Intel 820E manual Signal Descriptions, Cdcdnenab#, AC97RESET#

Intel® 820E Chipset

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Figure 54. CDC_DN_ENAB# Support Circuitry for Two-Codecs on Motherboard / Two-Codecs on

CNR

	Codec A	Codec B	Motherboard	CNR Board
	SDATA_IN	SDATA_IN
	RESET#	RESET#
						Codec C
						RESET#
From AC '97	AC97_RESET#					SDATA_IN
Controller
				Vcc		Codec D
				RB
To General	CDC_DN_ENAB#					RESET#
				1	κΩ	SDATA_IN
Purpose Input	RA
	10 kΩ
To AC '97	SDATA_IN0
Digital	SDATA_IN1
Controller
				CNR Connector

Circuit Notes

1.While it is possible to disable down codecs, as shown above in Figure 53 and Figure 54, it is recommended against for reasons cited in the ICHx/AC'97 White Paper, including avoidance of shipping redundant and/or non-functional audio jacks.

2.All CNR designs include resistor RB. The value of RB is either 1 kΩ or 100 kΩ, depending on the intended functionality of the CNR (whether or not it intends to be the primary/controlling codec).

3.Any CNR with two codecs must implement RB with value 1 kΩ. If there is one codec, use a

100 kΩ pull-up resistor. A CNR with zero codecs must not stuff RB. If implemented, RB must be connected to the same power well as the codec so that it is valid whenever the codec has power.

4.A motherboard with one or more codecs down must implement RA with a value of 10 kΩ.

5.The CDC_DN_ENAB# signal must be run to a GPI so that the BIOS can sense the state of the signal. CDC_DN_ENAB# is required to be connected to a GPI; a connection to a GPIO is strongly recommended for testing purposes.

Table 18. Signal Descriptions

CDC_DN_ENAB#	When low, indicates that the codec on the motherboard is enabled and
	primary on the AC’97 Interface. When high, indicates that the motherboard
	codec(s) must be removed from the AC’97 Interface (held in reset), because
	the CNR codec(s) will be the primary device(s) on the AC’97 Interface.
AC97_RESET#	Reset signal from the AC’97 Digital Controller (ICH2).
SDATA_INn	AC’97 serial data from an AC’97-compliant codec to an AC’97-compliant
	controller (i.e., the ICH2).

Design Guide 89