AMIBIOS 98Technical Reference
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`MAN-BIOS98-TR
`5/1/98
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`EX 1013
`IPR of Pat. No. 6,892,304
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`© Copyright 1998 American Megatrends, Inc.
`All rights reserved.
`American Megatrends, Inc.
`6145F North Belt Parkway
`Norcross, GA 30071
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`This publication contains proprietary information which is protected by copyright. No part of thispublication may be reproduced, transcribed, stored in a retrieval system, translated to any language orcomputer language, or transmitted in any form whatsoever without the prior written consent of thepublisher, American Megatrends, Inc.Limited WarrantyNo warranties are made, either express or implied, with regard to the contents of this work, itsmerchantability, or fitness for a particular use.American Megatrends assumes no responsibility for errors and omissions or for the uses made of thematerial contained herein or reader decisions based on such use.Limitations of Liability In no event shall American Megatrends be held liable for any loss, expenses, or damages of any kindwhatsoever, whether direct, special, indirect, incidental, or consequential, arising from or arising out ofthe use or inability to use the contents of this manual.
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`TrademarksAmerican Megatrends acknowledges the following trademarks:
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`Intel, Pentium, and Pentium Pro are registered trademarks of Intel Corporation.
`AMD is a registered trademark of Advanced Micro Devices, Inc.
`Cyrix is a registered trademark of Cyrix Corporation.
`NCR is a registered trademark of National Cash register Corporation.
`DesqView is a registered trademark of Quarterdeck Office Systems, Inc.
`MS-DOS, Xenix, and Microsoft are registered trademarks of Microsoft Corporation. Microsoft Windows, Windows 95, and Windows NT
`are trademarks of Microsoft Corporation.
`Unix is a registered trademark of American Telephone and Telegraph Company Bell Laboratories.
`IBM, AT, VGA, EGA, XGA, PS/2, MCA, OS/2, and MicroChannel are registered trademarks of International Business Machines
`Corporation. PC-DOS, XT, and CGA are trademarks of International Business Machines Corporation.
`TI is a registered trademark of Texas Instruments Corporation.
`SMC is a registered trademark of Standard Microsystems Corporation.
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`Revision History
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`Initial release.
`4/92
`10/92 Revised for 6/6/92 core AMIBIOS.
`12/92 Corrected minor errors.
`5/24/93 Added APM, PCI, and Socket Service BIOS function documentation.
`8/1/93 Updated to PCMCIA Version 2.00 Socket Service specifications.
`9/1/93 Added new INT 16h functions for Flash EPROM.
`4/1/94 Added PnP functions and new POST checkpoint codes.
`10/1/94 Updated for 07/25/94 core BIOS.
`10/31/95 Updated for AMIBIOS 95.
`5/6/96 Updated for V6.24 of 7/15/95 core AMIBIOS.
`6/19/97 Converted to Microsoft Word Format.
`7/9/97 Added additional PCI functions.
`2/25/98 Corrected error in PCI function register use and INT 15h Function E801h use.
`5/1/98 Added INT 15h Function 24h description.
