Intel 820E manual System Management, Rtc, AC’97

Intel® 820E Chipset

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Table 36. System Management

Checklist Items	Recommendations	Reason/Effect
SMBDATA	Requires external pull-up resistors to 3.3 V	Value of pull-up resistors is determined
SMBCLK	or 3.3 V standby.	by the line load. Open-drain signal in
		resume well
SMBALERT#/	See GPIO section if SMBALERT# not
GPIO[11]	implemented.
SMLINK[1:0]	Requires external pull-up resistors to 3.3 V.	Open-drain signal in resume well
INTRUDER#	Pull signal to VBAT if not needed.	Signal in VCCRTC (VBAT) well.

Table 37. RTC

Checklist Items	Recommendations	Reason/Effect
VBIAS	The VBIAS pin of the ICH2 is connected	For noise immunity on VBIAS signal
	to a 0.047 µF cap. See Figure 59
RTCX1	Connect a 32.768 kHz crystal oscillator	The ICH2 implements new internal oscillator
RTCX2	across these pins with a 10 MΩ resistor,	circuit as compared with the PIIX4, to reduce
	and use 12 pF decoupling caps at each	the power consumption. The external circuitry
	signal.	shown in Figure 59 is required to maintain
	RTCX1 may optionally be driven by an	RTC accuracy.
	external oscillator instead of a crystal.	The circuitry is required because the new RTC
	These signals are 1.8 V only and must	oscillator is sensitive to step voltage changes
	not be driven by a 3.3 V source.	in VCCRTC and VBIAS. A negative step
		voltage change of more than 100 mV will
		temporarily shut off the oscillator for hundreds
		of milliseconds.

Table 38. AC’97

Checklist Items	Recommendations	Reason/Effect
AC_SDOUT	Requires a jumper to 8.2 kΩ pull-up	This pin has a weak internal pull-down. To
	resistor. Should not be stuffed for default	properly detect a safe_mode condition, a
	operation.	strong pull-up is required to override this
		internal pull-down.
AC_SDIN[1],	Requires pads for weak 10 kΩ pull-	AC_SDIN[1:0] are inputs to an internal OR
AC_SDIN[0]	downs. Stuff resistor for unused	gate. If a pin is left floating, the output of the
	AC_SDIN signal or AC_SDIN signal	OR gate will be erroneous.
	going to the CNR connector.
	If there is no codec on the system board,
	then both AC_SDIN[1:0] should be pulled
	down externally with resistors to ground.
AC_BITCLK	No extra pull-down resistors are required.	When nothing is connected to the link, the
		BIOS must set a shut-off bit for the internal
		keeper resistors to be enabled. At that point,
		pull-ups/pull-downs are not required on any of
		the link signals.
AC_SYNC	No extra pull-down resistors are required.	Some implementations add termination for
		signal integrity. Platform specific.

130 Design Guide