Intel 820E Benutzerhandbuch

Design Guide 

 

87 

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As shown in Figure 51, 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 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

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. 

The architecture shown in  Figure 52 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 52 and Figure 53 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).