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`ii AMIBIOS 98 Technical Reference
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`Preface iii3Table of Contents1 Introduction.................................................................1Parts of the System ROM BIOS..............................................................3Types of BIOS........................................................................................52 System Memory Map..................................................9Conventional Memory Map....................................................................9Upper Memory Map.............................................................................103 BIOS Data Area.........................................................114 BIOS Data..................................................................19APM Information.................................................................................19Location of AMIBIOS Routines............................................................21ROM Compatibility Table....................................................................22Floppy Disk Drive Parameters..............................................................23Summary of Default Settings for Floppy Drives....................................26Hard Disk Parameter Table...................................................................27Hard Disk Drive Types.........................................................................29Enhanced IDE Hard Disk Drive Parameters.........................................31Extended Drive Parameter Table..........................................................32IDE LBA Mode....................................................................................34Hard Disk Drive Data Transfer Rates...................................................34Video Parameter Table.........................................................................35System Configuration Data...................................................................35Serial Port Data Transmission Rates.....................................................36ROM Compatibility Information...........................................................37ROM Compatibility Table....................................................................385 CMOS RAM................................................................39AMIBIOS 98 CMOS RAM Map...........................................................406 I/O Port Addresses....................................................43Accessing I/O Ports..............................................................................44ISA and EISA I/O Port Assignments....................................................44EISA Adapter Card Compressed ID......................................................61Monochrome Video I/O Ports...............................................................62CGA Video I/O Ports............................................................................637 Power On Self Test...................................................65POST Phases........................................................................................65POST Functions...................................................................................66System Boot.........................................................................................72POST Checkpoint Codes......................................................................738 Using Interrupts........................................................81Types of Interrupts...............................................................................82
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`iv AMIBIOS 98 Technical ReferenceTable of Contents, Continued9 System BIOS Interrupts............................................89INT 00h Divide by Zero........................................................................92INT 01h Single Stepping......................................................................92INT 02h Nonmaskable Interrupt (NMI)................................................93INT 03h Breakpoint.............................................................................94INT 04h Overflow Error.......................................................................94INT 05h Print Screen...........................................................................94INT 06h Invalid Op Code.....................................................................95INT 07h Coprocessor Not Available.....................................................95INT 08h Timer Interrupt (IRQ0)..........................................................96INT 09h Keyboard Interrupt (IRQ1).....................................................97INT 10h Video Service.......................................................................100INT 11h Return System Configuration...............................................111INT 12h Return Total Memory Size...................................................111INT 13h Hard Disk Service................................................................112INT 13h Floppy Disk Service.............................................................137INT 14h Serial Communications Service............................................146INT 15h System Services....................................................................156INT 16h Keyboard Service.................................................................215INT 17h Parallel Port Service.............................................................233INT 18h ROM Basic...........................................................................235INT 19h System Boot Control.............................................................236INT 1Ah Real Time Clock Service.....................................................238INT 1Ah Socket Services....................................................................247INT 1Ah PCI Service.........................................................................287INT 1Ah Plug and Play Service..........................................................304Plug and Play Option ROMs...............................................................318INT 1Ah DMI BIOS Interface............................................................324INT 1Bh <Ctrl> <Break>...................................................................334INT 1Ch Periodic Timer Interrupt......................................................334INT 1Dh Video Parameter Table........................................................334INT 1Eh Floppy Disk Parameter Table...............................................335INT 1Fh Video Graphics Characters...................................................335INT 4Ah Alarm ISR...........................................................................335INT 70h Real Time Clock Interrupt (IRQ8)........................................336INT 71h IRQ9....................................................................................336INT 74h PS/2 Mouse Interrupt (IRQ12)..............................................336INT 75h Math Coprocessor Interrupt (IRQ13)....................................337INT 76h AT Hard Disk Drive Interrupt (IRQ14)................................337INT 77h Software Suspend Request (IRQ15)......................................33710 Power Management AMIBIOS..............................33911 EISA Overview.......................................................345
