Updated PC programming documentation
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Jeff Parsons
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pubs/pc/programming/Programming_Technical_Reference/chap2.txt
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CHAPTER 2
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Programming Technical Reference - IBM
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Copyright 1988, Dave Williams
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CPU Port Assignments, System Memory Map, BIOS Data Area, Interrupts 00h to 09h
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SYSTEM MEMORY MAP - OVERALL
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The IBM PC handles its address space in 64k segments, divided into 16k
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fractions and then further as nescessary.
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start start end
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addr. addr. addr. usage
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(dec) (hex)
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00000 **** 640k *************** system data, drivers....
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0000:0000 hardware interrupt vectors
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0000:0040 BIOS interrupt vectors
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0k start of RAM | 0000:0080 DOS interrupt vector table
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16k 00000-03FFF | 0000:0300 Stack area during POST and bootstrap routine
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32k 04000-07FFF | 0000:0400 BIOS Data Area
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48k 08000-0BFFF | 0000:04F0 Intra-Application Communications Area
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64k 10000-13FFF | 0000:0500 DOS reserved communication area
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80k 14000-17FFF | xxxx:0000 IO.SYS - DOS interface to ROM I/O routines
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96k 18000-1BFFF | xxxx:0000 MSDOS.SYS - DOS interrupt handlers, service
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112k 1C000-1FFFF | routines (int 21 functions)
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128k 20000-23FFF | xxxx:xxxx DOS buffers, control areas, and installed
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144k 24000-27FFF | device drivers.
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160k 28000-2BFFF | xxxx:0000 resident portion of COMMAND.COM, interrupt
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176k 2C000-2FFFF | handlers for int 22h, 23h,24h, and code to
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| reload the transient portion
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192k 30000-33FFF | xxxx:0000 master environment block, default 64 bytes
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208k 34000-37FFF | xxxx:0000 environment for next program
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224k 38000-3BFFF | xxxx:0000 external commands or utilities (COM or EXE
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240k 3C000-3FFFF | files)
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256k 40000-43FFF | ----:---- application programs
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272k 44000-47FFF | xxxx:0000 user stack for COM files (256 bytes)
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288k 48000-4BFFF | xxxx:0000 transient portion of COMMAND.COM
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304k 4C000-4FFFF |
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320k 50000-53FFF |
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336k 54000-57FFF |
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352k 58000-5BFFF |
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368k 5C000-5FFFF |
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384k 60000-63FFF |
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400k 64000-67FFF |
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416k 68000-6BFFF |
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432k 6C000-6FFFF |
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448k 70000-73FFF |
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464k 74000-77FFF |
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480k 78000-7BFFF |
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496k 7C000-7FFFF |
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512k 80000-83FFF |
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528k 84000-87FFF |
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544k 88000-8BFFF | original IBM PC-1 BIOS limited memory to 544k
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560k 8C000-8FFFF |
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576k 90000-93FFF |
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592k 94000-97FFF |
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609k 98000-9BFFF |
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624k 9C000-9FFFF | to 640k (top of RAM address space)
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A0000 ***** 64k *************** EGA address
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640k A0000-A95B0 MCGA 320x200 256 color video buffer
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AF8C0 MCGA 640x480 2 color video buffer
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-A3FFF
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656k A4000-A7FFF
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672k A8000-ABFFF
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688k AC000-AFFFF
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B0000 ***** 64k *************** mono and CGA address
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704k B0000-B3FFF mono uses only 4k | The PCjr and early Tandy 1000
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720k B4000-B7FFF | BIOSs revector direct writes to
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736k B8000-BBFFF CGA uses entire 16k | the B8 area to the Video Gate
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756k BC000-BFFFF | Array and reserved system RAM
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C0000 ***** 64k *************** expansion ROM
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768k C0000-C3FFF 16k EGA BIOS C000:001E EGA BIOS signature (the letters IBM)
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784k C4000-C5FFF
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C6000-C63FF 256 bytes Professional Graphics Display communication area
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C6400-C7FFF
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800k C8000-CBFFF 16k hard disk controller BIOS, drive 0 default
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816k CC000-CDFFF 8k IBM PC Network NETBIOS
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CE000-CFFFF
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D0000 ***** 64k *************** expansion ROM | PCjr first ROM cartridge
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832k D0000-D7FFF 32k IBM Cluster Adapter | address area.
