Specifications

Intel
®
810E2 Chipset Platform
R
Design Guide 65
As shown in the following figure, when a single codec is located on the motherboard, the resistor R
A
and
the 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
containing two AC ’97 codecs (or a single AC ’97 codec that must be the primary codec on the
AC-Link).
By installing resistor R
B
(1 kΩ) on the CNR, the codec on the motherboard becomes disabled (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.
Figure 33. CDC_DN_ENAB# Support Circuitry for a Single Codec on Motherboard
AC97_1
Codec A
RESET#
SDATA_IN
Codec C
RESET#
SDATA_IN
AC97_RESET#
Vcc
CDC_DN_ENAB#
CNR BoardMotherboard
R
A
10kohms
R
B
1kohms
To General
Purpose Input
From AC '97
Controller
CNR Connector
To AC '97
Digital
Controller
SDATA_IN0
SDATA_IN1
Codec D
RESET#
SDATA_IN
The architecture shown in Figure 34 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
B
on the CNR to 100 kΩ). An example of one such upgrade is increasing from two-channel
to four or six-channel audio.
Both Figure 34 and Figure 35 show a switch on the CNR board. This is necessary to connect the CNR
board codec to the proper SDATA_INn line so there is not a conflict with the motherboard codec(s).