HP Compaq d330 DT User Manual

Chapter 4 System Support
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 component and is MC146818-compatible. As shown in the following
figure, the 82801 ICH5 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.
ton on the system board.
power cord to the outlet and/or system unit.
. Turn the unit on.
To clear only the Power-On Password refer to section 4.7.1.1.
RTC Area
(14 bytes)
Standard Config.
M emory Area
(114 bytes)
Extended Config.
Memory Area
(128 bytes)
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
82801
0Bh
0Dh
0Ch
00h
01h
02h
03h
04h
05h
06h
07h
08h
09h
0Ah
FFh
80h
7Fh
0Dh
0Eh
00h
C
M
OS
Figure 4-11. Configuration Memory Map
A lithium 3-VDC battery is used for maintaining the RTC and configuration memory while the
system is powered down. During system operation a wire-Ored circuit allows the RTC and
configuration memory to draw power from the power supply. The battery is located in a battery
holder on the system board and has a life expectancy of four to eight years. When the battery has
expired it is replaced with a Renata CR2032 or equivalent 3-VDC lithium battery.
4.6.1 CLEARING CMOS
The contents of configuration memory (including the Power-On Password) can be cleared by the
following procedure:
1. Turn off the unit.
2. Disconnect the AC power cord from the outlet and/or system unit.
3. Remove the chassis hood (cover) and insure that no LEDs on the system board are
illuminated.
4. Press and release the CMOS clear but
5. Replace the chassis hood (cover).
6. Reconnect the AC
7
hp compaq d330 and d530 Series of Personal Computers
Featuring the Intel Pentium 4 Processor
First Edition – June 2003
4-22

HP Compaq d330 DT Specifications

General

Brand	HP
Model	Compaq d330 DT
Category	Desktop
Language	English