16.7.10. Rtc Circuitry; Figure 157. External Circuitry For The Rtc - Intel 855GM Design Manual

Platform Design Checklist

16.7.10. RTC Circuitry

Pin Name
Pull-up/Pull-down
RTCRST# 180 k Ω pull-up to
VccRTC
CLK_RTCX1,
CLK_RTCX2
CLK_VBIAS

Figure 157. External Circuitry for the RTC

3.3V Sus
1k Ω
Vbatt
Notes
Reference Designators Arbitrarily Assigned
3.3V Sus is Active Whenever System Plugged In
Vbatt is Voltage Provided By Battery
308
System In Series
1 K Ω
0.047 µF
32.768 kHz
C3
0.047uF
Notes
RTCRST# requires 18-25 ms delay. Use a 0.1 µF cap to
ground Pull up with 180 k Ω resistor. Any resistor or capacitor
combination that yields a time constant is acceptable.
Connect a 32.768 kHZ crystal oscillator across these pins
with a 10 M Ω resistor and a decoupling cap at each signal.
Values for C1 and C2 are dependent on crystal.
See Figure 157.
Connect to CLK_RTCX1 through a 10 M Ω resistor. Connect
to VBATT through a 1 k Ω in series with a 0.047 µF capacitor.
1uF
Xtal
C1 C2
VBIAS, VCCRTC, RTCX1, and RTCX2 are ICH4-M pins
VBIAS is used to bias the ICH4 Internal Oscillator
VCCRTC powers the RTC well of the ICH4-M
RTCX1 is the Input to the Internal Oscillator
RTCX2 is the feedback for the external crystal
®
Intel 855GM/855GME Chipset Platform Design Guide
R
VCCRTC
RTCX2
R1
10M Ω
RTCX1
R2
10M Ω
VBIAS