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** Programmer's Technical Reference for MSDOS and the IBM PC ** USA copyright TXG 392-616 ALL RIGHTS RESERVED ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ DOSREF (tm) √ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ ISBN 1-878830-02-3 (disk-based text) Copyright (c) 1987, 1994 Dave Williams ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥ Shareware Version, 01/20/94 ≥ ≥ Please Register Your Copy ≥ ¿ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ C H A P T E R T W O CPU Port Assignments, System Memory Map, BIOS Data Area, Interrupts 00h to 09h C O N T E N T S Introduction ................................................... 2**1 System Memory Map .............................................. 2**2 A Brief Guide to Current Memory Terminology .................... 2**3 PC Port Assignment ............................................. 2**4 Reserved Memory Locations ...................................... 2**5 Absolute Addresses ............................................. 2**6 The IBM PC System Interrupts (Overview) ........................ 2**7 Quick Chart of Interrupts 00h-0FFh ............................. 2**8 IRQ Usage Chart ................................................ 2**9 The IBM-PC System Interrupts 00h-0Fh (in detail) ............... 2**10 Introduction ................................................... 2**1 For consistency in this reference, all locations and offsets are in hexadecimal unless otherwise specified. All hex numbers are prefaced with a leading zero if they begin with an alphabetic character, and are terminated with a lowercase H (h). The formats vary according to common usage. System Memory Map .............................................. 2**2 The IBM PC handles its address space in 64k segments, divided into 16k fractions and then further as necessary. ⁄ƒƒƒƒƒƒ¬ƒƒƒƒƒ¬ƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥start ≥start≥end ≥ ≥ ≥addr. ≥addr.≥addr.≥ usage ≥ ≥(dec) ≥ (hex) ≥ ≥ √ƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ *640k RAM Area* ≥ √ƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 0k ≥ ≥ start of RAM, first K is interrupt vector table ≥ ≥ 16k ≥0000-03FF≥ PC-0 system board RAM ends ≥ ≥ 32k ≥0400-07FF≥ ≥ ≥ 48k ≥0800-0BFF≥ ≥ √ƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 64k ≥1000-13FF≥ PC-1 system board RAM ends ≥ ≥ 80k ≥1400-17FF≥ ≥ ≥ 96k ≥1800-1BFF≥ ≥ ≥ 112k ≥1C00-1FFF≥ ≥ √ƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 128k ≥2000-23FF≥ ≥ ≥ 144k ≥2400-27FF≥ ≥ ≥ 160k ≥2800-2BFF≥ ≥ ≥ 176k ≥2C00-2FFF≥ ≥ √ƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 192k ≥3000-33FF≥ ≥ ≥ 208k ≥3400-37FF≥ ≥ ≥ 224k ≥3800-3BFF≥ ≥ ≥ 240k ≥3C00-3FFF≥ ≥ √ƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 256k ≥4000-43FF≥ PC-2 system board RAM ends ≥ ≥ 272k ≥4400-47FF≥ ≥ ≥ 288k ≥4800-4BFF≥ ≥ ≥ 304k ≥4C00-4FFF≥ ≥ √ƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 320k ≥5000-53FF≥ ≥ ≥ 336k ≥5400-57FF≥ ≥ ≥ 352k ≥5800-5BFF≥ ≥ ≥ 368k ≥5C00-5FFF≥ ≥ √ƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 384k ≥6000-63FF≥ ≥ ≥ 400k ≥6400-67FF≥ ≥ ≥ 416k ≥6800-6BFF≥ ≥ ≥ 432k ≥6C00-6FFF≥ ≥ √ƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 448k ≥7000-73FF≥ ≥ ≥ 464k ≥7400-77FF≥ ≥ ≥ 480k ≥7800-7BFF≥ ≥ ≥ 496k ≥7C00-7FFF≥ ≥ √ƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 512k ≥8000-83FF≥ ≥ ≥ 528k ≥8400-87FF≥ ≥ ≥ 544k ≥8800-8BFF≥ the original IBM PC-1 BIOS limited memory to ≥ ≥ 560k ≥8C00-8FFF≥ 544k ≥ √ƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 576k ≥9000-93FF≥ ≥ ≥ 592k ≥9400-97FF≥ ≥ ≥ 609k ≥9800-9BFF≥ ≥ ≥ 624k ≥9C00-9FFF≥ to 640k (top of RAM address space) ≥ ≥ 639k ≥ ≥ some RLL and SCSI hard disk adapters, some four ≥ ≥ ≥ ≥ floppy controller cards, some AMI and PS/2 BIOS, ≥ ≥ ≥ ≥ and assorted other cards sometimes try to use the≥ ≥ ≥ ≥ last K for storing temporary data. This can ≥ ≥ ≥ ≥ cause trouble with programs which assume they ≥ ≥ ≥ ≥ have a full 640k, and will prevent backfilling ≥ ≥ ≥ ≥ memory with some memory managers. Beware! ≥ √ƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥A0000 ***** 64k ***** EGA/VGA starting address ≥ ≥A0000 ***** 64k ***** Toshiba 1000 DOS ROM (MS-DOS 2.11V) ≥ √ƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 640k ≥A0000-A95B0≥ MCGA 320x200 256 color video buffer ≥ ≥ ≥ -AF8C0≥ MCGA 640x480 2 color video buffer ≥ ≥ ≥ -A3FFF≥ ≥ ≥ 656k ≥A4000-A7FFF≥ ≥ ≥ 672k ≥A8000-ABFFF≥this 64k segment may be used for contiguous DOS ≥ ≥ 688k ≥AC000-AFFFF≥RAM with appropriate hardware and software ≥ √ƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥B0000 ***** 64k ***** mono and CGA address ≥ √ƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 704k ≥B0000-B3FFF≥4k mono display | The PCjr and early Tandy 1000≥ ≥ 720k ≥B4000-B7FFF≥ | BIOS revector direct write to≥ ≥ 736k ≥B8000-BBFFF≥16k CGA | the B8 area to the Video Gate≥ ≥ 756k ≥BC000-BFFFF≥ | Array and reserved system RAM≥ √ƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥C0000 ***** 64k *************** expansion ROM ≥ √ƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 768k ≥C0000-C3FFF≥16k EGA BIOS C000:001E EGA BIOS signature ≥ ≥ ≥ ≥ (the letters 'IBM') ≥ ≥ ≥C0000-C7FFF≥32k VGA BIOS extension (typical) ≥ ≥ 784k ≥C4000-C5FFF≥ ≥ ≥ ≥C6000-C63FF≥256 bytes IBM PGC video communications area ≥ ≥ ≥C6400-C7FFF≥ ≥ ≥ 800k ≥C8000-CBFFF≥16k hard disk controller BIOS, drive 0 default ≥ ≥ ≥CA000 ≥ some 2nd floppy (HD) controller BIOSes ≥ ≥ 816k ≥CC000-CDFFF≥ 8k IBM PC Network NETBIOS ≥ ≥ ≥CE000-CFFFF≥ ≥ √ƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥D0000 ***** 64k ***** expansion ROM ≥ √ƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 832k ≥D0000-D7FFF≥32k IBM Cluster Adapter | PCjr first ROM cart. ≥ ≥ ≥ DA000≥voice communications | address area. ≥ ≥ 848k ≥D4000-D7FFF≥ | Common EMS board ≥ ≥ 864k ≥D8000-DBFFF≥ | paging area. ≥ ≥ ≥D8000-DBFFF≥ IBM Token Ring default Share RAM address ≥ ≥ ≥DC000 ≥ IBM Token Ring default BIOS/MMIO address ≥ ≥ 880k ≥DC000-DFFFF≥ | ≥ ≥ ≥DE000 ≥4k TI Pro default video buffer ≥ √ƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥E0000 ***** 64k ***** expansion ROM ≥ ≥ wired to ROM sockets in the original IBM AT ≥ ≥ used by ABIOS extensions on some PS/2 models ≥ √ƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 896k ≥E0000-E3FFF≥ | PCjr second ROM cart.≥ ≥ 912k ≥E4000-E7FFF≥ | address area ≥ ≥ 928k ≥E8000-EBFFF≥ | ≥ ≥ 944k ≥EC000-EFFFF≥ | spare ROM sockets on ≥ ≥ ≥ ≥ | IBM AT (reserved in ≥ ≥ ≥ ≥ | hardware) ≥ √ƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥F0000 ***** 64k ***** system ≥ √ƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 960k ≥F0000-F3FFF≥reserved by IBM | cartridge address ≥ ≥ 976k ≥F4000- ≥ | area (PCjr cartridge ≥ ≥ ≥F6000 ≥ROM BASIC Begins | BASIC) ≥ ≥ 992k ≥F8000-FB000≥ | ≥ ≥ 1008k≥FC000-FFFFF≥ROM BASIC and original | ≥ ≥ ≥ ≥BIOS (Compatibility BIOS | ≥ ≥ ≥ ≥in PS/2) | ≥ ≥ 1024k≥ FFFFF≥end of memory (1024k) for 8088 machines ≥ √ƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒ¡ƒ¬ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 384k ≥100000-15FFFF≥ 80286/AT extended memory area, 1Mb mbd. ≥ ≥ 15Mb ≥100000-FFFFFF≥ 80286/AT extended memory address space ≥ ≥ 15Mb ≥160000-FDFFFF≥ Micro Channel RAM expansion (15Mb ext. mem) ≥ ≥ 128k ≥FE0000-FFFFFF≥ system board ROM (PS/2 Advanced BIOS) ≥ √ƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒ¡ƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 64k ≥C0000000-C000FFFF≥ Weitek "Abacus" math coprocessor ≥ ≥ ≥ ≥ memory-mapped I/O ≥ ¿ƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ 1) Note that the ROM BIOS has a duplicated address space which causes it to "appear" both at the end of the 1 megabyte real mode space and at the end of the 16 megabyte protected mode space. The addresses from 0E0000 to 0FFFFF are equal to 0FE0000 to 0FFFFFF. This is necessary due to differences in the memory addressing between Real and Protected Modes. 2) Late IBM XTs and ATs with support for the 101-key keyboards ran out of ROM space at the top of their ROM blocks. These machines "wrap around" and jump to an address lower than their original entry point to store their code. ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø 1024k ≥ top of memory ≥ √ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ 976k ≥ original BIOS area ≥ ƒƒƒƒø √ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ ≥ extended BIOS area ≥ <ƒƒŸ √ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ 3) IBM PS/2s reserve the last K of memory before A000 for a scratch area for the ABIOS ROM routines. This limits PS/2 machines to 639k. Apparently only 10 to 20 bytes of memory is actually used; though there was room for that much down in unused portions of the BIOS Data Area, IBM evidently decided to leave room to grow. Sometimes other stuff can use the last K. OMTI hard disk controllers' firmware wanted the last K, as do some XTs with ROM- based disk caches. These don't like to coexist at all. SpeedStor (disk management software) has a program called OMTIfix bundled to allow it to work with these controllers. A few extended-VGA ANSI drivers also grab the last K. QEMM, 386Max, and other memory managers can relocate this memory to give a complete 640k. 4) When running with a 286 and memory manager board or on a 386, PC- MOS/386 relocates its kernel to the 0C000-0F000 high memory area to leave more of the lower 640k for applications. 0A000-0BFFFF is reserved for swapping video RAM as it becomes active. MOS supports monochrome and CGA modes directly. 5) Most AT compatible machines use the entire Fxxx block for BIOS. PS/2 and PS/2 compatible machines take an entire 128k from E000- FFFF. Most real IBM machines also have the BASIC ROMs taking up some of the high address space. A Brief Guide to Current Memory Terminology .................... 2**3 LOW MEMORY - 0000h to around 0:5(something), comprising the 80x8x interrupt vector table, the BIOS Data Area, DOS Data Area, etc. CONVENTIONAL MEMORY - from the end of low memory to the beginning of the "reserved by IBM" A000 segment (640k). HIGH MEMORY - originally noncontiguous RAM stuffed into the "reserved for ROM expansion" areas, typically segments D000 and E000. DOS normally can't access this memory without a driver of some sort, but it's easy to put RAMdisks and stuff in there. HIGH DOS MEMORY - same as above. CONVENTIONAL MEMORY - extra RAM stuck at A000, assuming the machine already has 640k, appears as conventional memory accessible to DOS and applications. IBM clones can typically add 64k before bumping into a mono card or 96k before hitting a color card. This address is part of the EGA/VGA video RAM area and most EGA cards don't like system memory at A000. With semi-compatible machines like the IBM PCjr or Sanyo 55x, it was possible to get as much as 960k of real, usable DOS conventional memory, since they used a different video system and had no hard disk ROM to break up the space between 640k and the beginning of the ROM BIOS. EXPANDED MEMORY - LIM 3.2, LIM 4.0, or EEMS 3.2 bank switched memory. A RAM "window" allows an application to save a block of RAM to an expansion board. The window size and location varies according to the EMS standard being used. EXTENDED MEMORY - this is the "native mode" address space of the 80286 and later chips. The "real mode", or 8088 addressing scheme, sees RAM as a collection of segments and offsets with a limit on segment size. "Protected mode" addressing uses a flat linear addressing scheme. 