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`Preface v5Table of Contents, Continued12 DMI Data Structures..............................................359Accessing DMI Structures..................................................................360DMI BIOS Information......................................................................361DMI System Information (Type 1)......................................................363DMI Motherboard Information (Type 2).............................................363DMI Chassis Information (Type 3).....................................................364DMI Processor Information (Type 4)..................................................365DMI Memory Controller Information (Type 5)...................................367DMI Memory Module Information (Type 6).......................................369DMI Cache Information Structure (Type 7)........................................371DMI Port Connector Information (Type 8)..........................................373DMI System Slots (Type 9).................................................................375DMI Onboard Device Information (Type 10)......................................376DMI OEM Strings (Type 11)..............................................................377DMI Group Associations (Type 14)....................................................378DMI System Event Log (Type 15)......................................................378DMI System Event Log......................................................................38013 AMIBIOS Multiprocessor Support.......................383APIC Support.....................................................................................383Intel Multiprocessor Specification.......................................................385MPS System BIOS Multiprocessor Support........................................387A AMIBIOS Error Messages and Beep Codes.........391Displayed Fatal Error Messages..........................................................392EISA BIOS Error Messages................................................................394ISA NMI BIOS Messages...................................................................394EISA NMI BIOS Error Messages.......................................................395B AMIBIOS Identification Strings..............................397AMIBIOS Identification String Line 2................................................398AMIBIOS Identification String Line 3................................................398AMI BIOS and AMI BIOS Plus Identification Strings........................399Index...........................................................................401
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`vi AMIBIOS 98 Technical ReferencePrefaceTo the ReaderThis manual provides technical details about the operation of AMIBIOS forISA and EISA PCI, Plug and Play, APM-aware, and DMI-aware computers.We assume are familiar with the Intel x86 architecture, x86 assemblerlanguage, and both ISA and EISA system architecture.Technical Support AMI only provides technical support for AMI products purchased directlyfrom AMI or from an AMI-authorized reseller.If…then…You purchased this product from AMI orfrom a certified AMI reseller,Call AMI technical support at 770-246-8600. Please be prepared to specify theserial number of the product.This AMI product was installed as partof a system manufactured by a companyother than AMI or you purchased anAMI product from an unauthorizedreseller.Call the technical support department ofthe computer manufacturer or theunauthorized reseller. AMI does notprovide direct technical support in thiscase.Web SiteYou can download technical and marketing information from our web site. TheURL is:http://www.ami.comTechnical Support Email You can send email to the American Megatrends technical supportdepartment at the following address:Support@ami.com
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`Chapter 1 Introduction 11IntroductionThe architecture of ISA and EISA computers is layered. The lowest layer is thecomputer — the hardware itself. The highest layer is the applications softwarethat the user interfaces with. Systems software lies between applicationssoftware and hardware.Systems software can consist of several elements: the operating system kernel,the operating system shell, and additional device drivers. Operatingenvironments (Microsoft® Windows™, for example) exist in a layer betweenthe operating system and applications software, as do multitasking supervisorsor DOS extenders like Desqview®.The BIOS (Basic Input/Output System) is a collection of routines between thehardware and the systems software. The BIOS ROM contains hard diskutilities, device drivers, interrupt service routines, and other code and databetween the system hardware and the systems software.New BIOS Features and Functions In the last year, system BIOS has taken on an additionalnew layer of functionality. The EPA Green PC, PCI (Peripheral ComponentInterconnect), Plug and Play, APM (Advanced Power Management), and DMI(Desktop Management Interface) initiatives have all specified many additionalfunctions that must be performed by the system BIOS in ISA and EISAcomputers. This manual has been updated to include all BIOS functionsrequired by these new specifications and implemented in AMIBIOS.In This Chapter The following topics are discussed in this chapter:
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`BIOS as Interface,
`Parts of the ROM BIOS, and
`Types of BIOS.
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`2 AMIBIOS 98 Technical ReferenceThe BIOS as InterfaceThe BIOS is the software layer between the systems software and the hardwarein ISA and EISA systems. The BIOS works in two directions. One part of theBIOS receives and processes requests from programs to perform the standardBIOS I/O services. The mechanism for these requests is called an interrupt,discussed in detail later in this manual. Interrupts are invoked by softwareprograms. In an assembler program, the INT mnemonic is followed by aninterrupt number that specifies the type of service and a function number thatspecifies the exact service to be performed. For example:MOVAH,00h;specifies function 00h get ;character from keyboardINT 16h;requests INT 16h Keyboard ServiceBIOS and the Hardware The other side of the BIOS communicates with the hardware (videodisplay, disk drives, keyboard, serial and parallel ports, and so on) in thelanguage and codes used by each device. This side of the BIOS also handlesany hardware device-generated interrupts. For example, when a key is pressedon the keyboard, a hardware interrupt (IRQ1) is generated. The BIOS INT 09hinterrupt service routine is called to handle this interrupt. The following figureillustrates the role that the system BIOS plays.