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DA000 voice communications |
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848k D4000-D7FFF | Common expanded memory board
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864k D8000-DBFFF | paging area.
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880k DC000-DFFFF |
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E0000 ***** 64k *************** expansion ROM | PCjr second ROM
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896k E0000-E3FFF | cartridge address
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912k E4000-E7FFF | area
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928k E8000-EBFFF |
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944k EC000-EFFFF |
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F0000 ***** 64k *************** system | PCjr optional ROM
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960k F0000-F3FFF reserved by IBM | cartridge address
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976k F4000- | area (cartridge
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F6000 ROM BASIC Begins | BASIC)
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992k F8000-FB000 |
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1008k FC000-FFFFF ROM BASIC and original |
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BIOS (Compatibility BIOS |
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in PS/2) |
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1024k FFFFF end of memory (1024k) for 8088 machines
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F000:FFF5 BIOS release date
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F000:FFFE PC model identification
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384k 100000-15FFFF 80286/AT extended memory area, 1Mb motherboard
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15Mb 100000-FFFFFF 80286/AT extended memory address space
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15Mb 160000-FDFFFF Micro Channel RAM expansion (15Mb extended memory)
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128k FE0000-FFFFFF system board ROM (PS/2 Advanced BIOS)
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PC Port Assignment, Intel 8088, 80C88, 8086, 80286, 80386 CPUs
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hex addr. Function
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0000-000F 8237 DMA controller
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0010-001F 8237 DMA controller (AT, PS/2)
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0020-0027 8259A interrupt controller
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0020-003F 8259A interrupt controller (AT)
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0040-005F 8253-5 programmable timers
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(note: 0041 was memory refresh in PCs. Not used in PS/2)
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0060-0067 8255 peripheral interface
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0060-006F 8042 keyboard controller (AT)
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0200-020F game-control adapter
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0210-0217 expansion box (PC, XT)
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0278-027F LPT3
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02F8-02FF COM2
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0300-031F prototype card
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0320-032F hard disk controller
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0378-037F LPT2
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03BC-03BF LPT1
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03D0-03DF CGA, MCGA, VGA adapter control
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03F0-03F7 floppy disk controller
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03F8-03FF COM1
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note: These are functions common across the IBM range. The PCjr, PC
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Convertible and PS/2 (both buses) have enhancements. In some cases, the
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AT and PS/2 series ignore, duplicate, or reassign ports arbitrarily. If
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your code incorporates specific port addresses for video or system board
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control it would be wise to have your application determine the machine
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type and video adapter and address the ports as required.
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Reserved Memory Locations in the IBM PC
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addr. size description
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000h-3FFh DOS interrupt vector table
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30:00h- used as a stack area during POST and bootstrap routines. This
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3F:FFh stack area may be revectored by an application program.
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The BIOS Data Area addr. from 400h to 4FFh
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40:00 word COM1 port address | These addresses are zeroed out in the
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40:02 word COM2 port address | OS/2 DOS Compatibility Box if any of
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40:04 word COM3 port address | the OS/2 COM??.SYS drivers are loaded.
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40:06 word COM4 port address |
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40:08 word LPT1 port address
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40:0A word LPT2 port address
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40:0C word LPT3 port address
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40:0E word LPT4 port address (not valid in PS/2 machines)
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40:0E word PS/2 pointer to 1k extended BIOS Data Area at top of RAM
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40:10 word equipment flag (see int 11h)
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bits:
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0 1 if floppy drive present (see bits 6&7) 0 if not
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1 1 if 80x87 installed (not valid in PCjr)
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2,3 system board RAM (not used on AT or PS/2)
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00 16k
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01 32k
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10 48k
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11 64k
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4,5 initial video mode
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00 no video adapter
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01 40 column color (PCjr)
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10 80 column color
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11 MDA
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6,7 number of diskette drives
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00 1 drive
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01 2 drives
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10 3 drives
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11 4 drives
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8 0 DMA present
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1 DMA not present (PCjr)
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9,A,B number of RS232 serial ports
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C game adapter (joystick)
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0 no game adapter
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1 if game adapter
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D serial printer (PCjr only)
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0 no printer
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1 serial printer present
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E,F number of parallel printers installed
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note 1) The IBM PC and AT store the settings of the system board
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switches or CMOS RAM setup information (as obtained by the BIOS
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in the Power-On Self Test (POST)) at addresses 40:10h and
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40:13h. 00000001b indicates "on", 00000000b is "off".