8088 and 80188 chips do not have extended memory. HIGH MEMORY - by fiddling a bit with the segment/offset stuff, you can get an extra block of addressable 8088-mode memory just over the 1 meg address space when using 80286 and later microprocessors. Microsoft issued their "HMA" (High Memory Area) standard to try to standardize use of this block. Though it really is "high" memory, "high" had for many years referred to memory between 640k and 1mb. This creates more confusion for new programmers. EMS - this is expanded memory as described above XMS - Microsoft is pushing an "Extended Memory Standard" which defines a page-switching scheme much like EMS. The only real difference is that XMS uses protected-mode RAM instead of a special paged RAM board. XMS - some severely brain-damaged jerk at IBM issued documentation for some IBM *EMS* boards referring to the boards as *XMS*. This was a classic blunder, and now some IBM-followers are picking up the aberrant terminology. This is guaranteed to confuse some people. To make it simple, if it needs an expansion board, it is EMS no matter what the vendor calls it. UMB - Upper Memory Blocks. These are defined in the Microsoft XMS Specification. Unfortunately, some people have begun using "UMB" to refer to the HMA and High DOS areas indiscriminately. PC Port Assignment ............................................. 2**4 The Intel 80x86 processors have a 64K I/O memory space for addressing external devices. The 8088 through 80286 processors can divide their I/O space into either 8 bit or 16 bit ports. The 386 and later can have 8, 16, or 32 bit ports. Some port addresses are mapped to the motherboard, others to the slots. The XT's boundary was at 200h, while the AT and EISA is at 100h. Many cards avoid the 100h-200h zone for XT compatibility. These are functions common across the IBM range. The PCjr, PC-AT, PC Convertible and PS/2 (both buses) have enhancements. In some cases, the AT and PS/2 series ignore, duplicate, or reassign ports arbitrarily. If your code incorporates specific port addresses for video or system board control it would be wise to have your application determine the machine type and video adapter and address the ports as required. hex address Function Models PCjr|PC|XT|AT|CVT|M30|PS2 0000-000F 8237 DMA controller PC------------------ 0000-001F 8237 DMA controller 1 -----AT---------PS2 0020-0027 8259A interrupt controller ------------------- 0020-002F IOSGA interrupt function ----------------PS2 0020-003F 8259A interrupt controller (AT) ------------------- 0020-0021 interrupt controller 1, 8259A PC----AT---------PS2 0040-0043 programmable timer 8253 PC------------------ 0040-0047 programmable timers ----------------PS2 0040-005F 8253-5 programmable timers -----AT------------ note 1) 0041 was memory refresh in PCs. Not used in PS/2. 2) A few early 80386 machines used static RAM and did not use refresh at all. The PCjr refreshes by the video vertical retrace signal. 0040 8254 programmable interval timer 1 system clock (counter 0) 0041 8254 timer 1 refresh request (counter 1) 0042 8254 timer 1 speaker tone (counter 2) ------------------- 0043 8254 timer 1 command register ------------------- 0049 8254 timer 2 not used (counter 1) ------------------- 004A programmable interval timer 2 ------------------- 004B programmable interval timer 2 ------------------- 0060-0063 keyboard controller 8255A PC----------------- 0060-006F 8042 keyboard controller -----AT------------ 0060 8042 data I/O register ------------------- 0060 IOSGA keyboard input port ----------------PS2 0061 speaker PCjr PC-XT-AT-CVT-------- 0061 IOSGA speaker control ------------M30-PS2 0061 On some clones, setting or clearing bit 2 controls Turbo mode 0061 Toshiba 1000 - system command ------------------- 0062 IOSGA configuration control ------------M30-PS2 0062 Toshiba 1000 - System Status, port C ------------------- 0063 SSGA, undocumented ----------------PS2 0063 Toshiba 1000 - mode set ------------------- 0064 keyboard auxiliary device ----------------PS2 0064 keyboard 8042 status register -----AT------------ 0065 AT&T 6300+ high/low chip select ------------------- 0065-006A SSGA, undocumented ----------------PS2 0066 AT&T 6300+ system configuration switch 2 0067 AT&T 6300+ system configuration switch 1 0068 C&T chipsets, turbo mode ------------------- 006B SSGA, RAM enable/remap ----------------PS2 006C-006F SSGA, undocumented ----------------PS2 0070 AT CMOS write internal register ------------------- 0071 AT CMOS read internal register ------------------- 0070-0071 CMOS real-time clock, NMI mask ----------------PS2 0070-007F CMOS real-time clock, NMI mask -----AT, AT&T 6300+ 0074-0076 reserved ----------------PS2 0080-0083 AT&T 6300+ DMA page registers (8 bit) ------------------- 0080-008F SSGA DMA page registers ----------------PS2 0080-009F DMA page registers, 74LS612 -----AT------------ Channel 2 = 0081 Channel 3 = 0082 Channel 1 = 0083 Channel 0 = 0087 Channel 6 = 0089 Channel 5 = 008B 0090 central arbitration control port (Micro Channel) 0091 card selected feedback (Micro Channel) 0092 system control port A (Micro Channel) 0092 Fast Gate A20, some C&T chipsets, Micronics motherboards 0093 reserved (Micro Channel) 0094 system board setup (Micro Channel) 0096 POS "CD SETUP" selector (Micro Channel) 00A0-00A1 Interrupt controller 2, 8259A -----AT---------PS2 00A0-00A3 AT&T 6300+, NMI register ------------------- 00A0-00AF IOSGA NMI mask register ----------------PS2 00B0-00BF realtime clock/calendar, (undocumented) --------------PS2 00C0-00C3 AT&T 6300+, reserved ------------------- 00C0-00CF DOS ROM register, Toshiba 1000 ------------------- 00C0-00CF 8237A-5 word DMA controller 00C0-00DF reserved PCjr PC XT AT CVT M30 00D0-00D3 AT&T 6300+, reserved ------------------- 00D0-00EF "special" register, Toshiba 1000 ------------------- 00C0 0C1 key register, Toshiba 1000 ------------------- 00C1 keyboard transfer register, Toshiba 1000 00C2 keyboard receive register, Toshiba 1000 00C3 keyboard status register, Toshiba 1000------------------- 00C8 DOS ROM page register, Toshiba 1000 ------------------- 00E0 CPU speed control, Toshiba 1000 ------------------- 00E1 keyboard status/0E2 key register, Toshiba 1000 00E2 work register, Toshiba 1000 ------------------- 00E3 0E4 key register, Toshiba 1000 ------------------- 00E4 system control register 0, Toshiba 1000 00E4 Weitek ABACUS NDP - bit 0=1, ABACUS is present 00E5 0E6 key register, Toshiba 1000 ------------------- 00E6 system control register 1, Toshiba 1000 00EE EMS unit index, Toshiba 1000 ------------------- 00EF EMS unit data, Toshiba 1000 ------------------- 00C0-00DF DMA controller 2, 8237A-5 -----AT---------PS2 00E0-00EF realtime clock/calendar (undocumented)-----------M30 PS2 00E0-00FF AT&T 6300+, 80287 ------------------- 00F0-00FF PS/2 math coprocessor I/O (Model 50+) (diskette IO on PCjr) 00F0 clear math coprocessor busy ------------------- 00F1 reset math coprocessor ------------------- 00F8-00FF AT 80287/80387 coprocessor control ------------------- 0100-0101 PS/2 POS adapter ID response (Micro Channel) 0100-010F Always IN-2000 alternate 2 ------------------- 0100-02F7 AT&T 6300+, reserved ------------------- 0102-0107 PS/2 POS adapter configuration response (Micro Channel) 0110-011F Always IN-2000 alternate 2 ------------------- 0150 Geographics Drafting Board digitizer ------------------- 0180 Stargate Plus 8 multiport serial board------------------- 01F0-01F8 hard disk -----AT---------PS2 0200-0201 game-control adapter (joystick) ------------------- 0200-0207 Sound Blaster joystick port ------------------- 0200-020F game controller PC---AT------------ 0200-020F Always IN-2000 alternate 1 0208-0209 Chips & Technology CS8221 chipset default EMS ports alternate addresses: 218h, 258h, 268h, 2A8h, 2B8h, 2E8h 0208-020F Toshiba 1000 - EMS unit I/O #1 ------------------- 020C-020D reserved by IBM ------------------- 0210-0217 IBM expansion chassis (PC, XT) ------------------- 0218-021F Toshiba 1000 - EMS unit I/O #2 ------------------- 021F reserved by IBM ------------------- 0220 LANtastic 2mbps adapter optional ------------------- 0220 Sound Blaster 1-6 data port opt 1 ------------------- 0221 Sound Blaster 1-6 register port opt 1 ------------------- 0222 Sound Blaster 7-12 data port opt 1 ------------------- 0223 Sound Blaster 7-12 register port opt 1------------------- (opt 1:220h, opt 2:210h, opt 3:230h, opt 4: 240h, opt 5:250h, opt 5:260h, FM music and DSP ports also adjustable) 0220-022F Always IN-2000 SCSI adapter default addresses 0220 IRMA 3270 terminal emulator command port 0221 IRMA 3270 terminal emulator data port 1 0222 IRMA 3270 terminal emulator data port 2 0223 IRMA 3270 terminal emulator data port 3 0224 IRMA 3270 terminal emulator reserved for future use 0225 IRMA 3270 terminal emulator reserved for future use 0226 IRMA 3270 terminal emulator Command Request flag 0226 Sound Blaster DSP Reset ------------------- 0227 IRMA 3270 terminal emulator Attention Request flag 0228 Sound Blaster FM music data/status port 0229 Sound Blaster FM music register port ------------------- 022A Sound Blaster DSP (voice I/O and MIDI) Read Data 022C Sound Blaster DSP Write Data or Command 022C Sound Blaster DSP Write Buffer Status (bit 7) 022C Marstek scanner adapter, optional ------------------- 022E Sound Blaster DSP Data Available (bit 7) 0232-023E Microsoft bus & InPort mouse cards (default address) 0238-023C Microsoft bus & InPort mouse cards (optional address) 023C-023F Logitech bus mouse ------------------- 0240 LANtastic 2mbps adapter optional ------------------- 0240-0247 Corvus Omninet NIC opt 1 ------------------- 0248-024F Corvus Omninet NIC opt 2 ------------------- 0250-0257 Corvus Omninet NIC opt 3 ------------------- 0258-0259 LIM EMS 3.1 (not defined in 3.2+) ------------------- 0258-025F Corvus Omninet NIC opt 4 ------------------- 0258-025F Toshiba 1000 - EMS unit I/O #3 ------------------- 0260 LANtastic 2mbps adapter optional ------------------- 0268 CompuCom internal modem, COM20, COM21, COM22 026C Marstek scanner adapter, optional ------------------- 0268-026F Toshiba 1000 - EMS unit I/O #4 ------------------- 0268-026F Copy II PC Option Board, default ------------------- 0278 CompuCom internal modem, COM6, COM8, COM13 