biosdataarea.txt

会变语言实现的一些程序

BDA - BIOS Data Area - PC Memory Map
   Address Size      Description
   00:00 256dwords Interrupt vector table
   30:00 256bytes   Stack area used during post and bootstrap
   40:00   word   COM1 port address
   40:02   word   COM2 port address
   40:04   word   COM3 port address
   40:06   word   COM4 port address
   40:08   word   LPT1 port address
   40:0A   word   LPT2 port address
   40:0C   word   LPT3 port address
   40:0E   word   LPT4 port address (except PS/2)
         Extended BIOS Data Area segment (PS/2, see EBDA)
   40:10  2 bytes   Equipment list flags (see INT 11)
      |7|6|5|4|3|2|1|0| 40:10 (value in INT 11 register AL)
       | | | | | | | `- IPL diskette installed
       | | | | | | `-- math coprocessor
       | | | | |-+--- old PC system board RAM < 256K
       | | | | | `-- pointing device installed (PS/2)
       | | | | `--- not used on PS/2
       | | `------ initial video mode
       `--------- # of diskette drives, less 1
      |7|6|5|4|3|2|1|0| 40:11  (value in INT 11 register AH)
       | | | | | | | `- 0 if DMA installed
       | | | | `------ number of serial ports
       | | | `------- game adapter
       | | `-------- not used, internal modem (PS/2)
       `----------- number of printer ports
   40:12   byte   PCjr: infrared keyboard link error count
   40:13   word   Memory size in Kbytes  (see INT 12)
   40:15   byte   Reserved
   40:16   byte   PS/2 BIOS control flags
   40:17   byte   Keyboard flag byte 0 (see KB FLAGS)
      |7|6|5|4|3|2|1|0| keyboard flag byte 0
       | | | | | | | `--- right shift key depressed
       | | | | | | `---- left shift key depressed
       | | | | | `----- CTRL key depressed
       | | | | `------ ALT key depressed
       | | | `------- scroll-lock is active
       | | `-------- num-lock is active
       | `--------- caps-lock is active
       `---------- insert is active
   40:18   byte   Keyboard flag byte 1 (see KB FLAGS)
      |7|6|5|4|3|2|1|0| keyboard flag byte
       | | | | | | | `--- left CTRL key depressed
       | | | | | | `---- left ALT key depressed
       | | | | | `----- system key depressed and held
       | | | | `------ suspend key has been toggled
       | | | `------- scroll lock key is depressed
       | | `-------- num-lock key is depressed
       | `--------- caps-lock key is depressed
       `---------- insert key is depressed
   40:19   byte   Storage for alternate keypad entry
   40:1A   word   Offset from 40:00 to keyboard buffer head
   40:1C   word   Offset from 40:00 to keyboard buffer tail
   40:1E  32bytes   Keyboard buffer (circular queue buffer)
   40:3E   byte   Drive recalibration status
      |7|6|5|4|3|2|1|0| drive recalibration status
       | | | | | | | `-- 1=recalibrate drive 0
       | | | | | | `--- 1=recalibrate drive 1
       | | | | | `---- 1=recalibrate drive 2
       | | | | `----- 1=recalibrate drive 3
       | `---------- unused
       `----------- 1=working interrupt flag
   40:3F   byte   Diskette motor status
      |7|6|5|4|3|2|1|0| diskette motor status
       | | | | | | | `-- 1=drive 0 motor on
       | | | | | | `--- 1=drive 1 motor on
       | | | | | `---- 1=drive 2 motor on
       | | | | `----- 1=drive 3 motor on
       | `---------- unused
       `----------- 1=write operation
   40:40   byte   Motor shutoff counter (decremented by INT 8)
   40:41   byte   Status of last diskette operation (see INT 13,1)
      |7|6|5|4|3|2|1|0| status of last diskette operation
       | | | | | | | `--- invalid diskette command
       | | | | | | `---- diskette address mark not found
       | | | | | `----- sector not found
       | | | | `------ diskette DMA error
       | | | `------- CRC check / data error
       | | `-------- diskette controller failure
       | `--------- seek to track failed
       `---------- diskette time-out
   40:42  7 bytes   NEC diskette controller status (see FDC)
   40:49   byte   Current video mode  (see VIDEO MODE)
   40:4A   word   Number of screen columns
   40:4C   word   Size of current video regen buffer in bytes
   40:4E   word   Offset of current video page in video regen buffer
   40:50  8 words   Cursor position of pages 1-8, high order byte=row
         low order byte=column; changing this data isn't
         reflected immediately on the display
   40:60   byte   Cursor ending (bottom) scan line (don't modify)
   40:61   byte   Cursor starting (top) scan line (don't modify)
   40:62   byte   Active display page number
   40:63   word   Base port address for active 6845 CRT controller
         3B4h = mono, 3D4h = color