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2) CMOS RAM map, PC/AT:
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offset contents
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00h Seconds
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01h Second Alarm
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02h Minutes
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03h Minute Alarm
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04h Hours
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05h Hour Alarm
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06h Day of the Week
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07h Day of the Month
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08h Month
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09h Year
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0Ah Status Register A
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0Bh Status Register B
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0Ch Status Register C
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0Dh Status Register D
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0Eh Diagnostic Status Byte
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0Fh Shutdown Status Byte
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10h Disk Drive Type for Drives A: and B:
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The drive-type bytes use bits 0:3 for the first
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drive and 4:7 for the other
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Disk drive types:
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00h no drive present
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01h double sided 360k
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02h high capacity (1.2 meg)
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03h-0Fh reserved
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11h (AT):Reserved (PS/2):drive type for hard disk C:
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12h (PS/2):drive type for hard disk D:
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(AT, XT/286):hard disk type for drives C: and D:
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Format of drive-type entry for AT, XT/286:
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0 number of cyls in drive (0-1023 allowed)
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2 number of heads per drive (0-15 allowed)
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3 starting reduced write compensation (not
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used on AT)
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5 starting cylinder for write compensation
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7 max. ECC data burst length, XT only
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8 control byte
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Bit
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7 disable disk-access retries
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6 disable ECC retries
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5-4 reserved, set to zero
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3 more than 8 heads
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2-0 drive option on XT (not used by AT)
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9 timeout value for XT (not used by AT)
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12 landing zone cylinder number
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14 number of sectors per track (default 17,
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0-17 allowed)
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13h Reserved
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14h Equipment Byte (corresponds to sw. 1 on PC and XT)
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15h-16h Base Memory Size (low,high)
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17h-18h Expansion Memory Size (low,high)
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19h-20h Reserved
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(PS/2) POS information Model 50 (60 and 80 use a 2k
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CMOS RAM that is not accessible through software)
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21h-2Dh Reserved (not checksumed)
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2Eh-2Fh Checksum of Bytes 10 Through 20 (low,high)
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30h-31h Exp. Memory Size as Det. by POST (low,high)
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32h Date Century Byte
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33h Information Flags (set during power-on)
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34h-3Fh Reserved
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3) The alarm function is used to drive the BIOS wait function (int
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15h function 90h).
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4) To access the configuration RAM write the byte address (00-3Fh)
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you need to access to I/O port 70h, then access the data via I/O
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port 71h.
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5) CMOS RAM chip is a Motorola 146818
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6) The equipment byte is used to determine the configuration for the
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power-on diagnostics.
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7) Bytes 00-0Dh are defined by the chip for timing functions, bytes
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0Eh-3Fh are defined by IBM.
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40:12 byte number of errors detected by infrared keyboard link (PCjr only)
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40:13 word availible memory size in Kbytes (less display RAM in PCjr)
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this is the value returned by int 12h
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40:17 byte keyboard flag byte 0 (see int 9h)
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bit 7 insert mode on 3 alt pressed
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6 capslock on 2 ctrl pressed
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5 numlock on 1 left shift pressed
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4 scrollock on 0 right shift pressed
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40:18 byte keyboard flag byte 1 (see int 9h)
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bit 7 insert pressed 3 ctrl-numlock (pause) toggled
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6 capslock pressed 2 PCjr keyboard click active
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5 numlock pressed 1 PCjr ctrl-alt-capslock held
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4 scrollock pressed 0
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40:19 byte storage for alternate keypad entry (not normally used)
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40:1A word pointer to keyboard buffer head character
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40:1C word pointer to keyboard buffer tail character
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40:1E 32bytes 16 2-byte entries for keyboard circular buffer, read by int 16h
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40:3E byte drive seek status - if bit=0, next seek will recalibrate by
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repositioning to Track 0.
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bit 3 drive D bit 2 drive C
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1 drive B 0 drive A
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40:3F byte diskette motor status
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bit 7 1, write in progress 3 1, D: motor on (floppy 3)
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6 2 1, C: motor on (floppy 2)
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5 1 1, B: motor on
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4 0 1, A: motor on
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40:40 byte motor off counter
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starts at 37 and is decremented 1 by each system clock tick.