0278-027F parallel printer port 2 -----AT------------ 0278-027B parallel printer port 3 ----------------PS2 0280-0281 Frecom FAX96 board default ------------------- 0280-0284 NetWorth Engineering vLAN V2.1 NIC opt 1 0280 LANtastic 2mbps adapter optional ------------------- 0280 Logitech ScanMan, default ------------------- 0280 Needham Electronics PB-10 EPROM burner, optional 0288-0289 Frecom FAX96 board alternate 1 ------------------- 0290 Needham Electronics PB-10 EPROM burner, optional 02A0 Logitech ScanMan, option 1 ------------------- 02A0-02BF Gateway G-Net NIC opt 1 ------------------- 02A0 LANtastic 2mbps adapter optional ------------------- 02A2 clock chip in early Sperry PCs ------------------- 02A8-02AF Toshiba 1000 - EMS unit I/O #5 ------------------- 02AC Marstek scanner adapter, optional ------------------- 02B0-02DF EGA (alternate) PC---AT------------ 02B8-02BF Toshiba 1000 - EMS unit I/O #6 ------------------- 02B8-02B9 Novell Star Intelligent NIC opt 1 ------------------- 02B8-02BB Novell Standard NIC ------------------- 02BC-02BD Novell Star Intelligent NIC opt 2 ------------------- 02C0-02DF Toshiba 1000 - realtime clock ------------------- 02C0-02C7 AST SixPackPlus clock ------------------- 02E0-02EF Gateway G-Net NIC opt 2 ------------------- 02E0-02EF Allen-Bradley VistaLAN/PC adapter, optional address 1 02E0-02EF Standard Microsystems ARCNET NIC opt 1------------------- 02E0 Stac Electronics AT/16 compression board (Stacker) 02E0 this is a common address for generic Arcnet cards 02E1 GPIB (adapter 0) -----AT------------ 02E2-02E3 data acquisition (adapter 0) -----AT------------ 02E8 "industry standard" COM4 ------------------- 03E8 CompuCom internal modem, COM17, COM18, COM19 02E8-02EF Toshiba 1000 - EMS unit I/O #7 ------------------- 02E8-02EF Copy II PC Option board, optional 1 ------------------- 02EC most Marstek scanner boards, default ------------------- 02F0-02FF Standard Microsystems ARCNET NIC opt 2------------------- 02F8-02FF serial communications (COM2) PC---AT---------PS2 0300 Periscope debugger card ------------------- 0300-0307 Pelican 5.5mb floppy adapter, default address 0300-030F Standard Microsystems ARCNET NIC opt 3------------------- 0300-030F 3Com EtherLink NIC opt 1 ------------------- 0300-031F Gateway G-Net NIC opt 3 ------------------- 0300-031F prototype card PC---AT------------ 0300-031F Leading Edge Model D clock ------------------- 0300 some Samsung XT clock/calendar on motherboard 0300 Needham Electronics PB-10 EPROM burner, default 0300-0303 Tecmar/Wangtek PC-36 tape controller board, default 0300-0307 3Com 3C505 EtherLink Plus NIC opt 1 ------------------- 0300-0307 Proteon ProNET NIC w/checksum opt 1 ------------------- 0308-030F Proteon ProNET NIC w/checksum opt 2 ------------------- 0300-031F Torus Ethernet adapter, optional address 1 0300-031F Micom-Interlan N15010 Ethernet NIC opt 1 0300-031F Cabletron Ethernet E-1010 NIC ------------------- 0310-0317 3Com 3C505 EtherLink Plus NIC opt 1 ------------------- 0310-0317 Proteon ProNET NIC w/checksum opt 3 ------------------- 0310-0317 Pelican 5.5mb floppy adapter, optional address 1 0310-031F 3Com EtherLink NIC opt 2 ------------------- 0320 LANtastic 2mbps adapter optional ------------------- 0320 Perstor HD controller, primary addr ------------------- 0320 many CD-ROM proprietary adapters, default address 0320-0323 AT&T 6300+, hard disk controller ------------------- 0320-0327 3Com 3C505 EtherLink Plus NIC opt 1 ------------------- 0320-032F hard disk controller PC----------------- 0320-033F Torus Ethernet adapter, optional address 2 0320-033F Micom-Interlan N15010 Ethernet NIC opt 1 0324 Perstor PS180 HD ctrlr, 2ndary addr ------------------- 0324-0327 C: common secondary hard disk controller address 032C Marstek scanner adapter, optional ------------------- 0330 Logitech ScanMan, option 2 ------------------- 0338-033B Tecmar PC-36 tape controller board, option 1 0340 LANtastic 2mbps adapter optional ------------------- 0340 Logitech ScanMan, option 3 ------------------- 0340 Sony CD-ROM adapters ------------------- 0340 Severn (Sony) CD-ROM adapters ------------------- 0340-0347 Proteon ProNET NIC w/checksum opt 4 ------------------- 0340-0347 Novell Disk Coprocessor #1 ------------------- 0348-034F Novell Disk Coprocessor #2 ------------------- 0348-0357 DCA 3278 emulator ------------------- 0358-0359 Novell Star Intelligent NIC opt 3 ------------------- 035C-035D Novell Star Intelligent NIC opt 4 ------------------- 0360 LANtastic 2mbps adapter optional ------------------- 0360-0367 PC Network (low address) ------------------- 0360-0367 AT&T StarLAN NIC opt 1 ------------------- 0360-0367 Ungermann-Bass Net/One Personal Connection NIC 0368 CompuCom internal modem, COM7, COM11, COM12 0368-036B Tecmar PC-36 tape controller board, option 2 036C Marstek scanner adapter, optional 0368-036F PC Network (high address) -----AT------------ 0368-036F AT&T StarLAN NIC opt 2 ------------------- 0368-036F Ungermann-Bass Net/One Personal Connection NIC 0368-036F Torus Ethernet adapter, optional address 3 0368-036F Copy II PC Option Board, optional 2 ------------------- 0370 Colorado Memory external tape backup control port ------- Archive external tape backup control port --------------- 0370-0377 some "second controller" floppy cards ------------------- 0372 Systen OmniBridge floppy card, alternate address 1 0378 CompuCom internal modem, COM5, COM9, COM10 0378-037F parallel printer port PC---AT------------ 0378-037B parallel printer port ----------------PS2 0380-0387 PCNet NIC, Orchid, Santa Clara, AST ------------------- 0380-0387 Pelican 5.5mb floppy adapter, optional address 2 -------- 0380-0381 Frecom FAX96 board alternate 2 ------------------- 0380-0384 NetWorth Engineering vLAN V2.1 NIC opt 1 0380-038F Eicon Technology Network Adapter (X.25) board (default) 0380-038F SDLC, bi-synchronous 2 PC---AT------------ 0380-0389 BSC communications (alternate) PC----------------- 0388-0389 Frecom FAX96 board alternate 3 ------------------- 0388-0389 Sound Blaster FM music, alternate 2 ------------------- 0390 Needham Electronics PB-10 EPROM burner, optional 0390-0397 Pelican 5.5mb floppy adapter, optional address 3 -------- 0390-039F Eicon Technology Network Adapter (X.25) board (alternate) 0390-0393 cluster (adapter 0) PC---AT------------ 0398-039B Tecmar PC-36 tape controller board, option 3 03A0-03A9 BSC communications (primary) PC---AT------------ 03AC Marstek scanner adapter, optional ------------------- 03B0-03BF monochrome/parallel printer adapter PC---AT------------ 03B4-03B5 video subsystem ----------------PS2 03B4-03BF Hercules Mono Card ------------------- 03BA video subsystem ----------------PS2 03BC-03BF parallel printer port 1 ----------------PS2 03C0-03CF Enhanced Graphics Adapter ------------------- 03C0-03DA video subsystem and DAC ----------------PS2 03C8-03CB Tecmar PC-36 tape controller board, option 4 03DA video status register AT&T 6300, Olivetti PC 03D0-03DF CGA, MCGA, VGA adapter control ------------------- 03DE video mode selector register AT&T 6300, Olivetti PC 03E0-03EF Allen-Bradley VistaLAN/PC adapter, optional address 1 03E8h "industry standard" COM3 ------------------- 03E8 CompuCom internal modem, COM14, COM15, COM16 03E8-03EF Copy II PC Option Board, optional 3 ------------------- 03F0-03F7 floppy disk controller PC---AT---------PS2 03F0 Colorado Memory internal tape backup control port ------- 03F2 DTK high-density XT floppy controller (output only) 03F2 Systen OmniBridge floppy card, alternate address 2 03F5 DTK high-density XT floppy controller PC-XT-------------- 03FC Marstek scanner adapter, optional ------------------- 03F8-03FF serial communications (COM1) PC---AT---------PS2 0400-3FFF AT&T 6300+, unused ------------------- 06E2-06E3 data acquisition (adapter 1) -----AT------------ 0790-0793 cluster (adapter 1) PC---AT------------ 0878 Compaq 386SX VGA BIOS relocation -----AT------------ 0920 C&T/Micronics Fast Gate A20 ------------------- 0A20-0A23 IBM Token Ring opt 1 ------------------- 0A24-0A27 IBM Token Ring opt 2 ------------------- 0AE2-0AE3 data acquisition (adapter 2) -----AT------------ 0B90-0B93 cluster (adapter 2) PC---AT------------ OC80-0C83 EISA Product Identifier access port ------------------- 2 bytes 3 letters (compressed) abbreviated manufacturer ID. The letters "ISA" are reserved for old bus boards. 1 byte 2-digit product number 1 byte 2-digit revision number (mfr. abbreviations are assigned by BCPR Services, the group that distributes the EISA specification) 0EE2-0EE3 data acquisition (adapter 3) -----AT------------ 1390-1393 cluster (adapter 3) PC---AT------------ 2160 IBM XGA adapter (not motherboard) (only 1 installed) 22E1 GPIB (adapter 1) ------------------- 2390-2393 cluster (adapter 4) PC---AT------------ 3F00-3F1F AT&T 6300+, -RESET CS ------------------- 3F20-3F3F AT&T 6300+, -PROTECTEN ------------------- 3F40-3F5F AT&T 6300+, -TIME SLICEN ------------------- 3F60-3F7F AT&T 6300+, -TRAPCE ------------------- 3F80-3F9F AT&T 6300+, -VXLATEN ------------------- 3FA0-3FBF AT&T 6300+, -BITREAD ------------------- 3FC0-3FDF AT&T 6300+, -ADADV ------------------- 3FE0-3FFF AT&T 6300+, -CLear TRAP address ------------------- 4258 LIM EMS 3.1 (not defined in 3.2+) ------------------- 42E1 GPIB (adapter 2) -----AT------------ 62E1 GPIB (adapter 3) -----AT------------ 8258 LIM EMS 3.1 (not defined in 3.2+) ------------------- 82E1 GPIB (adapter 4) -----AT------------ A2E1 GPIB (adapter 5) -----AT------------ C258 LIM EMS 3.1 (not defined in 3.2+) ------------------- C2E1 GPIB (adapter 6) -----AT------------ E2E1 GPIB (adapter 7) -----AT------------ note 1) IOSGA = I/O Support Gate Array SSGA = System Support Gate Array 2) I/O Addresses, hex 000 to 0FF, are reserved for the system board I/O. Hex 100 to 3FF are available on the I/O channel. 3) These are the addresses decoded by the current set of adapter cards. IBM may use any of the unlisted addresses in the future. 4) SDLC Communication and Secondary Binary Synchronous Communications cannot be used together because their port addresses overlap. Reserved Memory Locations ...................................... 2**5 ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ ≥ 000-3FF - 1k DOS interrupt vector table, 4 byte vectors for ≥ interrupts 00h-0FFh. ≥ 30:00 - used as a stack area during POST and bootstrap routines. ≥to 3F:FF This stack area may be revectored by user applications √ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ ≥ ** The BIOS Data Area ** addresses from 400h to 4FFh √ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ ≥addr.