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`the BIOS Setup utility.The following graphic depicts these elements:System BIOSThe BIOS is a part of the code stored in ROM that is in active use the entiretime that a computer is on. The ROM BIOS provides the fundamental servicesneeded for the proper operation.Cont’d
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`Chapter 1 Introduction 33Parts of the System ROM BIOSThe system ROM elements in a computer with an AMIBIOS are:
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`POST,
`the ROM BIOS itself, and
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`POSTThe ROM BIOS includes BIOS Power-On Self Test diagnostic and bootingcode that tests the computer components, initializes certain data structures, andboots DOS. POST performs several functions:
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`executes a diagnostic and reliability test of the computer, the ROMprograms, and RAM,
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`initializes the chips and the standard parts of the computer and places arecord of the system configuration in CMOS RAM and in low systemmemory,
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`boots the operating system.See the BIOS POST discussion in Chapter 5 for additional information aboutPOST.AMIBIOS Setup Utility AMIBIOS Setup stores system configuration values in CMOS RAM.Type of SetupDescriptionStandard SetupSets the hard disk drive type, type of floppy drives andmonitor, and the day, date, and time.Advanced SetupSets more technical system values, such as the typematic rate,memory test patterns, cache setting, etc.Chipset SetupSets system configuration data that is specific to the chipset-used on the motherboard. The Chipset Setup options are highlytechnical. The settings for Chipset Setup options are usuallyspecific to the motherboard design and should not be changed.PCI/PnP SetupSets system configuration data that relates to the use of the PCIbus and the Plug and Play configuration.PowerManagementSetupPower Management Setup configures options related to powerconservation and use.Peripheral SetupConfigures options such as the floppy and IDE controllers onthe motherboard, the base I/O port addresses for the serial andparallel ports, and other options related to the I/O controller.WINBIOS® Setup American Megatrends introduced the WINBIOS Setup utility in early 1994.It has been an instant hit because of its extremely easy-to-use MicrosoftWindows-like graphical interface.
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`4 AMIBIOS 98 Technical ReferenceParts of the System ROM BIOS,
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`sets up the interrupt vector table,
`detects optional equipment, and
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`optional option ROM BIOSes.This manual describes the system BIOS features and functions. The video BIOSis best discussed in the context of EGA®, VGA®, and XGA® video standards,which all require a separate BIOS.System BIOS The system BIOS tests the computer components, loads (bootstraps) theoperating system, and remains active for requests by the operating system toactivate device drivers that service the hardware components. The BIOS takesthe instructions from the operating system and translates these commands tothe exact instructions that the hardware itself understands. The BIOS maintainsdata about the components. When a component is unable to perform, the BIOSreports it to the operating system.An AMIBIOS system ROM BIOS with all features enabled is usually 128 KBlong and resides at E0000h – FFFFFh in both EISA and ISA computers. Thisarea is addressed to ROM but can be shadowed to RAM. ROM operates atabout 120 – 180 ns; RAM usually operates at 60 – 100 ns. System BIOS arealmost universally stored on flash EPROMs now so they can be upgradedeasily.The system BIOS now typically includes PCI, APM, Plug and Play, DMI,enhanced IDE, WINBIOS Setup utility, and Green PC support. NewerAMIBIOS support the Extended System Configuration Data Specification(ESCD).Cont’d
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`Chapter 1 Introduction 55Types of BIOSIn ISA and EISA computers, the types of BIOS (Basic Input Output System)include:
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`the system BIOS,
`the video BIOS, and
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`Video BIOSAll ISA and EISA computers that use EGA, VGA, or XGA have video BIOSes.The system BIOS video service only handles the most basic video functions.Advanced video modes must be translated via a video BIOS, usually installedon the video adapter card.Option ROM BIOS Many adapter cards have code in ROM. For example, Ethernet networkadapter cards have a ROM that assists in translating Ethernet commands tocode the computer can understand and vice versa. Option ROM resides betweenC8000h and EFFFFh. This area also can be shadowed in AMIBIOS to speedthe operation of the devices that have option ROMs, provided that themotherboard or chipset supports option ROM shadowing. Option ROM is alsocalled Option ROM.Specifications Supported In general, AMIBIOS supports the latest specification for each of thefollowing standards:
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`6 AMIBIOS 98 Technical ReferenceTypes of BIOS,
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`Plug and Play,
`DMI,
`Extended System Configuration Data,
`EISA,
`PCI,
`ACPI,
`AGP,
`SMART,
`IEEE 1394 Firewire,
`Ultra DMA,
`all Enhanced IDE, ATA and ATAPI standards,
`IrDA,
`MPS,
`Universal Serial Bus,
`APM (Advanced Power Management), and
`EPA Green PC.
