Intel Pentium 4 User Manual

I/O Controller Hub 2
R
Intel
®
Pentium
®
4 Processor / Intel
®
850 Chipset Family Platform Design Guide 157
9.8 RTC
The ICH2 contains a real time clock (RTC) with 256 bytes of battery backed SRAM. The internal
RTC module provides two key functions: keeping date and time and storing system data in its
RAM when the system is powered down.
This section will present the recommended hookup for the RTC circuit for the ICH2. This circuit
is not the same as the circuit used for the PIIX4.
9.8.1 RTC Crystal
The ICH2 RTC module requires an external oscillating source of 32.768 kHz connected on the
RTCX1 and RTCX2 pins. Figure 113 shows the external circuitry that comprises the oscillator of
the ICH2 RTC.
Figure 113. External Circuitry for the Intel
®
ICH2 RTC
C3
1
VCC3_3SBY
1 kΩ
Vbatt_RTC
1 k
Ω
C1
470 pF
32768 Hz
Xtal
R1
10 M
Ω
R2
10 M
Ω
C2
1
1 µF
VCCRTC
2
RTCX2
3
RTCX1
4
VBIAS
5
VSS
6
RTC_osc_circ
NOTES:
1. The exact capacitor value needs to based on what the crystal maker recommends.
2. V
CC
RTC: Power for RTC Well
3.
RTCX2: Crystal Input 2 – Connected to the 32.768 kHz crystal.
4. RTCX1: Crystal Input 1 – Connected to the 32.768 kHz crystal.
5. VBIAS: RTC BIAS Voltage – This pin is used to provide a reference voltage, and this DC voltage sets a
current that is mirrored throughout the oscillator and buffer circuitry.
6. VSS: Ground

Intel Pentium 4 Specifications

General

Brand	Intel
Model	Pentium 4
Category	Computer Hardware
Language	English