≥ size ≥ description √ƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ ≥40:00≥ word ≥ COM1 port addr. | These addresses are zeroed out in the ≥40:02≥ word ≥ COM2 port addr. | OS/2 DOS Compatibility Box if any of ≥40:04≥ word ≥ COM3 port addr. | the OS/2 COMxx.SYS drivers are loaded. ≥40:06≥ word ≥ COM4 port addr. | | note: no value for COM2 was set in ≥40:08≥ word ≥ LPT1 port addr. | early IBM PS/2 Model 50Zs. ≥40:0A≥ word ≥ LPT2 port addr. | DESQview sets 40:00-40:02 to zero ≥40:0C≥ word ≥ LPT3 port addr. | if a program is swappable ≥40:0E≥ word ≥ LPT4 port addr. (not valid in PS/2 machines) ≥40:0E≥ word ≥ PS/2 pointer to 1k extended BIOS Data Area at top of ≥40:10≥ word ≥ RAM equipment flag (see int 11h) ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ bits: ≥ 0 0 no floppy drive present ≥ 1 if floppy drive present (see bits 6&7) ≥ 1 0 no math coprocessor installed ≥ 1 if 80x87 installed (not valid in PCjr) ≥ 2,3 system board RAM (not used on AT or PS/2) ≥ 0,0 16k 0,1 32k ≥ 1,0 48k 1,1 64k ≥ 4,5 initial video mode ≥ 0,0 no video adapter ≥ 0,1 40 column color (PCjr default) ≥ 1,0 80 column color ≥ 1,1 MDA ≥ 6,7 number of diskette drives ≥ 0,0 1 drive 0,1 2 drives ≥ 1,0 3 drives 1,1 4 drives ≥ 8 0 DMA present ≥ 1 DMA not present (PCjr, Tandy 1400, ≥ Sanyo 55x) ≥ 9,A,B number of RS232 serial ports ≥ C game adapter (joystick) ≥ 0 no game adapter ≥ 1 if game adapter ≥ D serial printer (PCjr only) ≥ 0 no printer ≥ 1 serial printer present ⁄ƒƒƒƒƒƒŸ E,F number of parallel printers installed ≥note 1) The IBM PC and AT store the settings of the system board ¿ƒƒƒø switches or CMOS RAM setup information (as obtained by ≥ the BIOS in the Power-On Self Test (POST)) at addresses ≥ 40:10h and 40:13h. 00000001b indicates "on", 00000000b ≥ is "off". ≥ 2) DOS only uses 40:10 when it's booting to find out how ≥ many drives it has. XT BIOSes use 40:10 to find out how ≥ many drives they support, but AT BIOSes don't seem to - ≥ they use the state bytes at 40:90/91 instead. ⁄ƒƒƒƒƒ¬ƒƒƒƒ¡ƒƒø ≥40:12≥ byte ≥ reserved (PC, AT) ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ number of errors detected by infrared keyboard link ≥ (PCjr) manufacturer test (Phoenix BIOS) ≥ bits 7-1 reserved ≥ bit 0 0 non-test mode ≥ 1 manufacturing test mode ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ POST status (Convertible) ≥40:13≥ word ≥ available memory size in Kbytes, less display RAM in ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ PCjr, or Extended BIOS Data Area (40:0E) if used. This ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ is the value returned by int 12h. ≥40:15≥ word ≥ reserved ≥40:17≥ byte ≥ keyboard flag byte 0 (see int 9h) ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ bit 7 insert mode on 3 alt pressed ≥ 6 capslock on 2 ctrl pressed ≥ 5 numlock on 1 left shift pressed ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 4 scrollock on 0 right shift pressed ≥40:18≥ byte ≥ keyboard flag byte 1 (see int 9h) (IBM, old style) ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ bits 0=not pressed, 1=pressed ≥ bit 7 insert pressed 3 ctrl-numlock (pause) toggled ≥ 6 capslock pressed 2 PCjr keyboard click active ≥ 5 numlock pressed 1 PCjr ctrl-alt-capslock held ≥ 4 scrollock pressed 0 ≥ ≥ keyboard flag byte 1 (see int 9h) (IBM, Phoenix, new style) ≥ bit 7 insert pressed 3 ctrl-numlock (pause) toggled ≥ 6 capslock pressed 2 SysReq pressed (enhanced kbd) ≥ 5 numlock pressed 1 Left alt pressed (enhanced kbd) ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 4 scrollock pressed 0 Right alt pressed (enhanced kbd) ≥40:19≥ byte ≥ storage for alternate keypad entry (not normally used) ≥ ≥ ≥ Phoenix says, "Work area for Alt key and numeric keypad ≥ ≥ ≥ input" ≥40:1A≥ word ≥ pointer to keyboard buffer head character ≥40:1C≥ word ≥ pointer to keyboard buffer tail character ≥40:1E≥32bytes≥ 16 2-byte entries for keyboard circular buffer, read by ≥ ≥ ≥ int 16h a maximum of 15 entries are used at one time ≥40:3E≥ byte ≥ drive seek status - if bit=0, next seek will recalibrate ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ by repositioning to Track 0. ≥ bit 7 disk hdw int occured 5 not used ≥ 6 not used 4 not used ≥ 3 drive D bit 2 drive C ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 1 drive B 0 drive A ≥40:3F≥ byte ≥ diskette motor status (bit set to indicate condition) ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ bit 7 0 current operation is a read or verify ≥ 1 current operation is a write or format ≥ 6 reserved ≥ 5,4 drive select states, where: ≥ 00 drive 0 selected ≥ 01 drive 1 selected ≥ 10 drive 2 selected ≥ 11 drive 3 selected ≥ 3 1 motor on (drive 3) ≥ 2 1 motor on (drive 2) ≥ 1 1 motor on (drive 1) ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 0 1 motor on (drive 0) ≥40:40≥ byte ≥ motor off counter ≥ ≥ ≥ starts at 37 and is decremented 1 by each system clock ≥ ≥ ≥ tick. Motor is shut off when count = 0. ≥40:41≥ byte ≥ status of last diskette operation where: ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ (IBM XT) ≥ bit 7 timeout failure 3 DMA overrun ≥ 6 seek failure 2 sector not found ≥ 5 controller failure 1 address not found ≥ 4 CRC failure 0 bad command ≥ (Phoenix) ≥ bit 7 1 drive not ready ≥ 6 1 seek failure ≥ 5 1 controller failure ≥ 4,0 error codes in hex, where: ≥ 01h illegal function request ≥ 02h address mark not found ≥ 03h write protect error ≥ 04h sector not found ≥ 06h diskette change line active ≥ (AT & later) ≥ 08h DMA overrun ≥ 09h 64K DMA boundary error ≥ 0Ch media type not found ≥ 10h uncorrectable EEC or CRC error ≥ 20h general controller failure ≥ 40h seek operation failed ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 80h timeout ≥40:42≥7 bytes≥ NEC floppy controller chip status bytes (see Chapter 15) ≥40:49≥ byte ≥ Video Control Data Area 1 ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ current CRT mode (hex value) ≥ 00h 40x25 BW (CGA) 01h 40x25 color (CGA) ≥ 02h 80x25 BW (CGA) 03h 80x25 color (CGA) ≥ 04h 320x200 color (CGA) 05h 320x200 BW (CGA) ≥ 06h 640x200 BW (CGA) 07h monochrome (MDA) ≥extended video modes (EGA/MCGA/VGA or other) ≥ 08h lores,16 color 09h med res,16 color ≥ 0Ah hires,4 color 0Bh n/a ≥ 0Ch med res,16 color 0Dh hires,16 color ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 0Eh hires,4 color 0Fh hires,64 color ≥40:4A≥ word ≥ # of columns on screen, coded as hex number of columns ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ 20 col = 14h (video mode 8, low res 160x200 CGA graphics) ≥ 40 col = 28h ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 80 col = 46h ≥40:4C≥ word ≥ screen buffer length in bytes √ƒƒƒƒƒ≈ƒƒƒƒƒƒƒ¥(# of bytes used per screen page, varies with video mode) ≥40:4E≥ word ≥ current screen buffer starting offset (active page) ≥40:50≥8 words≥ cursor position pages 1-8 ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ the first byte of each word gives the column (0-19, 39, ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ or 79) The second byte gives the row (0-24) ≥40:60≥ byte ≥ end line for cursor (normally 1) ≥40:61≥ byte ≥ start line for cursor (normally 0) ≥40:62≥ byte ≥ current video page being displayed (0-7) ≥40:63≥ word ≥ base port address of 6845 CRT controller or equivalent √ƒƒƒƒƒ≈ƒƒƒƒƒƒƒ¥ for active display 3B4h=mono, 3D4h=color ≥40:65≥ byte ≥ current setting of the CRT mode register ≥40:66≥ byte ≥ current palette mask setting (CGA) ≥40:67≥5 bytes≥ temporary storage for SS:SP during shutdown (cassette ≥ ≥ ≥ interface) ≥40:67≥2 bytes≥ Phoenix BIOS, address offset of option ROM ≥40:6C≥ word ≥ timer counter low word ≥40:6E≥ word ≥ timer counter high word ≥40:69≥2 bytes≥ Phoenix BIOS, address segment of option ROM ≥40:69≥ byte ≥ HD_INSTALL (Columbia PCs) (not valid on most clones) ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ bit 0 0 8 inch external floppy drives ≥ 1 5-1/4 external floppy drives ≥ 1,2 highest drive address which int 13 will ≥ accept (since the floppy drives are ≥ assigned 0-3, subtract 3 to obtain the number ≥ of hard disks installed) ≥ 4,5 # of hard disks connected to expansion ≥ controller ≥ 6,7 # of hard disks on motherboard controller ≥ (if bit 6 or 7 = 1, no A: floppy is present ≥ and the maximum number of floppies from int ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 11h is 3) ≥40:6B≥ byte ≥ last interrupt that occurred (used during POST only) ≥40:6C≥2 bytes≥ least significant timer count (ints 08h, 1Ah) ≥40:6E≥2 bytes≥ most significant timer count (ints 08h, 1Ah) ≥40:70≥ byte ≥ 24 hour timer overflow 1 if timer went past midnight √ƒƒƒƒƒ≈ƒƒƒƒƒƒƒ¥ it is reset to 0 each time it is read by int 1Ah ≥40:71≥ byte ≥ control-break flag (bit 7 = 1 means break key hit) ≥40:72≥ word ≥ reset flag ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ PCjr keeps 1234h here for softboot when a cartridge is ≥ inserted ≥ bits 1234h = soft reset, memory check will be bypassed ≥ 4321h = preserve memory (PS/2, Phoenix BIOS) ≥ 5678h = system suspended (Convertible) ≥ 9ABCh = manufacturing test mode (Convertible) ≥ ABCDh = system POST loop mode (Convertible) ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 0064h = burn-in mode (Phoenix BIOS) ≥40:74≥ byte ≥ status of last hard disk operation ; PCjr special disk ≥ ≥ ≥ control (see Chapter 8 for codes) ≥40:75≥ byte ≥ # of hard disks attached (0-2) ; PCjr special disk ≥ ≥ ≥ ; control ≥40:76≥ byte ≥ HD control byte; temporary holding area for 6th ≥ ≥ ≥ parameter table entry ≥40:77≥ byte ≥ port offset to current hd adapter ; PCjr special disk ≥ ≥ ≥ ; control ≥40:78≥4 bytes≥ timeout value for LPT1, LPT2, LPT3, LPT4 ≥40:7C≥4 bytes≥ timeout value for COM1, COM2, COM3, COM4 (0-0FFh secs, ≥ ≥ ≥ default 1) ≥40:80≥ word ≥ pointer to start of circular keyboard buffer, ≥ ≥ ≥ default 03:1E ≥40:82≥ word ≥ pointer to end of circular keyboard buffer, ≥ ≥ ≥ default 03:3E ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ note: early Zenith Z183 BIOS set these pointers to ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ zero and ignored them. ≥40:84≥ .... ≥ Video Control Data Area 2, 0040:0084 through 0040:008A ≥40:84≥ byte ≥ rows on the screen minus 1 (EGA only) ≥40:84≥ byte ≥ PCjr interrupt flag; timer channel 0 (used by POST) ≥40:84≥ byte ≥ early AT&T 6300 PCs put 35h here for some reason, ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ messing up programs that check here for number of screen ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ rows. Later versions of the 6300 put the screen rows here ≥40:85≥ word ≥ bytes per character (EGA only) ≥40:85≥2 bytes≥ (PCjr only) typamatic character to repeat ≥40:86≥2 bytes≥ (PCjr only) typamatic initial delay ≥40:87≥ byte ≥ mode options (EGA only) ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ bit 0 0 cursor emulation in effect ≥ 1 no cursor emulation ≥ 1 0 EGA is connected to a color display ≥ 1 EGA is connected to monochrome TTL display ≥ 2 0 wait for vertical retrace (CGA active) ≥ 1 don't wait for vertical retrace ≥ (EGA or MDA active) ≥ 3 0 EGA is the active display, ≥ 1 "other" display is active. ≥ 4 reserved ≥ 5,6 EGA memory size ≥ 0,0 64k ≥ 0,1 128k ≥ 1,0 192k ≥ 1,1 256k ≥ 7 0 