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motor is shut off when count = 0.
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40:41 byte status of last diskette operation where:
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bit 7 timeout failure bit 3 DMA overrun
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6 seek failure 2 sector not found
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5 controller failure 1 address not found
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4 CRC failure 0 bad command
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40:42 7 bytes NEC status
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40:49 byte current CRT mode (hex value)
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00h 40x25 BW (CGA) 01h 40x25 color (CGA)
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02h 80x25 BW (CGA) 03h 80x25 color (CGA)
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04h 320x200 color (CGA) 05h 320x200 BW (CGA)
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06h 640x200 BW (CGA) 07h monochrome (MDA)
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extended video modes (EGA/MCGA/VGA or other)
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08h lores,16 color 09h med res,16 color
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0Ah hires,4 color 0Bh n/a
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0Ch med res,16 color 0Dh hires,16 color
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0Eh hires,4 color 0Fh hires,64 color
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40:4A word number of columns on screen, coded as hex number of columns
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20 col = 14h (video mode 8, low resolution 160x200 CGA graphics)
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40 col = 28h
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80 col = 46h
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40:4C word screen buffer length in bytes
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(number of bytes used per screen page, varies with video mode)
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40:4E word current screen buffer starting offset (active page)
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40:50 8 words cursor position pages 1-8
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the first byte of each word gives the column (0-19, 39, or 79)
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the second byte gives the row (0-24)
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40:60 byte end line for cursor (normally 1)
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40:61 byte start line for cursor (normally 0)
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40:62 byte current video page being displayed (0-7)
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40:63 word base port address of 6845 CRT controller or equivalent
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for active display 3B4h=mono, 3D4h=color
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40:65 byte current setting of the CRT mode register
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40:66 byte current palette mask setting (CGA)
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40:67 5 bytes temporary storage for SS:SP during shutdown (cassette interface)
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40:6C word timer counter low word
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40:6E word timer counter high word
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40:69 byte HD_INSTALL (Columbia PCs) (not valid on most clone computers)
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bit 0 = 0 8 inch external floppy drives
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1 5-1/4 external floppy drives
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1,2 = highest drive address which int 13 will accept
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(since the floppy drives are assigned 0-3, subtract
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3 to obtain the number of hard disks installed)
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4,5 = # of hard disks connected to expansion controller
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6,7 = # of hard disks on motherboard controller
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(if bit 6 or 7 = 1, no A: floppy is present and
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the maximum number of floppies from int 11 is 3)
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40:70 byte 24 hour timer overflow 1 if timer went past midnight
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it is reset to 0 each time it is read by int 1Ah
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40:71 byte BIOS break flag (bit 7 = 1 means break key hit)
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40:72 word reset flag (1234 = soft reset, memory check will be bypassed)
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PCjr keeps 1234h here for softboot when a cartridge is installed
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40:74 byte status of last hard disk operation; PCjr special diskette control
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40:75 byte # of hard disks attached (0-2) ; PCjr special diskette control
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40:76 byte hd control byte; temporary holding area for 6th param table entry
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40:77 byte port offset to current hd adapter ; PCjr special diskette control
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40:78 4 bytes timeout value for LPT1,LPT2,LPT3,LPT4
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40:7C 4 bytes timeout value for COM1,COM2,COM3,COM4 (0-FFh seconds, default 1)
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40:80 word pointer to start of circular keyboard buffer, default 03:1E
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40:82 word pointer to end of circular keyboard buffer, default 03:3E
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40:84 byte rows on the screen (EGA only)
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40:84 byte PCjr interrupt flag; timer channel 0 (used by POST)
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40:85 word bytes per character (EGA only)
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40:85 2 bytes (PCjr only) typamatic char to repeat
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40:86 2 bytes (PCjr only) typamatic initial delay
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40:87 byte mode options (EGA only)
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Bit 1 0 = EGA is connected to a color display
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1 = EGA is monochrome.
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Bit 3 0 = EGA is the active display,
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1 = "other" display is active.