   40:65   byte   6845 CRT mode control register value (port 3x8h)
         EGA/VGA values emulate those of the MDA/CGA
   40:66   byte   CGA current color palette mask setting (port 3d9h)
         EGA and VGA values emulate the CGA
   40:67   dword   CS:IP for 286 return from protected mode
      dword   Temp storage for SS:SP during shutdown
      dword   Day counter on all products after AT
      dword   PS/2 Pointer to reset code with memory preserved
      5 bytes   Cassette tape control (before AT)
   40:6C   dword   Daily timer counter, equal to zero at midnight;
         incremented by INT 8; read/set by INT 1A
   40:70   byte   Clock rollover flag, set when 40:6C exceeds 24hrs
   40:71   byte   BIOS break flag, bit 7 is set if Ctrl-Break was
         *ever* hit; set by INT 9
   40:72   word   Soft reset flag via Ctl-Alt-Del or JMP FFFF:0
         1234h  Bypass memory tests & CRT initialization
         4321h  Preserve memory
         5678h  System suspend
         9ABCh  Manufacturer test
         ABCDh  Convertible POST loop
         ????h  many other values are used during POST
   40:74   byte   Status of last hard disk operation (see INT 13,1)
   40:75   byte   Number of hard disks attached
   40:76   byte   XT fixed disk drive control byte
   40:77   byte   Port offset to current fixed disk adapter
   40:78  4 bytes   Time-Out value for LPT1,LPT2,LPT3(,LPT4 except PS/2)
   40:7C  4 bytes   Time-Out value for COM1,COM2,COM3,COM4
   40:80   word   Keyboard buffer start offset (seg=40h,BIOS 10-27-82)
   40:82   word   Keyboard buffer end offset (seg=40h,BIOS 10-27-82)
   40:84   byte   Rows on the screen (less 1, EGA+)
   40:85   word   Point height of character matrix (EGA+)
      byte   PCjr: character to be repeated if the typematic
         repeat key takes effect
   40:86   byte   PCjr: initial delay before repeat key action begins
   40:87   byte   PCjr: current Fn function key number
      byte   Video mode options (EGA+)
      |7|6|5|4|3|2|1|0| Video mode options (EGA+)
       | | | | | | | `-- 1=alphanumeric cursor emulation enabled
       | | | | | | `--- 1=video subsystem attached to monochrome
       | | | | | `---- reserved
       | | | | `----- 1=video subsystem is inactive
       | | | `------ reserved
       | `--------- video RAM  00-64K  10-192K  01-128K  11-256K
       `---------- video mode number passed to INT 10, function 0
   40:88   byte   PCjr: third keyboard status byte
         EGA feature bit switches, emulated on VGA
      |7|6|5|4|3|2|1|0| EGA feature bit switches (EGA+)
       | | | | | | | `-- EGA SW1 config (1=off)
       | | | | | | `--- EGA SW2 config (1=off)
       | | | | | `---- EGA SW3 config (1=off)
       | | | | `----- EGA SW4 config (1=off)
       | | | `------ Input FEAT0 (ISR0 bit 5) after output on FCR0
       | | `------- Input FEAT0 (ISR0 bit 6) after output on FCR0
       | `-------- Input FEAT1 (ISR0 bit 5) after output on FCR1
       `--------- Input FEAT1 (ISR0 bit 6) after output on FCR1
   40:89   byte   Video display data area (MCGA and VGA)
      |7|6|5|4|3|2|1|0| Video display data area (MCGA and VGA)
       | | | | | | | `-- 1=VGA is active
       | | | | | | `--- 1=gray scale is enabled
       | | | | | `---- 1=using monochrome monitor
       | | | | `----- 1=default palette loading is disabled
       | | | `------ see table below
       | | `------- reserved
       | `--------  1=display switching enabled
       `--------- alphanumeric scan lines (see table below)
         Bit7    Bit4   Scan Lines
      0   0   350 line mode
      0   1   400 line mode
      1   0   200 line mode
      1   1   reserved
   40:8A   byte   Display Combination Code (DCC) table index (EGA+)
   40:8B   byte   Last diskette data rate selected
      |7|6|5|4|3|2|1|0| last diskette data rate selected
       | | | | `--------- reserved
       | | `------------ last floppy drive step rate selected
       `-------------- last floppy data rate selected
      Data Rate          Step Rate
      00  500K bps      00  step rate time of 0C
      01  300K bps      01  step rate time of 0D
      10  250K bps      10  step rate time of 0A
      11  reserved      11  reserved
   40:8C   byte   Hard disk status returned by controller
   40:8D   byte   Hard disk error returned by controller
   40:8E   byte   Hard disk interrupt control flag(bit 7=working int)
   40:8F   byte   Combination hard/floppy disk card when bit 0 set
   40:90  4 bytes   Drive 0,1,2,3 media state
      |7|6|5|4|3|2|1|0| drive media state (4 copies)
       | | | | | `------- drive/media state (see below)