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`Chapter 1 Introduction 77AMIBIOS UtilitiesUtilityAudience DescriptionAMIBIOSSetupend usersThis character-based utility is provided with Hi-FlexAMIBIOS. It configures the computer and managesthe NVRAM (Non-Volatile Random Access Memory)in the computer. See the Hi-Flex AMIBIOS User'sGuide for additional information.WINBIOSSetupend usersThis graphically-oriented utility is provided withAMIBIOS. It configures the computer and managesthe NVRAM (Non-Volatile Random Access Memory)in the computer. See the AMIBIOS User's Guide forthe 10/10/94 (or later) core AMIBIOS for additionalinformation.SystemConfigurationUtilityend usersThe SCU configures both EISA and Plug and Playcomputers. See the System Configuration UtilityUser's Guide for additional information.AMIBCPBIOScustomersThe BIOS Configuration Program allows computermanufacturers to customize AMIBIOS.AMIEmbedBIOScustomersAllows OEMs to embed option ROMs in AMIBIOS.Typical applications include adding SCSI BIOS,network BIOS, or VGA BIOS to AMIBIOS.PCI RouterBIOScustomersAllows OEMs to customize the IRQ routing for PCI-based motherboards. PCI provides four hardwareinterrupts that can be used in many ways. Ofnecessity, motherboard IRQ routing must be differentin each motherboard design. PCI Route allowsmotherboard designers to customize the IRQ routingin a standard AMIBIOS for a specific motherboardAMIFlashBIOScustomersAMIFlash allows OEMs and end users to update theBIOS in a computer where the system BIOS is storedon a flash EPROM.DMI WizardDMI Wizard95BIOScustomersDMI Wizard is a DOS utility with a graphicalinterface that allows you to display and modify DMI(Desktop Management Interface) system configurationdata in any DMI-aware system BIOS ROM or BIOS.ROM file. DMI Wizard 95 is a Windows 95 utilitythat performs the same functions.CPUSelectBIOScustomersAllows OEMs to customize CPU support in anAMIBIOS.
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`Chapter 2 System Memory Map 992System Memory MapConventional Memory MapThe following table shows the use of the first megabyte of memory.
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`An extra 64K accessed
`via an EMS driver. Controlled
`by either DOS, Windows, a
`Network, or Desqview.