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Mode combinations:
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Bit3 Bit1 Meaning
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0 0 EGA is active display and is color
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0 1 EGA is active display and is monochrome
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1 0 EGA is not active, a mono card is active
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1 1 EGA is not active, a CGA is active
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40:87 byte (PCjr only) current Fn key code
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40:88 byte feature bit switches (EGA only) 0=on, 1=off
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bit 3 = switch 4
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bit 2 = switch 3
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bit 1 = switch 2
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bit 0 = switch 1
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40:88 byte (PCjr only) special keyboard status byte
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bit 7 function flag 3 typamatic (0=enable,1=disable)
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6 Fn-B break 2 typamatic speed (0=slow,1=fast)
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5 Fn pressed 1 extra delay bef.typamatic (0=enable)
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4 Fn lock 0 write char, typamatic delay elapsed
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40:89 byte PCjr, current value of 6845 reg 2 (horiz.synch) used by
|
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ctrl-alt-cursor screen positioning routine in ROM
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40:8A byte PCjrCRT/CPU Page Register Image, default 3Fh
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40:8B byte last diskette data rate selected
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40:8C byte hard disk status returned by controller
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40:8D byte hard disk error returned by controller
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40:8E byte hard disk interrupt (bit 7=working int)
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40:90 4 bytes media state drive 0, 1, 2, 3
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40:94 2 bytes track currently seeked to drive 0, 1
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40:96 byte keyboard flag byte 3 (see int 9h)
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40:97 byte keyboard flag byte 2 (see int 9h)
|
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40:98 dword pointer to users wait flag
|
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40:9C dword users timeout value in microseconds
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40:A0 byte real time clock wait function in use
|
||||
40:A1 byte LAN A DMA channel flags
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40:A2 2 bytes status LAN A 0,1
|
||||
40:A4 dword saved hard disk interrupt vector
|
||||
40:A8 dword EGA pointer to parameter table
|
||||
40:B4 byte keyboard NMI control flags (Convertible)
|
||||
40:B5 dword keyboard break pending flags (Convertible)
|
||||
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 -04:8F end of BIOS Data Area
|
||||
40:90-40:EF reserved by IBM
|
||||
04:F0 16 bytes Intra-Application Communications Area (for use by applications
|
||||
04:FF to transfer data or parameters to each other)
|
||||
|
||||
05:00 byte DOS print screen status flag
|
||||
00h not active or successful completion
|
||||
01h print screen in progress
|
||||
0FFh error during print screen operation
|
||||
05:01 Used by BASIC
|
||||
05:02-03 PCjr POST and diagnostics work area
|
||||
05:04 byte Single drive mode status byte
|
||||
00 logical drive A
|
||||
01 logical drive B
|
||||
05:05-0E PCjr POST and diagnostics work area
|
||||
05:0F BASIC: SHELL flag (set to 02h if there is a current SHELL)
|
||||
05:10 word BASIC: segment address storage (set with DEF SEG)
|
||||
05:12 4 bytes BASIC: int 1Ch clock interrupt vector segment:offset storage
|
||||
05:16 4 bytes BASIC: int 23h ctrl-break interrupt segment:offset storage
|
||||
05:1A 4 bytes BASIC: int 24h disk error interrupt vector segment:offset storage
|
||||
05:1B-1F Used by BASIC for dynamic storage
|
||||
05:20-21 Used by DOS for dynamic storage
|
||||
05:22-2C Used by DOS for diskette parameter table. See int 1Eh for values
|
||||
05:30-33 Used by MODE command
|
||||
05:34-FF Unknown - Reserved for DOS
|
||||
|
||||
|
||||
At Absolute Addresses:
|
||||
|
||||
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:FFF5 BIOS release date
|
||||
F000:FFFE PC model identification
|
||||
date model byte submodel byte revision
|
||||
04/24/81 FF = PC-0 (16k) -- --
|
||||
10/19/81 FF = PC-1 (64k) -- --
|
||||
08/16/82 FF = PC, XT, XT/370 -- --
|
||||
(256k motherboard)
|
||||
10/27/82 FF = PC, XT, XT/370 -- --
|
||||
(256k motherboard)
|
||||
11/08/82 FE = XT, Portable PC -- --
|
||||
XT/370, 3270PC
|
||||
01/10/86 FB = XT 00 01
|
||||
01/10/86 FB = XT-2 (early)
|
||||
05/09/86 FB = XT-2 (640k) 00 02
|
||||
06/01/83 FD = PCjr -- --
|
||||
01/10/84 FC = AT -- --
|
||||
06/10/85 FC = AT 00 01
|
||||
11/15/85 FC = AT 01 00
|
||||
04/21/86 FC = XT/286 02 00
|
||||
09/13/85 F9 = Convertible 00 00
|
||||
09/02/86 FA = PS/2 Model 30 00 00
|
||||
11/15/86 FC = AT, Enhanced 8mHz
|
||||
02/13/87 FC = PS/2 Model 50 04 00
|
||||
02/13/87 FC = PS/2 Model 60 05 00
|
||||
1987 F8 = PS/2 Model 80 00 00
|
||||
2D = Compaq PC (4.77) -- --
|
||||
9A = Compaq Plus (XT) -- --
|
||||
|
||||
00FC 7531/2 Industrial AT
|
||||
06FC 7552 Gearbox
|
||||
|
||||
|
||||
|
||||
|
||||
The IBM PC System Interrupts (Overview)
|
||||
|
||||
The interrupt table is stored in the very lowest location in memory, starting
|
||||
at 0000:0000h. The locations are offset from segment 0, ie location 0000h has
|
||||
the address for int 0, etc. Each address is four bytes long and its 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.
