I/O Subsystem
R
210
Intel
®
855PM Chipset Platform Design Guide
Figure 115. Diode Circuit to Connect RTC External Battery
V
CCSUS
3_3
VccRTC
1.0uF
1K
A standby power supply should be used in a mobile system to provide continuous power to the RTC
when available, which will significantly increase the RTC battery life and thereby the RTC accuracy.
9.8.5.
RTC External RTCRST# Circuit
Figure 116. RTCRST# External Circuit for the ICH4-M RTC
V
CCSUS
3_3
VccRTC
1.0uF
1K
0.1uF
180K
RTCRST #
RTCRST#
CIRCUIT
DIODE/
BATTERY
CIRCUIT
The Intel 82801DBM ICH4-M RTC requires some additional external circuitry. The RTCRST# signal is
used to reset the RTC well. The external capacitor and the external resistor between RTCRST# and the
RTC battery (VBAT) were selected to create an RC time delay, such that RTCRST# will go high some