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`10 AMIBIOS 98 Technical ReferenceUpper Memory MapUpperMemoryBlocksB8000hHighMemoryArea(64KB)ISASystemBIOS(64KB)EISASystemBIOS,Network,orAdaptorROMs(64KB)AdaptorROM(64KB)EGAandVGAVideoBIOS(32KB)32KBVideoBufferforCGA,EGAcolor,andVGAcolor.32KBVideoBufferforMDA,CGAmonochrome,andVGAmonochrome.EGAandVGAVideoBuffer(128KB)AdaptorROM(32KB)VideoMemory(64KB)BFFFFhB7FFFhB0000hAFFFFhA0000h
`FFFFFhEFFFFhC8FFFhF0000hE0000hC8000hBFFFFhA0000hDFFFFhD0000hC7FFFhC0000h640K1024K
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`Chapter 3 BIOS Data Area 11113BIOS Data AreaWhen an ISA or EISA computer is powered-on, the BIOS Data Area is createdat location 000400h. It is 256 bytes long (000400 – 0004FFh) and containsinformation about the system environment. This information can be accessedand changed by any program. Much of the operation of ISA and EISAcomputers is controlled by this data. This data is loaded by POST (the BIOSPower-On Self Test) during startup. The following table lists the contents of allBIOS data area locations. All addresses are offsets from 000400h.OffsetBIOSService Description00hINT 14hSerial Port (COM) 1 — least significant byte.01hINT 14hSerial Port (COM) 1 — most significant byte.02hINT 14hSerial Port (COM) 2 — least significant byte.03hINT 14hSerial Port (COM) 2 — most significant byte.04hINT 14hSerial Port (COM) 3 — least significant byte.05hINT 14hSerial Port (COM) 3 — most significant byte.06hINT 14hSerial Port (COM) 4 — least significant byte.07hINT 14hSerial Port (COM) 4 — most significant byte.08hINT 17hParallel Port (LPT) 1 — least significant byte09hINT 17hParallel Port (LPT) 1 — most significant byte0AhINT 17hParallel Port (LPT) 2 — least significant byte0BhINT 17hParallel Port (LPT) 2 — most significant byte0ChINT 17hParallel Port (LPT) 3 — least significant byte0DhINT 17hParallel Port (LPT) 3 — most significant byte0EhPOSTExtended BIOS data area segment — least significant byte0FhPOSTExtended BIOS data area segment — most significant byte10h–11hINT 11hEquipment listBits 15–14Number of parallel adapters00None installed01One installed10Two installed11Three installedBit 12Game port installed0No1YesBits 11–9Serial adapters installed000None installed001One installed010Two installed011Three installed100Four installedBits 7–6Number of floppy disk drives.00One drive01Two drivesBits 5–4Initial video mode00EGA/VGA0140 x 25 CGA color1080 x 25 CGA color1180x25 MonochromeBit 2PS/2-type pointing device1PresentBit 1Math coprocessor1PresentBit 0Floppy disk drive A:1Present12hPOSTInterrupt flag used in POST.13hINT 12hMemory size in KB — least significant byte.14hINT 12hMemory size in KB — most significant byte.
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`12 AMIBIOS 98 Technical ReferenceOffsetBIOSService Description15h–16hReserved17hINT 16hKeyboard status byteBit 7Insert Mode is on if set.Bit 6<Caps Lock> Key on if set.Bit 5<Num Lock> key on if set.Bit 4<Scroll Lock> Key on if set.Bit 3<Alt> key pressed if set.Bit 2<Ctrl> key pressed if set.Bit 1Left <Shift> Key pressed if set.Bit 0Right <Shift> Key pressed if set.18hINT 16hExtended keyboard status byteBit 7<Ins> key pressed if set.Bit 6<Caps Lock> key pressed if set.Bit 5<Num Lock> key pressed if set.Bit 4<Scroll Lock> pressed if set.Bit 3<Ctrl><Num Lock> state activeBit 2<SysReq> key pressed if set.Bit 1Left <Alt> key pressed if set.Bit 0Left <Ctrl> key pressed if set.19hReserved1Ah–1BhINT 16hPointer to the address of the next character in the keyboardbuffer.1Ch–1DhINT 16hPointer to the address of the last character in the keyboardbuffer.1Eh–3DhINT 16hKeyboard buffer (32 bytes). If the address in 1Ah is thesame as the address in 1Ch, the buffer is empty. If theaddress in 1Ch is two bytes from the address in 1Ah, thebuffer is full.3EhINT 13hFloppy disk drive calibration statusBit 7Diskette hardware interrupt occurred0No1YesBits 6–4Reserved. Should be 00h.Bit 1Floppy Drive B: needs recalibration if 0.Bit 0Floppy Drive A: needs recalibration if 0.3FhINT 13hFloppy disk drive motor statusBit 70 Current operation is Write or Format.1 Current operation is Read or Verify.Bits 5–4Drive select00 Drive A: select01 Drive B: selectBits 3–2ReservedBit 11Drive A: motor is on.Bit 01Drive B: motor is on.40hINT 13hFloppy disk drive motor timeoutThis is decremented by one 18.2 times per second (via theINT 08h timer interrupt). When the value becomes zero, thedrive motor is powered off. The value refers to the last diskdrive accessed.