|
||||
|
||||
Interrupt Address Function
|
||||
Number (Hex)
|
||||
0 00-03 CPU Divide by Zero
|
||||
1 04-07 CPU Single Step
|
||||
2 08-0B CPU Nonmaskable
|
||||
3 0C-0F CPU Breakpoint
|
||||
4 10-13 CPU Overflow
|
||||
5 14-17 BIOS Print Screen
|
||||
6 18-1B hdw Reserved
|
||||
7 1C-1F hdw Reserved
|
||||
8 20-23 hdw Time of Day
|
||||
9 24-27 hdw Keyboard
|
||||
A 28-2B hdw Reserved
|
||||
B 2C-2F hdw Communications [8259]
|
||||
C 30-33 hdw Communications
|
||||
D 34-37 hdw Disk
|
||||
E 38-3B hdw Diskette
|
||||
F 3C-3F hdw Printer
|
||||
10 40-43 BIOS Video
|
||||
11 44-47 BIOS Equipment Check
|
||||
12 48-4B BIOS Memory
|
||||
13 4C-4F BIOS Diskette/Disk
|
||||
14 50-53 BIOS Serial Communications
|
||||
15 54-57 BIOS Cassette, System Services
|
||||
16 58-5B BIOS Keyboard
|
||||
17 5C-5F BIOS Parallel Printer
|
||||
18 60-63 BIOS Resident BASIC
|
||||
19 64-67 BIOS Bootstrap Loader
|
||||
1A 68-6B BIOS Time of Day
|
||||
1B 6C-6F BIOS Keyboard Break
|
||||
1C 70-73 BIOS Timer Tick
|
||||
1D 74-77 BIOS Video Initialization
|
||||
1E 78-7B BIOS Diskette Parameters
|
||||
1F 7C-7F BIOS Video Graphics Characters, second set
|
||||
20 80-83 DOS General Program Termination
|
||||
21 84-87 DOS DOS Services Function Request
|
||||
22 88-8B DOS Called Program Termination Address
|
||||
23 8C-8F DOS Control Break Termination Address
|
||||
24 90-93 DOS Critical Error Handler
|
||||
25 94-97 DOS Absolute Disk Read
|
||||
26 98-9B DOS Absolute Disk Write
|
||||
27 9C-9F DOS Terminate and Stay Resident
|
||||
28-3F A0-FF DOS Reserved for DOS
|
||||
40-43 100-115 BIOS Reserved for BIOS
|
||||
44 116-119 BIOS First 128 Graphics Characters
|
||||
45-47 120-131 BIOS Reserved for BIOS
|
||||
48 132-135 BIOS PCjr Cordless Keyboard Translation
|
||||
49 136-139 BIOS PCjr Non-Keyboard Scancode Translation Table
|
||||
50-5F 140-17F BIOS Reserved for BIOS
|
||||
60-67 180-19F Reserved for User Software Interrupts
|
||||
68-7F 1A0-1FF Reserved by IBM
|
||||
80-85 200-217 ROM BASIC
|
||||
86-F0 218-3C3 Used by BASIC Interpreter When BASIC is Running
|
||||
F1-FF 3C4-3FF Reserved by IBM
|
||||
|
||||
|
||||
For consistency in this volume, 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.
