Rtc Crystal; External Circuitry In The 6300Esb Without Use Of Internal Rtc; External Circuitry For The 6300Esb Rtc - Intel 855GME Design Manual

®
Intel 855GME Chipset and Intel
®
Intel 6300ESB Design Guidelines
Figure 128.

External Circuitry in the 6300ESB Without Use of Internal RTC

9.11.1

RTC Crystal

The 6300ESB RTC module requires an external oscillating source of 32.768 kHz connected on the
RTCX1 and RTCX2 balls.
the 6300ESB RTC.
Figure 129.

External Circuitry for the 6300ESB RTC

3.3V Sus
Vbatt
NOTES:
1. The exact capacitor values for C1 and C2 must be based on the crystal maker recommendations. Typical
values for C1 and C2 are 18 pF, based on crystal load of 12.5 pF.
2. Reference designators are arbitrarily assigned.
3. 3.3 V Sus is active whenever the system is plugged in.
4. Vbatt is voltage provided by the battery.
5. VccRTC, RTCX1, and RTCX2 are 6300ESB pins.
6. VccRTC powers the 6300ESB RTC well.
7. RTCX1 is the input to the internal oscillator.
8. RTCX2 is the feedback for the external crystal.
9. VBIAS is used to provide a reference voltage, and this DC voltage sets a current, which is mirrored
throughout the oscillator and buffer circuitry.
10.Diodes must be Schottky
234
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6300ESB ICH Embedded Platform Design Guide
5 MΩ
RTCX1
Connection
32 kHz
Figure 129 shows the external circuitry that comprises the oscillator of
Ω
1 K
32.768 kHz
+
0.047 F
Internal
RTCX2
External
No
1 F
Xtal
C1 C2
18pF 18pF
C3
B1181-01
VCCRTC
RTCX2
R1
Ω
10 M
RTCX1
R2
Ω
10 M
VBIAS
B2846-01