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`Chapter 3 BIOS Data Area 1313OffsetBIOSService Description41hINT 13hFloppy disk drive status. These values are valid for the lastfloppy disk drive accessed.Bit 7Drive not ready if set.Bit 6Seek error detected if set.Bit 5Floppy disk controller failed if set.Bits 4–0Error codes00hNo error occurred01hIllegal function requested02hAddress mark not found03hWrite protect error04hSector not found06hDrive door was opened08hDMA overrun error09hDMA boundary error0ChUnknown media type10hCRC failed on floppy read20hController failure40hSeek failed80hTimeout42h–48hINT 13hFloppy disk controller status bytes and command bytes forthe hard disk controller.49hINT 10hCurrent video display mode setting.4Ah–4BhINT 10hNumber of text columns per line of current video mode.4Ch–4DhINT 10hCurrent page size in bytes.4Eh–4FhINT 10hOffset address of current display page, relative to the start ofvideo RAM. Video RAM starts at B800h in CGA andB000h in MDA.50h–5FhINT 10hCurrent cursor position for each video page. Up to eightdisplay pages are possible. Two bytes per page store thecurrent cursor position for each page. The MSB specifies therow (line) value and the LSB specifies the column value ofthe cursor. Change the cursor position using INT 10hfunctions. Do not change the values in this location.60hINT 10hStarting line of the cursor.61hINT 10hEnding line of the cursor.62hINT 10hCurrent video display page number.63h–64hINT 10hI/O port address of the video display adapter (the CRTcontroller address register). 3B4h for monochrome adapter.3D4h for color.65hINT 10hVideo display adapter mode register. The mode register isI/O port 3B8h for monochrome. 3D8h for CGA. 3D9h forEGA/VGA.66hINT 10hCurrent palette color.67h–6BhOption ROM address.6Ch–6FhINT 1AhCounter for INT 1Ah. Incremented by one every time INT08h occurs (18.2 times per second). Reset to 0 every 24hours.70hINT 1AhTimer 24-hour flag. 0 if the timer is between 0 and 24hours. Set to 1 when the time crosses 24 hours. Must bemanually reset.71hINT 16hBreak Key pressed flag.Bit 71<Ctrl><Break> or <Ctrl><C> pressed.72h–73hPOSTSoft reset flag. If 1234h, memory test is skipped on reboot.
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`14 AMIBIOS 98 Technical ReferenceOffsetBIOSService Description74h–77hINT 13hStatus of last hard disk drive operation.00hNo error01hInvalid function request02hAddress mark not found04hSector not found05hReset failed07hDrive parameter activity failed08hDMA overrun on operation09hData boundary error0AhBad sector flag selected0BhBad track detected0DhInvalid number of sectors on format0EhControl data address mark detected0FhDMA arbitration level out of range10hUncorrectable ECC or CRC error11hECC corrected data error20hGeneral controller failure40hSeek operation failed80hTimeoutAAhDrive not readyBBhUndefined error occurredCChWrite fault on selected driveE0hStatus error. Error register is 0FFhSense operation failed75h13hNumber of hard disk drives76h–77h13hHard disk drive work area78hINT 17hParallel port 1 timeout counter79hINT 17hParallel port 2 timeout counter7AhINT 17hParallel port 3 timeout counter7BhReserved7ChINT 14hSerial port 1 timeout counter7DhINT 14hSerial port 2 timeout counter7EhINT 14hSerial port 3 timeout counter7FhINT 14hSerial port 4 timeout counter80h–81hINT 16hStarting address of the keyboard buffer (usually 01Eh).82h–83hINT 16hEnding address of the keyboard buffer (usually 03Eh).84hINT 10hNumber of displayed character rows minus one.85h-86hINT 10hHeight of character matrix.
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`Chapter 3 BIOS Data Area 1515