Figure 65. Cdc_Dn_Enab# Support Circuitry For Multi-Channel Audio Upgrade - Intel 815EG Design Manual

R
By installing resistor R
(held in reset) and the codec(s) on the CNR take control of the AC-Link. One possible example of
using this architecture is a system integrator installing an audio plus modem CNR in a system
already containing an audio codec on the motherboard. The audio codec on the motherboard
would then be disabled, allowing all of the codecs on the CNR to be used.
The architecture shown in Figure 65 has some unique features. These include the possibility of the
CNR being used as an upgrade to the existing audio features of the motherboard (by simply
changing the value of resistor R
increasing from two-channel to four or six-channel audio.
Both Figure 65 and Figure 66 show a switch on the CNR board. This is necessary to connect the
CNR board codec to the proper SDATA_INn line as to not conflict with the motherboard
codec(s).

Figure 65. CDC_DN_ENAB# Support Circuitry for Multi-Channel Audio Upgrade

Figure 66 shows the circuitry required on the motherboard to support a two-codec down
configuration. This circuitry disables the codec on a single codec CNR. Notice that in this
configuration the resistor, R
®
Intel 815EG Chipset Platform Design Guide
(1 kΩ) on the CNR, the codec on the motherboard becomes disabled
B
on the CNR to 100 kΩ). An example of one such upgrade is
B
From AC '97 AC97_RESET#
Controller
To General CDC_DN_ENAB#
Purpose Input
SDATA_IN0
To AC '97
Digital
SDATA_IN1
Controller
, has been changed to 100 kΩ.
B
Motherboard
Primary
Audio
Codec
SDATA_IN
RESET#
R
A
10kohms
I/O Subsystem
CNR Board
Audio
Codec
RESET#
SDATA_IN
ID0#
Vcc
R
B
100kohms
CNR Connector
113