don't clear screen on mode changes ≥ 1 if the last "set mode" specified not to ≥ clear the video buffer ≥ mode combinations: ≥ bit3 bit1 Meaning ≥ 0 0 EGA is active display and is color ≥ 0 1 EGA is active display and is monochrome ≥ 1 0 EGA is not active, a mono card is active ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 1 1 EGA is not active, a CGA is active ≥40:87≥ byte ≥ (PCjr only) current Fn key code √ƒƒƒƒƒ≈ƒƒƒƒƒƒƒ¥ 80h bit indicates make/break key code? ≥40:88≥ byte ≥ feature bits and switches (EGA only) 0=on, 1=off ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ bit 0 switch 1 ≥ 1 switch 2 ≥ 2 switch 3 ≥ 3 switch 4 ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 4-7 feature bits ≥40:88≥ byte ≥ (PCjr only) special keyboard status byte ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ bit 7 function flag ≥ 6 Fn-B break ≥ 5 Fn pressed ≥ 4 Fn lock ≥ 3 typamatic (0=enable,1=disable) ≥ 2 typamatic speed (0=slow,1=fast) ≥ 1 extra delay bef.typamatic (0=enable) ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 0 write char, typamatic delay elapsed ≥40:89≥ byte ≥ (PCjr) current value of 6845 reg 2 (horiz. synch) used ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ by ctrl-alt-cursor screen positioning routine in ROM ≥ (VGA) ≥ bit 0 reserved ≥ 1 video summing enabled ≥ 2 0 for color monitor attached ≥ 1 for mono monitor ≥ 3 0 for default palette loading enabled ≥ 4 0 for 8x8 text font ≥ 1 for 8x16 text font ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 5-7 reserved ≥40:8A≥ byte ≥ (PCjr) CRT/CPU Page Register Image, default 3Fh ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ (VGA) Display Combination Code Index. This is the value ≥ set/returned by function 1Ah of the Video BIOS. This ≥ byte contains an index into the ROM BIOS Display ≥ Combination Code table, which is a list of byte pairs ≥ that specify valid combinations of one or two video ≥ subsystems. Video subsystems are designated by the ≥ following values: ≥ 00h no display ≥ 01h MDA with monochrome display ≥ 02h CGA with color display ≥ 03h reserved ≥ 04h EGA with color display ≥ 05h EGA with monochrome display ≥ 06h Professional Graphics Adapter ≥ 07h VGA with analog monochrome display ≥ 08h VGA with analog color display ≥ 09h reserved ≥ 0Ah MCGA with digital color display ≥ 0Bh MCGA with analog monochrome display ≥ 0Ch MCGA with analog color display ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 0FFh unrecognized video subsystem ≥40:8B≥ byte ≥ last diskette data rate selected ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ bit 7,6 starting data transfer rate to use ≥ 0,0 500 kb/sec ≥ 0,1 300 kb/sec ≥ 1,0 250 kb/sec ≥ 1,1 reserved ≥ 5,4 last step rate selected ≥ 3 ending data transfer rate to use ≥ 2 reserved ≥ 1 reserved ≥ 0 1 combination floppy/fixed disk controller ≥ detected ≥ 0 XT floppy only controller (for 360kb drive) ≥ detected ≥ Data Transfer Rates ≥ Kbits/sec Media Drive Sectors/Track ≥ 250 360k 360k 9 ≥ 300 360k 1.2M 9 ≥ 500 1.2M 1.2M 15 ≥ 250 720k 720k 9 ≥ 250 720k 1.4M 9 ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 500 1.4M 1.4M 18 ≥40:8C≥ byte ≥ hard disk status returned by controller ≥40:8D≥ byte ≥ hard disk error returned by controller ≥40:8E≥ byte ≥ hard disk interrupt (bit 7 = working interrupt) ≥40:8F≥ byte ≥ combo_card - status of drives 0 and 1 (Tandy) ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ bit 7 reserved ≥ 6 drive type determined for drive 1 ≥ 5 drive multiple data rate capability for drive 1 ≥ 0 no multiple data rate ≥ 1 multiple data rate ≥ 4 1 then drive 1 has 80 tracks ≥ 0 then drive 1 has 40 tracks ≥ 3 reserved ≥ 2 drive type determined for drive 0 ≥ 1 drive multiple data rate capability for drive 0 ≥ 0 no multiple data rate ≥ 1 multiple data rate ≥ 0 1 the drive 0 has 80 tracks ≥ 0 the drive 0 has 40 tracks ≥ ≥ combo_card - status of drives 0 and 1 (Phoenix) ≥ bit 7 reserved ≥ 6 drive type determined for drive 1 ≥ 5 drive multiple data rate capability for drive 1 ≥ 0 no multiple data rate ≥ 1 multiple data rate ≥ 4 1 drive 1 supports change line ≥ 0 drive 1 does not support change line ≥ 3 reserved ≥ 2 drive type determined for drive 0 ≥ 1 drive multiple data rate capability for drive 0 ≥ 0 no multiple data rate ≥ 1 multiple data rate ≥ 0 1 drive 0 supports change line ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 0 drive 0 does not support change line ≥40:90≥2 bytes≥ media state drive 0, 1, 2, 3 ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ floppy_media_state ≥ bit 7,6 Data transfer rate ≥ 00 - 500 K/sec ≥ 01 - 300 K/sec ≥ 10 - 250 K/sec ≥ 11 - reserved ≥ 5 double stepping required ≥ 4 media/drive determined ≥ 3 reserved ≥ 2-0 present state ≥ 000 trying 360k in 360k drive (undetermined) ≥ 001 trying 360k in 1.2M drive (undetermined) ≥ 010 trying 1.2M in 1.2M drive (undetermined) ≥ 011 known 360k in 360k (determined) ≥ 100 known 360k in 1.2M (determined) ≥ 101 known 1.2M in 1.2M (determined) ≥ 110 reserved, not used ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 111 known 3.5" drive (determined) ≥40:92≥2 bytes≥ Diskette media work area. Each entry is first diskette ≥ ≥ ≥ media work area value tried. One byte per drive. Drive ≥ ≥ ≥ 0 at 92h, drive 1 at 93h. ≥40:94≥ byte ≥ current track number for drive 0 ≥40:95≥ byte ≥ current track number for drive 1 ≥40:96≥ byte ≥ keyboard flag byte 3 (see int 9h) ≥ ≥ ≥ bits 7 read ID in progress 3 right alt down ≥ ≥ ≥ 6 last code was first ID 2 left alt down ≥ ≥ ≥ 5 forced NumLock 1 last code was E0h ≥ ≥ ≥ 4 101/102 kbd used 0 last code was E1h ≥40:97≥ byte ≥ keyboard flag byte 2 (see int 9h) ≥ ≥ ≥ bits 7 keyboard error 3 reserved ≥ ≥ ≥ 6 LED update in progress 2 capslock LED status ≥ ≥ ≥ 5 kbd sent RESEND 1 numlock LED status ≥ ≥ ≥ 4 kbd sent ACK 0 scrollock LED status ≥40:98≥ word ≥ offset of user wait flag (int 08h, 15h, 1Ah) ≥40:9A≥ word ≥ segment of user wait flag (int 08h, 15h, 1Ah) ≥40:9C≥ word ≥ user wait timeout value in microseconds (low word) ≥40:9E≥ word ≥ user wait timeout value in microseconds (high word) ≥40:A0≥ byte ≥ real time clock wait function in use ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ bits 7 wait time elapsed and posted flag ≥ 6-1 reserved ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 0 int 15h, function 86h (WAIT) has occurred ≥40:A1≥ byte ≥ LAN A DMA channel flags ≥40:A2≥2 bytes≥ status LAN A 0,1 ≥40:A4≥ dword ≥ saved hard disk interrupt vector ≥40:A8≥ dword ≥ SAVE_PTR: EGA pointer to table of 7 parameters in ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ segment:offset format. Format of table: ≥ D_1 dword pointer to 1,472 byte table of 64 video parameters ≥ D_2 dword reserved ≥ D_3 dword reserved ≥ D_4 dword reserved ≥ D_5 dword reserved for future use ≥ D_6 dword reserved for future use ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ D_7 dword reserved for future use ≥40:B0≥2 words≥ international support (Tandy 1000 TX) ≥40:B4≥ byte ≥ keyboard NMI control flags (Convertible) ≥40:B4≥ byte ≥ monochrome monitor hookup detect (Tandy 1000 TX) ≥ ≥ ≥ 00h not present 0FFh present ≥40:B5≥ dword ≥ keyboard break pending flags (Convertible) ≥40:B5≥ byte ≥ extended equipment detect (5 bits) (Tandy 1000 TX) ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ bit 0 = 0 drive A is 5¨ ≥ 1 drive A is 3´ ≥ 1 = 0 drive B is 5¨ ≥ 1 drive B is 3´ ≥ 2 = 0 Tandy 1000 keyboard layout ≥ 1 IBM keyboard layout ≥ 3 = 0 CPU slow mode ≥ 1 CPU fast mode ≥ 4 = 0 internal color video support enabled ≥ 1 internal color video support disabled, ≥ external video enabled (chg from mb'd ≥ to expansion card) ≥ 5 = 0 no external monochrome video installed ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 1 external monochrome video installed ≥40:B6≥ byte ≥ extended equipment detect (1 bit) (Tandy 1000 TX) ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ bit 0 = 0 drive C is 5¨ ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 1 drive C is 3´ ≥40:B9≥ byte ≥ port 60 single byte queue (Convertible) ≥40:BA≥ byte ≥ scan code of last key (Convertible) ≥40:BB≥ byte ≥ pointer to NMI buffer head (Convertible) ≥40:BC≥ byte ≥ pointer to NMI buffer tail (Convertible) ≥40:BD≥16bytes≥ NMI scan code buffer (Convertible) ≥40:CE≥ word ≥ day counter (Convertible and after) ≥ to ≥ -04:CF≥ end of BIOS Data Area √ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ ≥ ** End of BIOS Data Area ** ≥ ** Beginning of "Extra Data Area" ** √ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ ≥40:D0≥-40:EF ≥ reserved by IBM ≥40:F0≥16bytes≥ Inter-Application Communications Area (for use by ≥40:FF≥ ≥ apps to transfer data or parameters to each other) ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ 1) Used by Turbo Power's FMARK (mark memory for TSRs). ≥ 2) Used by Norton Utilities' TimeMark to store the time. ≥ 3) Used by BRIEF editor. ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 4) TopView saves this area during task switches 5) Some 1992/1993 Phoenix BIOS used in Gateway 2000 486 DX/2 motherboards are buggy and corrupt this area. ≥50:00≥ byte ≥ DOS print screen status flag ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ 00h not active or successful completion ≥ 01h print screen in progress ⁄ƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¥ 0FFh error during print screen operation ≥50:01≥ ≥ Used by BASIC ≥50:02-03 ≥ PCjr POST and diagnostics work area ≥50:04≥ byte ≥ Single drive mode status byte - not used by AT&T DOS 2.11! ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ 00 logical drive A was last active ≥ 01 logical drive B was last active ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ 0FFh don't know (some DOS versions) ≥50:05-0E ≥ PCjr POST and diagnostics work area ≥50:0F≥ ≥ BASIC: SHELL flag (set to 02h if there is a current SHELL) ≥50:10≥ word ≥ BASIC: segment address storage (set with DEF SEG) ≥50:12≥4 bytes≥ BASIC: int 1Ch clock int vector segment:offset storage ≥50:16≥4 bytes≥ BASIC: int 23h ctrl-break int segment:offset storage ≥50:1A≥4 bytes≥ BASIC: int 24h disk error int vector segment:offset ≥50:1B-1F ≥ Used by BASIC for dynamic storage ≥50:20-21 ≥ Used by DOS for dynamic storage ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ According to the IBM TopView programmer's reference, ≥ 50:10 through 50:21 are used by BASIC, BASICA, and ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ programs compiled by the IBM BASIC Compiler. ≥50:22-2C ≥ Used by DOS for diskette parameter table. See int 1Eh ¿ƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¥ listing for values. In DOS 1.0 this is located in the ≥ ROM BIOS, but in DOS 1.1 and later it is a part of DOS ≥ located at 05:22. The first byte (out of eleven) of ≥ the Disk Parameter Table contains the hexadecimal value ≥ CF in DOS 1.0 and DF in DOS 1.1 and later. ≥ DOS 1.0 24ms ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ DOS 1.1 26ms ≥50:30-33 ≥ Used by MODE command ≥50:81≥ ≥ number of floppies installed in the system? ≥50:82≥ ≥ first hard disk drive? ≥50:83≥ ≥ last hard disk drive? ≥50:34-FF ≥ Unknown - Reserved for DOS ≥70:00 ≥ PC-MOS/386 loads into the lowest available memory, ≥ ≥ starting from this point. √ƒƒƒƒƒƒƒƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ ≥ ** End of "Extra Data Area" ** ≥ ** Beginning of "Extended Data Area" ** (Phoenix specs) ≥ ("EDA" is segment address of top of memory) √ƒƒƒƒƒƒ¬ƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ ≥EDA:00≥ byte ≥ Size of EDA in Kb (usually 1) ≥EDA:22≥ word ≥ pointing device driver FAR call offset ≥EDA:24≥ word ≥ pointing device driver FAR call segment ≥EDA:26≥ byte ≥ pointing device flag (first byte) ≥ ≥ ≥ bits 7 = 1 command in progress ≥ ≥ ≥ 6 = 1 resend ≥ ≥ ≥ 5 = 1 acknowlege ≥ ≥ ≥ 4 = 1 error ≥ ≥ ≥ 3 = 0 reserved ≥ ≥ ≥ 2-0 index count ≥EDA:27≥ byte ≥ pointing device flag (second byte) ≥ ≥ ≥ bits 7 device driver FAR call flag ≥ ≥ ≥ 6-3 = 0 reserved ≥ ≥ ≥ 2-0 package size ≥EDA:28≥ byte ≥ \ ≥ to ≥ ≥ pointing device data ≥EDA:2E≥ byte ≥ / ≥EDA:30≥ ≥ \ ≥ to ≥ ≥ reserved ≥EDA:38≥ ≥ / ≥EDA:39≥ word ≥ initial count for fail-safe timer ¿ƒƒƒƒƒƒ¡ƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ Absolute Addresses ............................................. 