Rtc External Circuit; Rtc External Circuitry; Rtc Connection When Not Using Internal Rtc - Intel Xeon Design Manual

9.6.1

RTC External Circuit

The ICH3-S RTC module requires an external oscillating source of 32.768 kHz connected on the
RTCX1 and RTCX2 balls.
oscillator of the ICH3-S RTC.
Figure 9-10. RTC External Circuitry
NOTES:
1. The exact capacitor values must be based on the crystal maker recommendation.
(Typical values for C1 and C2 are 18 pF for a crystal load of 12 pF.)
2. VCCRTC: Power for RTC Well
3. RTCX2: Feedback for the external crystal
4. RTCX1: Input to the internal oscillator
5. VBIAS: RTC BIAS Voltage – This pin is used to provide a reference voltage, and this DC voltage sets a
current, which is mirrored throughout the oscillator and buffer circuitry.
Note: Even if the ICH3-S internal RTC is not used, it is still necessary to supply clock inputs to RTCX1
and RTCX2 pins of the ICH3-S because other signals are gated with that clock in suspend modes.
However, in this case the frequency (32.768 kHz) of the clock inputs is not critical. A lower-cost
crystal can be used, or a single clock input can be driven into the RTCX1 pin with the RTCX2 pin
left as no connect;
Figure 9-11. RTC Connection When Not Using Internal RTC
Design Guide
Figure 9-10
3.3V Sus
32.768 kHz
C3
Vbatt 0.047 µF
Figure 9-11 illustrates this. This is not a validated configuration with ICH3-S.
RTCX1
32 KHz
documents the external circuitry that comprises the
1 µF
C1
18 pF
Xtal
C2
18 pF
5 MΩ
RTCX2
No
Connection
I/O Controller Hub
VCCRTC
RTCX2
R1
10 M Ω
RTCX1
R2
10 M Ω
VBIAS
Internal
External
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