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Chapter 4 System Support
Compaq Deskpro EXS and Workstation 300 Personal Computers
Featuring the Intel Pentium 4 Processor
First Edition - December 2000
4-20
4.5 SYSTEM CLOCK DISTRIBUTION
These systems use an Intel CK-type clock generator and crystal for generating the clock signals
required by the system board components. Table 4-10 lists the system board clock signals and how
they are distributed.
Table 4-10. Clock Generation and Distribution
Table 4-10
Clock Generation and Distribution
Frequncy Source Destination
400 MHz MCH Processor, RIMM sockets
100 MHz CK MCH
66 MHz CK MCH, ICH2, AGP slot
48 MHz CK ICH2, I/O Cntlr.
33 MHz CK Processor, ICH2, PCI Slots
14.31818 MHz Crystal CK
Certain clock outputs are turned off during reduced power modes to conserve energy. Clock output
control is handled through the SMBus interface by BIOS.
4.6 REAL-TIME CLOCK AND CONFIGURATION MEMORY
The Real-time clock (RTC) and configuration memory (also referred to as “CMOS”) functions are
provided by the 82801 ICH component and is MC146818-compatible. As shown in the following
figure, the 82801 ICH component provides 256 bytes of battery-backed RAM divided into two
128-byte configuration memory areas. The RTC uses the first 14 bytes (00-0Dh) of the standard
memory area. All locations of the standard memory area (00-7Fh) can be directly accessed using
conventional OUT and IN assembly language instructions through I/O ports 70h/71h, although the
suggested method is to use the INT15 AX=E823h BIOS call.
Figure 4-10. Configuration Memory Map
A lithium 3-VDC battery is used for maintaining the RTC and configuration memory while the
system is powered down. The battery is located in a battery holder on the system board is replaced
with a Renata CR2032 or equivalent 3-VDC lithium battery.
RTC Area
(14 bytes)
Standard Config.
Memory Area
(114 bytes)
Extended Config.
Memory Area
(128 bytes)
00h
0Dh
0Eh
80h
FFh
7Fh
Seconds (Timer)
Minutes (Timer)
Seconds (Alarm)
Hours (Alarm)
Hours (Timer)
Minutes (Alarm)
Day of Week
Date of Month
Month
Year
Register A
Register B
Register C
Register D
00h
0Bh
01h
02h
03h
04h
05h
06h
07h
08h
09h
0Ah
0Dh
0Ch
82801
C
M
OS