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Chapter 8 BIOS ROM
Compaq Deskpro 4000N and 4000S Personal Computers
First Edition - September 1997
8-16
8.4.7 ACCESSING CMOS FEATURE BITS
The BIOS function INT 15, AX=E845h is a tri-modal call for accessing areas in non-volatile
memory used to store variables for various features.
INPUT:
EAX = E845h
BL = 0, Read
= 1, Write
BH = Value Read/to Write
CX = Feature Bits Number (refer to description box below)
DS:SI = Pointer to buffer passing multiple byte features
OUTPUT:
(Successful)
CF = 0
EAX = Reserved
BH = Value read (if a read was specified)
(Failure)
CF = 1
AH = 86h, Function not supported
CX Function
Default
Value
0000h PCI 2.1 Mode (Enabled) 1b
0001h Erase Eaze Keyboard (off) 00b
0002h Comm/IR Port Designation (Comm port) 0b
0003h No Rejection of SETs By PnP (reject SETs) 0b
0004h PCI VGA Snoop (snoop disabled) 0b
0005h PCI Bus Mastering BIOS Support (disabled) 0b
0006h Auto Prompt for Auto Setup (prompt for F1, F2, F10) 00b
0007h Mode 2 Configuration Support (enabled) 1b
0008h Secondary Hard Drive Controller Enabled (enabled) 1b
0009h Secondary Hard Drive Controller IRQ (IRQ15) 11b
000Ah Custom Drive Type #1 40 bits, all 0s
000Bh Custom Drive Type #2 40 bits, all 0s
000Ch Custom Drive Type #3 40 bits, all 0s
000Dh Custom Drive Type #4 40 bits, all 0s
000Eh POST Verbose/Terse or “Silent Boot” Mode (Terse) 1b
000Fh Drive Translation Mode (translate) 0b
0010h Mfg. Process Number Bytes 30 bits, [1]
0011h Administrator Password 72 bits, [1]
0012h Power-On Password 32 bits, [1]
0013h Ownership Tag 640 bits, [1]
0014h Warm Boot Password Mode (disabled) 0b
0015h Hood Lock (enabled) 1b
0016h Hood Removal (disabled) 00b
0017h USB Security (disabled) 0b
0018h Configurable Power Supply (legacy mode) 0b
0019h QuickBoot Mode (full boot always) 00000b
001Ah BBS IPL Order 76543210h
NOTE:
For full bit definitions refer to the
Compaq BIOS Technical Reference Guide
.
[1] Determined at runtime.