Figure 100. Cdc_Dn_Enab# Support Circuitry For A Single Codec Motherboard - Intel Pentium 4 Design Manual

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Figure 100. CDC_DN_ENAB# Support Circuitry for a Single Codec Motherboard

From AC '97
Controller
T o G eneral
Purpose
To AC '97
Controller
As shown in Figure 100 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 in order 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).
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 101 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 101 and Figure 102 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).
® ®
Intel Pentium 4 Processor / Intel
Codec A
SDAT A_IN
RESET #
AC97_RESET#
CDC_DN_ENAB#
Input
SDATA_IN0
Digital
SDATA_IN1
(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
®
850 Chipset Family Platform Design Guide
M otherboard CNR Board
Vcc
R
A
10K Ω
I/O Controller Hub 2
Codec C
RESET#
SDAT A_IN
Codec D
R
RESET#
B
1K Ω
SDATA_IN
CNR Connector
CNR_MotherB_Single-Codec
and the
A
145