Ac '97 Audio Codec Detect Circuit And Configuration Options; Figure 64. Cdc_Dn_Enab# Support Circuitry For A Single Codec On Motherboard - Intel 815EG Design Manual

I/O Subsystem
11.3.2 AC '97 Audio Codec Detect Circuit and Configuration
Options
The following provides general circuits to implement a number of different codec configurations.
For Intel recommended codec configurations, refer to the Intel
for ICHx/AC '97 Audio (Motherboard and Communication and Network Riser).
To support more than two channels of audio output, the ICH2 allows for a configuration where
two audio codecs work concurrently to provide surround capabilities. To maintain data-on-demand
capabilities, the ICH2 AC '97 controller, when configured for 4 or 6 channels, will wait for all the
appropriate slot request bits to be set before sending data in the SDATA_OUT slots. This allows
for simple FIFO synchronization of the attached codecs. It is assumed that both codecs will be
programmed to the same sample rate, and that the codecs have identical (or at least compatible)
FIFO depth requirements. It is recommended that the codecs be provided by the same vendor,
upon the certification of their interoperability in an audio channel configuration.
The following circuits (Figure 64, Figure 65, Figure 66, and Figure 67) show the adaptability of a
system with the modification of R
multiple codec configurations. This also provides a mechanism to make sure that only two codecs
are enabled in a given configuration and allows the configuration of the link to be determined by
the BIOS so that the correct PnP IDs can be loaded.

Figure 64. CDC_DN_ENAB# Support Circuitry for a Single Codec on Motherboard

From AC '97
Controller
To General
Purpose Input
To AC '97
Digital
Controller
As shown in Figure 64, when a single codec is located on the motherboard, the resistor R
circuitry (AND and NOT gates) shown inside the dashed box must be implemented, on the
motherboard. This circuitry is required to disable the motherboard codec when a CNR is installed
which contains two AC '97 codecs (or a single AC '97 codec which must be the primary codec on
the AC-Link).
112
and R combined with some basic glue logic to support
A B
Codec A
SDATA_IN
RESET#
AC97_RESET#
CDC_DN_ENAB#
R
10kohms
SDATA_IN0
SDATA_IN1
®
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Motherboard
A
®
Intel 815EG Chipset Platform Design Guide
CNR Board
Codec C
RESET#
SDATA_IN
Vcc
Codec D
R
RESET#
B
1kohms
SDATA_IN
CNR Connector
and the
A
R