       | | | | `------- reserved
       | | | `------- 1=media/drive established
       | | `------- double stepping required
       `--------- data rate:   00=500K bps    01=300K bps
               10=250K bps    11=reserved
      Bits
      210  Drive Media State
      000  360Kb diskette/360Kb drive not established
      001  360Kb diskette/1.2Mb drive not established
      010  1.2Mb diskette/1.2Mb drive not established
      011  360Kb diskette/360Kb drive established
      100  360Kb diskette/1.2Mb drive established
      101  1.2Mb diskette/1.2Mb drive established
      110  Reserved
      111  None of the above
   40:94   byte   Track currently seeked to on drive 0
   40:95   byte   Track currently seeked to on drive 1
   40:96   byte   Keyboard mode/type
      |7|6|5|4|3|2|1|0| Keyboard mode/type
       | | | | | | | `--- last code was the E1 hidden code
       | | | | | | `---- last code was the E0 hidden code
       | | | | | `----- right CTRL key depressed
       | | | | `------ right ALT key depressed
       | | | `------- 101/102 enhanced keyboard installed
       | | `-------- force num-lock if Rd ID & KBX
       | `--------- last char was first ID char
       `---------- read ID in process
   40:97   byte   Keyboard LED flags
      |7|6|5|4|3|2|1|0| Keyboard LED flags
       | | | | | | | `--- scroll lock indicator
       | | | | | | `---- num-lock indicator
       | | | | | `----- caps-lock indicator
       | | | | `------ circus system indicator
       | | | `------- ACK received
       | | `-------- re-send received flag
       | `--------- mode indicator update
       `---------- keyboard transmit error flag
   40:98   dword   Pointer to user wait complete flag
   40:9C   dword   User wait Time-Out value in microseconds
   40:A0   byte   RTC wait function flag
      |7|6|5|4|3|2|1|0| INT 15,86 RTC wait function flag
       | | | | | | | `--- 1= wait pending
       | `-------------- not used
       `--------------- 1=INT 15,86 wait time elapsed
   40:A1   byte   LANA DMA channel flags
   40:A2  2 bytes   Status of LANA 0,1
   40:A4   dword   Saved hard disk interrupt vector
   40:A8   dword   BIOS Video Save/Override Pointer Table address
         (see VIDEO TABLES)
   40:AC  8 bytes   Reserved
   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   NMI buffer head pointer (convertible)
   40:BC   byte   NMI buffer tail pointer (convertible)
   40:BD  16bytes   NMI scan code buffer (convertible)
   40:CE   word   Day counter (convertible and after)
   40:F0  16bytes   Intra-Applications Communications Area (IBM Technical
         Reference incorrectly locates this at 50:F0-50:FF)
   Address Size      Description    (BIOS/DOS Data Area)
   50:00   byte   Print screen status byte
          00 = PrtSc not active,
          01 = PrtSc in progress
          FF = error
   50:01  3 bytes   Used by BASIC
   50:04   byte   DOS single diskette mode flag, 0=A:, 1=B:
   50:05  10bytes   POST work area
   50:0F   byte   BASIC shell flag; set to 2 if current shell
   50:10   word   BASICs default DS value (DEF SEG)
   50:12   dword   Pointer to BASIC INT 1C interrupt handler
   50:16   dword   Pointer to BASIC INT 23 interrupt handler
   50:1A   dword   Pointer to BASIC INT 24 disk error handler
   50:20   word   DOS dynamic storage
   50:22  14bytes   DOS diskette initialization table (INT 1E)
   50:30   4bytes   MODE command
   70:00      I/O drivers from IO.SYS/IBMBIO.COM

The following map varies in size and locus
   07C0:0      Boot code is loaded here at startup (31k mark)
   A000:0      EGA/VGA RAM for graphics display mode 0Dh & above
   B000:0      MDA RAM, Hercules graphics display RAM
   B800:0      CGA display RAM
   C000:0      EGA/VGA BIOS ROM (thru C7FF)
   C400:0      Video adapter ROM space
   C600:0 256bytes PGA communication area
   C800:0    16K   Hard disk adapter BIOS ROM
   C800:5      XT Hard disk ROM format, AH=Drive, AL=Interleave
   D000:0    32K   Cluster adapter BIOS ROM
   D800:0      PCjr conventionalsoftware cartridge address
   E000:0    64K   Expansion ROM space (hardwired on AT+)
       128K   PS/2 System ROM (thru F000)
   F000:0      System monitor ROM
         PCjr: software cartridge override address
   F400:0      System expansion ROMs
   F600:0      IBM ROM BASIC (AT)
   F800:0      PCjr software cartridge override address
   FC00:0      BIOS ROM
   FF00:0      System ROM
   FFA6:E      ROM graphics character table
   FFFF:0      ROM bootstrap code
   FFFF:5 8 bytes   ROM date (not applicable for all clones)
   FFFF:E   byte   ROM machine id   (see MACHINE ID)