audio codec, the AC’97 digital link allows for cost-effective, high-quality, integrated audio
on an Intel 820E chipset-based platform. In addition, an AC’97 soft modem can be implemented with the
use of a modem codec. Several system options exist when implementing AC’97. The ICH2-integrated
digital link allows several external codecs to be connected to the ICH2. The system designer can provide
audio with an audio codec, a modem with a modem codec, or an integrated audio/modem codec (Figure
4C). The digital link is expanded to support two audio codecs or a combination of an audio and modem
codec (Figures 4A and 4B).
The modem implementations for different countries must be taken into consideration, because telephone
systems may vary. By using a split design, the audio codec can be on-board and the modem codec can be
placed on a riser. Intel is developing an AC’97 digital link connector. With a single integrated codec, or
AMC, both audio and modem can be routed to a connector near the rear panel, where the external ports
can be located.
The digital link in the ICH2 is compliant with Revision 2.1 of the AC’97 specification, so it supports two
codecs with independent PCI functions for audio and modem. Microphone input and left and right audio
channels are supported for a high quality, two-speaker audio solution. Wake on Ring from Suspend also
is supported with the appropriate modem codec.
The ICH2 expands the audio capability with support for up to six channels of PCM audio output (full
AC3 decode). Six-channel audio consists of Front Left, Front Right, Back Left, Back Right, Center, and
Woofer, for a complete surround-sound effect. ICH2 has expanded support for two audio codecs on the
AC’97 digital link.