|
||||
|
||||
|
||||
The IBM-PC System Interrupts (in detail)
|
||||
|
||||
|
||||
Interrupt 00h Divide by Zero (processor error). Automatically called at end
|
||||
(0:0000h) of DIV or IDIV operation that results in error. Normally set by
|
||||
DOS to display an error message and abort the program.
|
||||
|
||||
|
||||
Interrupt 01h Single step - Taken after every instruction when CPU Trap Flag
|
||||
(0:0004h) 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).
|
||||
|
||||
|
||||
Interrupt 02h Non-maskable interrupt - Vector not disabled via CLI. Used by
|
||||
(0:0008h) parity check routine in POST, 8087 coprocessor, PCjr infrared
|
||||
keyboard link.
|
||||
|
||||
|
||||
Interrupt 03h Breakpoint - Taken when CPU executes the 1-byte int 3 (0CCh).
|
||||
(0:000Ch) Generated by opcode 0CCh. Similar to 8080's RST instruction.
|
||||
Generally used to set breakpoints for DEBUG.
|
||||
|
||||
|
||||
Interrupt 04h Divide overflow - Generated by INTO instruction if OF flag is
|
||||
(0:0010h) set. If 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.
|
||||
|
||||
|
||||
Interrupt 05h Print Screen - service dumps the screen to the printer. Invoked
|
||||
(0:0014h) by int 9 for shifted key 55 (PrtSc). Automatically called by
|
||||
keyboard scan when PrtSc key is pressed. Normally executes
|
||||
routine to print the screen, but may call any routine that can
|
||||
safely be executed from inside the keyboard scanner. Status and
|
||||
result byte are at address 0050:0000.
|
||||
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
|
||||
|
||||
|
||||
Interrupt 06h Reserved by IBM
|
||||
(0:0018h)
|
||||
|
||||
|
||||
Interrupt 07h Reserved by IBM
|
||||
(0:00C0h)
|
||||
|
||||
|
||||
Interrupt 08h Timer - 55ms timer "tick" taken 18.2 times per second. Updates
|
||||
(0:0020h) (IRQ0) BIOS clock and turns off diskette drive motors after 2
|
||||
seconds of inactivity.
|
||||
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 Int 1Ch invoked as a user interrupt.
|
||||
|
||||
|
||||
Interrupt 09h Keyboard - taken whenever a key is pressed or released.
|
||||
(0:0024h) (IRQ1) Stores characters/scan-codes in status at [0040:0017,18]
|
||||
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
|
||||
|
||||
|
||||
Interrupt 0Ah EGA Vertical Retrace
|
||||
(0:0028h) (IRQ2) used by EGA vertical retrace, hard disk
|
||||
|
||||
|
||||
Interrupt 0Bh Communications Controller (serial port) hdw. entry
|
||||
(0:002Ch) (IRQ3) Serial Port 2 (com2)
|
||||
note IRQ 3 may be used by SDLC (synchronous data-link control) or
|
||||
bisynchronous communications cards instead of a serial port.
|
||||
|
||||
|
||||
Interrupt 0Ch Communications Controller (serial port) hdw. entry
|
||||
(0:0030h) (IRQ4) Serial Port 1 (com1)
|
||||
note IRQ 4 may be used by SDLC (synchronous data-link control) or
|
||||
bisynchronous communications cards instead of a serial port.
|
||||
|
||||
|
||||
Interrupt 0Dh Alternate Printer, PC/AT 80287
|
||||
(0:0034h) (IRQ5) used by hard disk, 60 Hz RAM refresh, LPT2 on AT, XT/286,
|
||||
and PS/2, dummy CRT vertical retrace on PCjr
|
||||
|
||||
|
||||
Interrupt 0Eh Diskette - indicates that a seek is in progress
|
||||
(0:0038h) (IRQ6) (sets bit 8 of 40:3E)
|
||||
|
||||
|
||||
Interrupt 0Fh Reserved by IBM
|
||||
(0:003Ch) (IRQ7) IRQ7 used by PPI interrupt (LPT1, LPT2)
|
||||
|
||||
Loading…
Reference in a new issue