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Chapter 4 System Support
4.6 REAL-TIME CLOCK AND CONFIGURATION MEMORY
d
e RTC uses the first 14 bytes (00-0Dh) of the
andard memory area. All locations of the standard memory area (00-7Fh) can be directly
ns through I/O ports
lithium 3-VDC battery is used for maintaining the RTC and configuration memory while the
system is powered down. During system o -Ored circuit allows the RTC and
configuration memory to dra ery is located in a battery
h h oard and has a life expe fou ears. When the battery has
expired it is replaced with a Renata CR2032 or equivalent 3- ttery.
4.6.1
ARI
The content emory (includ he Power-On Password) can be cleared by the
f ing pr
1 urn of
2 isconn he o /or sy
3 emove ins at no LE
lumina
4 ess an n e system
5 eplace
6 econn e outl syste
the unit on.
To clear
The Real-time clock (RTC) and configuration memory (also referred to as “CMOS”) functions are
provided by the 82801 ICH2 component and is MC146818-compatible. As shown in the
following figure, the 82801 ICH2 component provides 256 bytes of battery-backed RAM divide
into two 128-byte configuration memory areas. Th
st
accessed using conventional OUT and IN assembly language instructio
70h/71h, although the suggested method is to use the INT15 AX=E823h BIOS call.
Extended Config.
FFh
Register B
Register C
0Bh
0Ch
Seconds (Timer)
Seconds (Alarm)
00h
01h
Figure 4-10. Configuration Memory Map
C
M
OS
RTC Area
(14 bytes)
Standard Config.
Memory Area
(114 bytes)
Memory Area
00h
0Dh
0Eh
Minutes (Timer)
larm)
Hours (Timer)
Minutes (Alarm)
Register A
Register D
(128 bytes)
Month
Year
08h
09h
80h
Date of Month
07h
7Fh
Day of Week
06h
Hours (A
05h
82801
02h
03h
04h
0Ah
0Dh
A
peration a wire
w power from the power supply. The batt
older on t e system b ctancy of r to eight y
VDC lithium ba
CLE NG CMOS
s of configuration m ing t
ollow ocedure:
. T f the unit.
. D ect the AC power cord from t utlet and stem unit.
. R the chassis hood (cover) and ure th Ds on the system board are
il ted.
. Pr d release the CMOS clear butto on th board.
. R the chassis hood (cover).
. R ect the AC power cord to th et and/or m unit.
7. Turn
only the Power-On Password refer to section 4.7.1.1.
Compaq Evo and Workstation Personal Computers
Featuring the Intel Pentium 4 Processor
Second Edition – January 2003
4-24