Intel 820E Benutzerhandbuch

Design Guide 

 

99 

A standby power supply should be used in a desktop system to provide continuous power to the RTC 
when available, which will significantly increase the RTC battery life and thereby increase the RTC 
accuracy. 

The ICH2 RTC requires 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 (V

BAT

) 

were selected to create an RC time delay, such that RTCRST# will go high some time after the battery 
voltage becomes valid. The RC time delay should be within the range 10 ms–20 ms. When RTCRST# is 
asserted, bit 2 (RTC_PWR_STS) in the GEN_PMCON_3 (General PM Configuration 3) register is set to 
1 and remains set until cleared by software. As a result, when the system boots, the BIOS knows that the 
RTC battery has been removed.  

VCC3_3SBY

  VccRTC

1.0 µF

1 k

Ω

2.2 µF

8.2 k

Ω

RTCRST#

RTCRST

Circuit

Diode/

Battery

Circuit

rtc_rtcrst_ich

 

This RTCRST# circuit is combined with the diode circuit (Figure 60. Diode Circuit Connecting RTC 
External Battery), which allows the RTC well to be powered by the battery when system power is 
unavailable. Figure 59 is an example of the circuit used in conjunction with the external diode circuit.