2**6 0008:0047 IO.SYS or IBMBIO.COM IRET instruction. This is the dummy routine that interrupts 01h, 03h, and 0Fh are initialized to during POST. C000:001E EGA BIOS signature (the letters IBM) F000:FA6E table of characters 00h-7Fh used by int 10h video BIOS The first 128 characters are stored here and each occupies 8 bytes. The high bit ones are somewhere on the video adapter card. F000:FFFE PC model identification. Note: some early IBM XTs return the PC ID code. Clones can return anything. To identify the submodel you need to do an int 15h, AH=0C0h (Return System Configuration Parameters). This call is not supported in early XT and AT BIOSes. FDFF:000E check this word value to identify GRiD machines: 00h GRiDCase (Old [first release] GRiDCase) 03h Tempest (Tempest GRiDCase) 04h GRiDCase Plus 14h GRiDLite 0Ch GRiDCase Plus Minus 34h GRiD 1520 (GRiD AT clone) 74h GRiD 1530 (GRiD-386) FE05B POST entry point (IBM standard addr.) FE2C3 NMI handler entry point (IBM standard addr.) FE3FE int 13h hard disk services entry point (IBM standard addr.) FE401 hard disk parameter table (IBM standard addr.) FE729 baud rate generator table (IBM standard addr.) FE739 int 14h async services entry point (IBM standard addr.) FE82E int 16h keyboard services entry point (IBM standard addr.) FE987 int 09h keyboard services entry point (IBM standard addr.) FEC59 int 13h diskette services entry point (IBM standard addr.) FEF57 int 0Eh diskette hardware ISR entry point (IBM standard addr.) FEFC7 diskette controller parameter table (IBM standard addr.) FEFD2 int 17h printer services entry point (IBM standard addr.) FF045 int 10h video services 0-Fh entry point (IBM standard addr.) FF065 int 10h video services entry point (IBM standard addr.) FF0A4 int 1Dh MDA/CGA video parameter table (IBM standard addr.) FF841 int 12h memory size service entry point (IBM standard addr.) FF84D int 11h equipment list service entry point(IBM standard addr.) FF859 int 15h System Services entry point (IBM standard addr.) FFA6E CGA font table (IBM standard addr.) FFE6E int 1Ah clock services entry point (IBM standard addr.) FFEA5 int 08h system timer ISR entry point (IBM standard addr.) FFEF3 initial int vector offsets loaded by POST (IBM standard addr.) FFF53 IRET opcode for dummy interrupt handler (IBM standard addr.) FFF54 int 05h print screen service entry point (IBM standard addr.) FFFF0 80x86 power-up entry point (part of the CPU) FFFFE system ID byte: (IBM standard addr.) ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥ ROM BIOS ⁄ model byte ≥ ≥ copyright ≥ ⁄ submodel byte machine ≥ ≥ date ≥ ≥ ⁄ revision ≥ √ƒƒƒƒƒƒƒƒƒƒ≈ƒƒƒƒ≈ƒƒƒƒ≈ƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ ≥ 00 ≥ 00 ≥ 00 ≥ AT&T 6300, Olivetti PC ≥ ≥ ≥ 2D ≥ -- ≥ -- ≥ Compaq PC (4.77mHz original) ≥ ≥ ≥ 30 ≥ -- ≥ -- ≥ Sperry PC (built by Mitsubishi) ≥ ≥ ≥ 86 ≥ -- ≥ -- ≥ HP-110 portable PC ≥ ≥ ≥ 9A ≥ -- ≥ -- ≥ Compaq Plus (XT compatible) ≥ ≥ 03/30/87 ≥ F8 ≥ 00 ≥ 00 ≥ PS/2 Model 80 8580-041 (16mhz) (-071?) ≥ ≥ 08/28/87 ≥ F8 ≥ ?? ≥ ?? ≥ PS/2 Model 80-071 16mHz 8580 ≥ ≥ 10/07/87 ≥ F8 ≥ 01 ≥ 00 ≥ PS/2 Model 80 8580-111/311 (20mhz) ≥ ≥ 09/17/87 ≥ F8 ≥ 01 ≥ 01 ≥ PS/2 Model 80-111 20mHz 8580 ≥ ≥ 11/21/89 ≥ ≥ ≥ ≥ PS/2 Model 80-Axx ≥ ≥ 04/11/88 ≥ F8 ≥ 04 ≥ 02 ≥ PS/2 Model 70-121 8570-121, 8570-E61 ≥ ≥ 04/11/88 ≥ F8 ≥ 09 ≥ 02 ≥ PS/2 Model 70 desktop ≥ ≥ 01/18/89 ≥ F8 ≥ 0B ≥ 00 ≥ PS/2 Model 70 Portable ≥ ≥ 01/18/89 ≥ ≥ ≥ ≥ PS/2 Model 73 ≥ ≥ 01/29/88 ≥ ≥ ≥ ≥ PS/2 Model 70 ≥ ≥ 03/17/89 ≥ ≥ ≥ ≥ PS/2 Model 70-061 ≥ ≥ 03/17/89 ≥ ≥ ≥ ≥ PS/2 Model 70-121 ≥ ≥ 02/20/89 ≥ ≥ ≥ ≥ PS/2 Model 70-A21 ≥ ≥ 02/20/89 ≥ ≥ ≥ ≥ PS/2 Model 70-A61 ≥ ≥ 10/02/89 ≥ ≥ ≥ ≥ PS/2 Model 70-B21 ≥ ≥ 12/01/89 ≥ ≥ ≥ ≥ PS/2 Model 70-A61 --> B61 ≥ ≥ 09/09/88 ≥ F8 ≥ 0B ≥ 01 ≥ PS/2 8573-??? ≥ ≥ ? ≥ F8 ≥ 0C ≥ 00 ≥ PS/2 8555-031/061 ≥ ≥ 02/20/89 ≥ F8 ≥ 0D ≥ ? ≥ PS/2 Model 70-A21 ≥ ≥ 06/22/88 ≥ F8 ≥ 0D ≥ 00 ≥ PS/2 Model 70 8570-A21 ≥ ≥ 09/13/85 ≥ F9 ≥ 00 ≥ 00 ≥ PC Convertible laptop ≥ ≥ 09/02/86 ≥ FA ≥ 00 ≥ 00 ≥ PS/2 Model 30 8530-021 ≥ ≥ 12/12/86 ≥ FA ≥ 00 ≥ 00 ≥ PS/2 Model 30 8530-021 ≥ ≥ 02/05/87 ≥ ≥ ≥ ≥ PS/2 Model 30 8530-021 ≥ ≥ 08/25/88 ≥ ≥ ≥ ≥ PS/2 Model 30 8530-E21 ≥ ≥ 05/16/88 ≥ ≥ ≥ ≥ PS/2 Model 30 8530-E21 ≥ ≥ 06/28/89 ≥ ≥ ≥ ≥ PS/2 Model 30 8530-Exx ≥ ≥ 06/26/87 ≥ FA ≥ 01 ≥ 00 ≥ PS/2 Model 25 8525 ≥ ≥ 01/10/86 ≥ FB ≥ 00 ≥ 00 ≥ XT-2 (early) ≥ ≥ 01/10/86 ≥ FB ≥ 00 ≥ 01 ≥ XT Model 089 (101-key keyboard ≥ ≥ 05/09/86 ≥ FB ≥ 01 ≥ 02 ≥ XT-2 (revised) (640k m'bd, 101 key k'bd ≥ ≥ 01/10/84 ≥ FC ≥ -- ≥ -- ≥ AT Model 099 (original 6mHz) ≥ ≥ 06/10/85 ≥ FC ≥ 00 ≥ 01 ≥ AT Model 5170-239 6mHz (6.6 max governor) ≥ ≥ 11/15/85 ≥ FC ≥ 01 ≥ 00 ≥ AT Model 5170-339 8mHz (8.6 max governor) ≥ ≥ ≥ FC ≥ 01 ≥ 00 ≥ Compaq 386/16 ≥ ≥ ≥ FC ≥ 01 ≥ 03 ≥ some Phoenix 386 BIOS ≥ ≥ ≥ FC ≥ 01 ≥ 81 ≥ some Phoenix 386 BIOS ≥ ≥ 04/21/86 ≥ FC ≥ 02 ≥ 00 ≥ XT/286 ≥ ≥ 02/13/87 ≥ FC ≥ 04 ≥ 00 ≥ PS/2 Model 50 8550-021 ≥ ≥ 12/22/86 ≥ FC ≥ 05 ≥ 00 ≥ PS/2 Model 60 8560 ≥ ≥ 02/13/87 ≥ FC ≥ 05 ≥ 00 ≥ PS/2 Model 60 8560 ≥ ≥ ≥ FC ≥ 00 ≥ ≥ 7531/2 Industrial AT ≥ ≥ ≥ FC ≥ 06 ≥ ≥ 7552 "Gearbox" ≥ ≥ 04/18/88 ≥ FC ≥ 04 ≥ 03 ≥ PS/2 50Z 8550-031/061 ≥ ≥ 01/24/90 ≥ FC ≥ 01 ≥ 00 ≥ Compaq Deskpro 80386/25e ≥ ≥ 10/02/89 ≥ FC ≥ 02 ≥ 00 ≥ Compaq Deskpro 386s, 386SX, 16mHz ≥ ≥ 08/25/88 ≥ FC ≥ 09 ≥ 00 ≥ 8530-Exx (286) ≥ ≥ 06/01/83 ≥ FD ≥ -- ≥ -- ≥ PCjr ≥ ≥ 11/08/82 ≥ FE ≥ -- ≥ -- ≥ XT, Portable PC, XT/370, 3270PC ≥ ≥ 04/24/81 ≥ FF ≥ -- ≥ -- ≥ PC-0 (original)(16k motherboard) ≥ ≥ 10/19/81 ≥ FF ≥ -- ≥ -- ≥ PC-1 (64k motherboard) ≥ ≥ 08/16/82 ≥ FF ≥ -- ≥ -- ≥ PC, XT, XT/370 (256k motherboard) ≥ ≥ 10/27/82 ≥ FF ≥ -- ≥ -- ≥ PC with HD/EGA BIOS upgrade chipset ≥ ≥ 02/08/90 ≥ ≥ ≥ ≥ PS/2 Model 65 ≥ ≥ 11/02/88 ≥ ≥ ≥ ≥ PS/2 Model 55SX ≥ ≥ 02/07/89 ≥ ≥ ≥ ≥ PS/2 Model 73-031 ≥ ¿ƒƒƒƒƒƒƒƒƒƒ¡ƒƒƒƒ¡ƒƒƒƒ¡ƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ The IBM PC System Interrupts (Overview) ........................ 2**7 The interrupt table is stored in the very lowest location in memory, starting at 0000:0000h. The locations are offset from segment 0, i.e. location 0000h has the address for int 0, etc. The table is 1024 bytes in length and contains 256 four byte vectors from 00h to 0FFh. Each address' location in memory can be found by multiplying the interrupt number by 4. For example, int 7 could be found by (7x4=28) or 1Bh (0000:001Bh). These interrupt vectors normally point to ROM tables or are taken over by DOS when an application is run. Some applications revector these interrupts to their own code to change the way the system responds to the user. DOS provides int 21h function 25h to change interrupts from a high level; altering the interrupt vector table directly is not recommended, nor would it really get you anywhere. Quick Chart of Interrupts 00h-0FFh ............................. 2**8 ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥ Interrupt Address ≥ ≥ √ƒƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¬ƒƒƒƒƒŸ Function ≥ ≥ Number≥ (Hex) ≥ Type ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 0 ≥ 00-03 ≥ CPU ≥ Divide by Zero ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 1 ≥ 04-07 ≥ CPU ≥ Single Step ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 2 ≥ 08-0B ≥ CPU ≥ Nonmaskable ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 3 ≥ 0C-0F ≥ CPU ≥ Breakpoint ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 4 ≥ 10-13 ≥ CPU ≥ Overflow ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 5 ≥ 14-17 ≥ BIOS≥ Print Screen ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 6 ≥ 18-1B ≥ hdw ≥ Reserved ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 7 ≥ 1C-1F ≥ hdw ≥ Reserved ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 8 ≥ 20-23 ≥ hdw ≥ Time of Day ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 9 ≥ 24-27 ≥ hdw ≥ Keyboard ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ A ≥ 28-2B ≥ hdw ≥ Reserved ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ B ≥ 2C-2F ≥ hdw ≥ Communications (8259) ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ C ≥ 30-33 ≥ hdw ≥ Communications ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ D ≥ 34-37 ≥ hdw ≥ Disk ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ E ≥ 38-3B ≥ hdw ≥ Diskette ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ F ≥ 3C-3F ≥ hdw ≥ Printer ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 10 ≥ 40-43 ≥ BIOS≥ Video ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 11 ≥ 44-47 ≥ BIOS≥ Equipment Check ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 12 ≥ 48-4B ≥ BIOS≥ Memory ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 13 ≥ 4C-4F ≥ BIOS≥ Diskette/Disk ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 14 ≥ 50-53 ≥ BIOS≥ Serial Communications ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 15 ≥ 54-57 ≥ BIOS≥ Cassette, System Services ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 16 ≥ 58-5B ≥ BIOS≥ Keyboard ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 17 ≥ 5C-5F ≥ BIOS≥ Parallel Printer ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 18 ≥ 60-63 ≥ BIOS≥ ROM BASIC Loader ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 19 ≥ 64-67 ≥ BIOS≥ Bootstrap Loader ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 1A ≥ 68-6B ≥ BIOS≥ Time of Day ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 1B ≥ 6C-6F ≥ BIOS≥ Keyboard Break ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 1C ≥ 70-73 ≥ BIOS≥ Timer Tick ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 1D ≥ 74-77 ≥ BIOS≥ Video Initialization ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 1E ≥ 78-7B ≥ BIOS≥ Diskette Parameters ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 