Compaq 4000N - Manual (Page 86)

Chapter 4 System Support
Compaq Deskpro 4000N and 4000S Personal Computers
First Edition - September 1997
4-44
4.7 SYSTEM MANAGEMENT SUPPORT
This section describes the hardware support of functions involving security, safety, identification,
and power consumption of the system. System management functions are handled largely
through a Compaq-proprietary ASIC. Most functions are controlled through registers (Table 4-
19) accessed using the indexed method through I/O ports 0C50h (index) and 0C51h (Data).
Table 4–19. System Management Control Registers
Table 4-19.
System Management Control Registers
Index Function
00h Identification
02h Temperature Status / Clear
03h Temperature Interrupt / SMI Enable
05h Power On LED Blink Control
12h General Purpose Open Collector (GPOC) Bits
13h Secured GPOC Bits
20h Power Button Control
21h SMI / SCI Source
22h SMI / SCI Mapping
30h REQ/GNT Control
80h-89h Reserved
NOTE: System management functions are handled by BIOS and the Setup utility. The
information in the following subsections is intended only for clarification of system operations.
4.7.1 FLASH ROM WRITE PROTECT
The system BIOS firmware is contained in a flash ROM device that can be re-written with
updated code if necessary. The ROM is write-protected with a Black Box* security feature. The
Black Box feature uses the Administrator password to protect against unauthorized writes to the
flash ROM. During the boot sequence, the BIOS checks for the presence of the ROMPAQ
diskette. If ROMPAQ is detected and the password is locked into the Black Box with the Protect
Resources command, an Access Resources command followed by Administrator password entry
must occur before the ROM can be flashed. If the Permanently Lock Resources command has
been invoked, the power must be cycled before the ROM can be flashed. The system ROM is
write-protected as follows:
Start Addr. End Addr. Data Type Protection
C0000h EFFFFh Option ROM Password write-protected
F0000h F7FFFh System BIOS Password write-protected
F8000h F9FFFh ESCD Never write-protected
FA000h FFFFFh Boot Block Always write-protected
The flashing functions are handled using the INT15 AX-E822h BIOS interface.
* Black Box logic Compaq-proprietary and controlled exclusively through firmware in the BIOS ROM.