1F ≥ 7C-7F ≥ BIOS≥ Video Graphics Characters, second set ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 20 ≥ 80-83 ≥ DOS ≥ General Program Termination ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 21 ≥ 84-87 ≥ DOS ≥ DOS Services Function Request ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 22 ≥ 88-8B ≥ DOS ≥ Called Program Termination Address ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 23 ≥ 8C-8F ≥ DOS ≥ Control Break Termination Address ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 24 ≥ 90-93 ≥ DOS ≥ Critical Error Handler ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 25 ≥ 94-97 ≥ DOS ≥ Absolute Disk Read ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 26 ≥ 98-9B ≥ DOS ≥ Absolute Disk Write ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 27 ≥ 9C-9F ≥ DOS ≥ Terminate and Stay Resident ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 28-3F ≥ A0-FF ≥ DOS ≥ Reserved for DOS ≥ ¿ƒƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¡ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ *29h Fast Screen Write ≥ ≥ *2Ah Microsoft Networks - Session Layer ≥ ≥ Interrupt ≥ ≥ 2Fh Multiplex Interrupt ≥ ≥ *30h Far jump instruction for CP/M-style ≥ ≥ calls ≥ ≥ 33h Used by Microsoft Mouse Driver ≥ ⁄ƒƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¬ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 40-43 ≥100-115≥ BIOS≥ Reserved for BIOS ≥ ¿ƒƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¡ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 40h Hard Disk BIOS ≥ ≥ 41h Hard Disk Parameters (except PC1) ≥ ≥ 42h Pointer to screen BIOS entry (EGA, VGA,≥ ≥ PS/2) ≥ ≥ 43h Pointer to EGA initialization parameter ≥ ≥ table ≥ ⁄ƒƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¬ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 44 ≥116-119≥ BIOS≥ First 128 Graphics Characters ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 45-47 ≥120-131≥ BIOS≥ Reserved for BIOS ≥ ¿ƒƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¡ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 45h Reserved by IBM (not initialized) ≥ ≥ 46h Pointer to hard disk 2 params (AT, PS/2)≥ ≥ 47h Reserved by IBM (not initialized) ≥ ⁄ƒƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¬ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 48 ≥132-135≥ BIOS≥ PCjr Cordless Keyboard Translation ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 49 ≥136-139≥ BIOS≥ PCjr Non-Keyboard Scancode Translation Table ≥ ¿ƒƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¡ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 4Ah Real-Time Clock Alarm (Convertible, ≥ ≥ PS/2) ≥ ⁄ƒƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¬ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 50-5F ≥140-17F≥ BIOS≥ Reserved for BIOS ≥ ¿ƒƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¡ƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 5Ah Cluster Adapter BIOS entry address ≥ ≥ *5Bh IBM (cluster adapter?) ≥ ≥ 5Ch NETBIOS interface entry port ≥ ⁄ƒƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¬ƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 60-67 ≥180-19F≥ User Program Interrupts (availible for general use) ≥ ¿ƒƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¡ƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 60h 10-Net Network ≥ ≥ 67h Used by LIM & AQA EMS, EEMS ≥ ⁄ƒƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¬ƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 68-7F ≥1A0-1FF≥ Reserved by IBM ≥ ¿ƒƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¡ƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 6Ch System Resume Vector (Convertible) ≥ ≥ 6Fh some Novell and 10-Net API functions ≥ ≥ 70h IRQ 8, Real Time Clock Interrupt (AT, ≥ ≥ PS/2) ≥ ≥ 71h IRQ 9, LAN Adapter 1 ≥ ≥ 72h IRQ 10 (AT, XT/286, PS/2) Reserved ≥ ≥ 73h IRQ 11 (AT, XT/286, PS/2) Reserved ≥ ≥ 74h IRQ 12 Mouse Interrupt (PS/2) ≥ ≥ 75h IRQ 13, Coprocessor Error ≥ ≥ 76h IRQ 14, Hard Disk Controller (AT, PS/2) ≥ ≥ 77h IRQ 15 (AT, XT/286, PS/2) Reserved ≥ ≥ 7Ch IBM REXX88PC command language ≥ ⁄ƒƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒ¬ƒƒƒƒƒ¡ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 80-85 ≥200-217≥ ROM BASIC ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ 86-F0 ≥218-3C3≥ Used by BASIC Interpreter When BASIC is running ≥ √ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒ≈ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ F1-FF ≥3C4-3FF≥ Reserved by IBM ≥ ¿ƒƒƒƒƒƒƒ¡ƒƒƒƒƒƒƒ¡ƒƒƒƒƒƒ¬ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ¥ ≥ *0F8h Set Shell Interrupt (OEM) ≥ ≥ *0F9h OEM SHELL service codes ≥ ¿ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ IRQ Usage Chart ................................................ 2**9 The 8259-1 Programmable Interrupt Controller (PIC) has eight interrupt request (IRQ) levels. Lower numbered IRQs have higher priority. On AT and PS/2 machines, a second 8259 chip is cascaded off the IRQ2 channel. Channels marked with an asterisk (*) are normally available. (IRQ0) 55ms timer "tick" issued 18.2 times per second. (IRQ1) keyboard *(IRQ2) for ATs, IRQ2 is used to support the second interrupt controller. In this case, int 71h (IRQ 9) is used to replace IRQ 2. Hardware calls to int 71h are redirected to this interrupt to maintain compatibility. IRQ 8 Real Time Clock Interrupt (AT, PS/2) * IRQ 9 LAN Adapter 1 * IRQ 10 (AT, XT/286, PS/2) Reserved * IRQ 11 (AT, XT/286, PS/2) Reserved * IRQ 12 used by EISA machines, also PS/2 Mouse Interrupt IRQ 13 Coprocessor Error IRQ 14 Hard Disk Controller (AT, PS/2) * IRQ 15 (AT, XT/286, PS/2) Reserved *(IRQ3) Serial Port 2 (COM2) *(IRQ4) Serial Port 1 (COM1) or internal modem in PCjr or Convertible *(IRQ5) XT hard disk, free on standard AT (IRQ6) floppy controller (IRQ7) LPT1, LPT2 Two cards generally cannot share the same IRQ without conflict on ISA bus machines. EISA and PS/2 machines can share IRQs, but require specially designed cards to do so. The IBM-PC System Interrupts (in detail) ....................... 2**10 ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥Interrupt 00h Divide by Zero ≥ ¿ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ (0:0000h) (processor error). Automatically called at end of DIV or IDIV operation that results in error. Normally set by DOS to display an error message and abort the program. note 1) On an 8086/8088, the return address points to the following instruction. 2) On an 80286/80386, the return address points to the divide instruction. 3) Trapped by PC-MOS/386 to provide a default handler for divide overflow conditions. If the application does not have its own handler, MOS will terminate the program with an appropriate message. ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥Interrupt 01h Single Step ≥ ¿ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ (0:0004h) Taken after every instruction when CPU Trap Flag indicates single-step mode (bit 8 of FLAGS is 1). This is what makes the "T" command of DEBUG work for single stepping. Is not generated after MOV to segment register or POP of segment register. (unless you have a very early 8088 with the microcode bug). ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥Interrupt 02h Non-Maskable Interrupt (NMI) ≥ ¿ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ (0:0008h) Vector not disabled via CLI. Generated by NMI signal in hardware. This function is called in the event of a memory parity error or may occur in the event of other hardware problems or failures depending on the specific manufacturer's hardware. Displays the appropriate error message and halts the processor. Some AT chip sets apparently use int 02h to signal I/O errors as well as parity errors. This signal has various uses: POST parity error: all except PCjr & Convertible 80x87 coprocessor interrupt: all except PCjr & Convertible Keyboard interrupt: PCjr, Convertible I/O channel check: Convertible, PS/2 50+ Disk controller power-on request: Convertible System suspend: Convertible Realtime clock: Convertible System watchdog timer: PS/2 50+ Timeout interrupt: PS/2 50+ DMA timer time-out interrupt: PS/2 50+ Infrared keyboard link: PCjr ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥Interrupt 03h Breakpoint ≥ ¿ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ (0:000Ch) Taken when CPU executes the 1-byte int 3 (0CCh). Similar to (internal) the 8080's RST instruction. Generally used to set breakpoints for DEBUG. note 1) Also used by Turbo Pascal versions 1,2,3 when {$U+} specified. 2) Int 3s are sometimes inserted by the Microsoft Linker in response to an unresolved symbol. ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥Interrupt 04h Divide overflow ≥ ¿ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ (0:0010h) Generated by INTO instruction if OF flag is set. If the (internal) flag is not set, INTO is effectively a NOP. Used to trap any arithmetic errors when program is ready to handle them rather than immediately when they occur. ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥Interrupt 05h Print Screen ≥ ¿ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ (0:0014h) Service dumps the screen to the printer. Invoked by int 9 for shifted key 55 (PrtSc). Automatically called by the keyboard scan when PrtSc key is pressed. Normally executes a routine to print the screen, but may call any routine that can safely be executed from inside the keyboard handler. Status and result bytes are at address 0050:0000. (internal) BOUND Check Failed (80286+) Generated by BOUND instruction when the value to be tested is less than the indicated lower bound or greater than the indicated upper bound. entry AH 05h return absolute address 50:0 00h print screen has not been called, or upon return from a call there were no errors 01h print screen is already in progress 0FFh error encountered during printing note 1) Uses BIOS services to read the screen. 2) Output is directed to LPT1. 3) Revectored into GRAPHICS.COM if GRAPHICS.COM is loaded. 4) On the Tandy 1000TX this interrupt can be enabled or disabled across the expansion slots via a DIP switch. 5) With early versions of DOS 5.0, at PrtScr of a graphics display gets garbage when GRAPHICS.COM is loaded. This was fixed in one of the first updates. ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥Interrupt 06h Reserved by IBM ≥ ¿ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ (0:0018h) On the Tandy 1000TX this interrupt can be enabled or disabled across the expansion slots via a DIP switch. PC-MOS/386 in 386 mode uses this interrupt to signal memory allocation errors. The CS:IP of the offending instruction is placed on the stack. (internal) Undefined Opcode (80286+) ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥Interrupt 07h Reserved by IBM ≥ ¿ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ (0:00C0h) On the Tandy 1000TX this interrupt can be enabled or disabled across the expansion slots via a DIP switch. (internal) No Math Unit Available (80286+) note The 80286 and later can be programmed to generate an int 7 whenever an ESC instruction is encountered. This could be used to emulate an 80x87 series coprocessor in software and be transparent to the application software. It could also be used to make a non-Intel floating point processor emulate an 80x87. ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥Interrupt 08h Timer ≥ ¿ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ (0:0020h) 55ms timer "tick" issued 18.2 times per second. (IRQ0) 8259-1 Interrupt Controller Updates the system time at [0040:006C] (low word) and [0040:006E] (high word) and issues an int 1Ch (timer). (Int 1Ch points to an IRET instruction unless changed by a resident program). The timer interrupt is given the highest maskable interrupt priority upon power up. (internal) Double Fault (80286+ protected mode) Called when multiple exceptions occur on one instruction, or an exception occurs in an exception handler. If an exception occurs in the double fault handler, the CPU goes into SHUTDOWN mode (which circuitry in the PC/AT converts to a reset). entry AH 08h return absolute addresses: 40:6C number of interrupts since power on (4 bytes) 40:70 number of days since power on (1 byte) 40:67 day counter on all products after AT 40:40 motor control count - gets decremented and shuts off diskette motor if zero note 1) IBM PC LAN 1.2 and PC/MOS-386 require this count be 18.2Hz and will report errors if the timer rate is reprogrammed. 2) Some "turbo" XT clones were shipped with slower-than-18.2Hz timers so they would appear faster to benchmark software. Caveat emptor. 3) Trapped by PC-MOS/386 to ensure task switching is performed. This interrupt should never be disabled when running PC-MOS. 4) Trapped by Quarterdeck's DESQview. ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥Interrupt 09h Keyboard ≥ ¿ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ (0:0024h) Taken whenever a key is pressed or released. This is (IRQ1) normally a scan code, but may also be an ACK or NAK of a command on AT-type keyboards. The hardware provides the key pressed in a non-ASCII scan code format read at I/O port 60h. The servicer acknowledges receipt of the key by toggling bit 7 of port 61h. (Port 61h should be read first, then bit 7 ORed on, output to port 61h, then ANDed off, and resent to port 61h). The read key is decoded to yield an ASCII character, special function key (such as F1) or a control function like Left Shift Key. The converted ASCII character is placed into the next available position in the circular keyboard queue. It is put in the position indicated by queue tail when it will not cause the loss of earlier entered data. The queue head points to the oldest key pressed in the buffer which has not been removed from the queue (the normal process uses int 16h to remove keys from the queue and return the key value to the int 16h caller). The 16 word queue holds up to 16 keys. If the queue head equals the queue tail, the queue is empty. Valid keys in the queue comprise the upper byte scan code and the lower byte ASCII character. If the key pressed has no ASCII equivalent (i.e F1 to F12), the lower byte is zero. Toggle and shift keys are not placed in the buffer, but appear in the two status bytes at absolute addresses 0040:0017 and 0040:0018. Special key combinations will cause other events to occur: a) Ctrl-Alt-Del - Reboot computer b) Print screen - Call int 05h to print the current screen c) Ctrl-Break - Call int 1Bh control-break key processor (DOS) (internal) Math Unit Protection Fault (80286+ protected mode) entry AH 09h return at absolute memory addresses: 40:17 bit 0 right shift key depressed 1 left shift key depressed 2 control key depressed 3 alt key depressed 4 ScrollLock state has been toggled 5 NumLock state has been toggled 6 CapsLock state has been toggled 7 insert state is active 40:18 bit 0 left control key depressed 1 left alt key depressed 2 SysReq key depressed 3 Pause key has been toggled 4 ScrollLock key is depressed 5 NumLock key is depressed 6 CapsLock key is depressed 7 Insert key is depressed 40:96 bit 0 last code was the E1h hidden code 1 last code was the E0h hidden code 2 right control key down 3 right alt key down 4 101 key Enhanced keyboard installed 5 force NumLock if rd ID & kbx 6 last character was first ID character 7 doing a read ID (must be bit 0) 40:97 bit 0 ScrollLock indicator 1 NumLock indicator 2 CapsLock indicator 3 circus system indicator 4 ACK received 5 resend received flag 6 mode indicator update 7 keyboard transmit error flag 40:1E keyboard buffer (20h bytes) 40:1C buffer tail pointer 40:72 1234h if ctrl-alt-del pressed on keyboard AL scan code note 1) Int 05h invoked if PrtSc key pressed. 2) Int 1Bh invoked if Ctrl-Break key sequence pressed. 3) Int 15h, AH=85h invoked on AT and after if SysReq key is pressed. 4) Int 15h, AH=4Fh invoked on machines after AT. 5) Int 16h, BIOS keyboard functions, uses this interrupt. 6) PC-MOS/386 will issue this interrupt for keystrokes ocurring on remote serial terminals to simulate local access. ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥Interrupt 0Ah EGA Vertical Retrace ≥ ¿ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ (0:0028h) used by EGA vertical retrace (IRQ2) 8259-1 Interrupt Controller note 1) The TOPS and PCnet adapters use this IRQ line by default. 2) On systems equipped with 2 interrupt controller chips (8259), IRQ 2 is used to support the second interrupt controller. In this case, int 71h (IRQ 9) is used to replace IRQ 2. Hardware calls to int 71h are redirected to this interrupt to maintain compatibility. 3) IRQ 2 is used for vertical retrace signal on PS/2s with VGA on the motherboard. Most aftermarket VGA boards to not use this interrupt. 4) Some early Samsung machines routed IRQ2 to the onboard system clock and did not continue IRQ2 to the I/O bus. 5) The Roland LAPC-1 board uses IRQ2. 6) Elographics touchscreens use optionally use IRQ2. (internal) Invalid Task State Segment (80286+ protected mode) ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥Interrupt 0Bh Communications Controller (serial port) hdw. entry ≥ ¿ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ (0:002Ch) Serial Port 2 (COM2) 8259-1 (IRQ3) note 1) IRQ 3 may be used by SDLC (synchronous data-link control) or bisynchronous communications cards instead of a serial port. 2) The TOPS and PCnet adapters use this interrupt request line as an alternate. 3) On PS/2s, COM2 through COM8 share this IRQ. 4) For most serial boards, COM4 shares this IRQ. 5) On the Commodore Amiga 2000 with the PC Bridge Board, this interrupt is used for communication between the Amiga system board and the Bridge Board. This was probably the lowest IRQ level they felt safe using, but limits the A2000's use of network cards, etc. 6) This interrupt is used by part of the stack-switching code added to DOS 3.2 for use with Local Area Network adapters. 7) The PS/2 puts COM3 through COM8 at port addresses above 3FFh (not properly decoded by older PCs) and has all of them sharing IRQ3. 8) Toshiba 1600 laptop normally connects IRQ3 only to internal modem slot. You must run FORCE3.COM from Toshiba to enable IRQ3 for the expansion slot. 9) The BIOS Data Area was not set up to point to COM2 on POST in some early IBM PS/2 Model 50Z machines. 10) Marstek 105 scanner - optional IRQ. 11) Elographics touchscreens use optionally use IRQ 3. 12) Default for Stargate Plus 8 multiport serial board. 13) Tecmar/Wangtek PC-36 tape controller board - default IRQ. 14) Older versions of Microsoft BASICA pretty well booger the IRQ and port addresses for the serial ports when they exit. (internal) Not Present (80286+ protected mode) Generated when loading a segment register if the segment descriptor indicates that the segment is not currently in memory. May be used to implement virtual memory. ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥Interrupt 0Ch COM1 Serial Port ≥ ¿ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ (0:0030h) Serial Port 1 (COM1) or internal modem in PCjr or Convertible (IRQ4) 8259-1 note 1) IRQ 4 may be used by SDLC (synchronous data-link control) or bisynchronous communications cards instead of a serial port. 2) On some PCs, this interrupt is shared by COM3. 3) Some Tandy computers use IRQ4 instead of IRQ5 for the hard disk interrupt. 4) Best performance of mice sometimes happens when they are configured for IRQ4 instead of IRQ3, since some mouse drivers may lock system interrupts for long periods. 5) Elographics touchscreens use optionally use IRQ 4. 6) Older versions of Microsoft BASICA pretty well booger the IRQ and port addresses for the serial ports when they exit. (internal) Stack Fault (80286+ protected mode) Generated on stack overflow/underflow. Note that the 80286 will shut down in real mode if SP=1 before a push. ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥Interrupt 0Dh Hard Disk ≥ ¿ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ (0:0034h) Miscellaneous uses (IRQ5) 8259-1 note 1) Various Tandy 1000 models may use this line for the 60Hhz RAM refresh or as "optional bus interrupt." 2) Used by hard disk on IBM XT and most compatibles. 3) LPT2 on AT, XT/286, and PS/2 4) Dummy CRT vertical retrace on PCjr 5) Marstek 105 scanner - default IRQ. 6) Elographics touchscreens use IRQ 5 (2,3,4 & 7 also selectable) (internal) General Protection Violation (80286+) Called in real mode when an instruction attempts to access a word operand located at offset 0FFFFh or a PUSH MEM or POP MEM instruction contains an invalid bit code in the second byte, or when an instruction exceeds the maximum length allowed (10 bytes for 80286, 15 bytes for 80386) ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥Interrupt 0Eh Diskette Interrupt ≥ ¿ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ (0:0038h) Generated by floppy controller on completion of an operation (IRQ6) (sets bit 8 of 40:3E) note Tecmar PC-36 tape controllers use this setting by default, as they are not intended to be used when floppies are to be accessed. (internal) Page Fault (80386+ native mode) ⁄ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒø ≥Interrupt 0Fh Reserved by IBM ≥ ¿ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒŸ (0:003Ch) IRQ7 used by 8259 PPI interrupt (LPT1, LPT2) (IRQ7) note 1) Generated by the LPT1 printer adapter when printer becomes ready. Many printer adapters do not reliably generate this interrupt. 2) This interrupt is normally avoided. If a bad interrupt occurs, it will vector to this spot (when caused by a misprogrammed 8259 PIC) 3) According to the Creative Labs Sound Blaster board docs, some Tandy 1000 models use this interrupt internally. 4) Elographics touchscreens use optionally use IRQ 7.