Tech Arsenal 1/Tech Arsenal (Arsenal Computer).ISO/tek-01/help-pc.zip/INTERRUP.TXT

Text File | 1990-11-27 | 232KB | 8,417 lines

@Interrupt Services DOS∙BIOS∙EMS∙Mouse
:int table:interrupt table:exceptions:irq
^Intel Defined CPU Exception Table (see notes)

%Interrupt         Function

    0        Divide by zero
    1        Single step
    2        Non-maskable  (NMI)
    3        Breakpoint
    4        Overflow trap
    5        BOUND range exceeded (186,286,386)
    6        Invalid opcode (186,286,386)
    7        Coprocessor not available (286,386)
    8        Double fault exception (286,386)
    9        Coprocessor segment overrun (286,386)
    A        Invalid task state segment (286,386)
    B        Segment not present (286,386)
    C        Stack exception (286,386)
    D        General protection exception (286,386)
    E        Page fault (286,386)
    F        Reserved
   10        Coprocessor error (286,386)

^IBM PC Hardware Interrupt Table (in order of priority)

%IRQ#  Interrupt         Function

 IRQ0      8     timer (55ms intervals, 18.2 per second)
 IRQ1      9     keyboard service required
 IRQ2      A     slave 8259 or EGA/VGA vertical retrace
 IRQ8     70     real time clock  (AT,XT286,PS50+)
 IRQ9     71     software redirected to IRQ2  (AT,XT286,PS50+)
 IRQ10    72     reserved  (AT,XT286,PS50+)
 IRQ11    73     reserved  (AT,XT286,PS50+)
 IRQ12    74     mouse interrupt  (PS50+)
 IRQ13    75     numeric coprocessor error  (AT,XT286,PS50+)
 IRQ14    76     fixed disk controller (AT,XT286,PS50+)
 IRQ15    77     reserved  (AT,XT286,PS50+)
 IRQ3      B     COM2 service required, (COM3-COM8 on MCA PS2)
 IRQ4      C     COM1 service required
 IRQ5      D     fixed disk or data request from LPT2
 IRQ6      E     floppy disk service required
 IRQ7      F     data request from LPT1 (unreliable on IBM mono)


^Interrupt Table as Implemented by System BIOS/DOS

%INT #    Locus         Function

   0       CPU      divide by zero
   1       CPU      single step
   2       CPU      non-maskable
   3       CPU      breakpoint
   4       CPU      overflow trap
   5       BIOS     print screen
   6       CPU      Invalid opcode (186,286,386)
   7       CPU      coprocessor not available (286,386)
   8       IRQ0     timer (55ms intervals, 18.21590 per second)
   9       IRQ1     keyboard service required (see INT 9)
   A       IRQ2     slave 8259 or EGA/VGA vertical retrace
   B       IRQ3     COM2 service required (PS2 MCA COM3-COM8)
   C       IRQ4     COM1 service required
   D       IRQ5     fixed disk or data request from LPT2
   E       IRQ6     floppy disk service required
   F       IRQ7     data request from LPT1 (unreliable on IBM mono)
  10       BIOS     video (see INT 10)
  11       BIOS     Equipment determination (see INT 11)
  12       BIOS     memory size (see INT 12)
  13       BIOS     disk I/O service  (see INT 13)
  14       BIOS     serial communications (see INT 14)
  15       BIOS     system services, cassette (see INT 15)
  16       BIOS     keyboard services (see INT 16)
  17       BIOS     parallel printer (see INT 17)
  18       BIOS     ROM BASIC loader
  19       BIOS     bootstrap loader (unreliable, see INT 19)
  1A       BIOS     time of day  (see INT 1A)
  1B       BIOS     user defined ctrl-break handler (see INT 1B)
  1C       BIOS     user defined clock tick handler (see INT 1C)
  1D       BIOS     6845 video parameter pointer
  1E       BIOS     diskette parameter pointer (base table)
  1F       BIOS     graphics character table
  20       DOS      general program termination
  21       DOS      function request services (see INT 21)
  22       DOS      terminate address (see INT 22)
  23       DOS      control break termination address (see INT 23)
  24       DOS      critical error handler (see INT 24)
  25       DOS      absolute disk read (see INT 25)
  26       DOS      absolute disk write (see INT 26)
  27       DOS      terminate and stay resident (see INT 27)
  28       DOS      idle loop, issued by DOS when idle (see INT 28)
  29       DOS      fast TTY console I/O (see INT 29)
  2A       DOS      critical section and NETBIOS (see INT 2A)
  2B       DOS      internal
  2C       DOS      internal
  2D       DOS      internal
  2E       DOS      exec command from base level command
                    interpreter  (see INT 2E)
  2F       DOS      multiplexer (see INT 2F)
  30-31    CPM      far jump vector for CPM (not an interrupt)
  32                reserved
  33                mouse support (see INT 33)
  34-3E             Microsoft/Borland floating point emulation
  3F                overlay manager
  40       BIOS     hard disk
  41       BIOS     fixed disk 0 parameters pointer (see INT 13,9)
  42       BIOS     relocated video handler (EGA/VGA/PS)
  43       BIOS     user font table (EGA/VGA/PS)
  44       BIOS     first 128 graphics characters (also Netware)
  45       BIOS     reserved for BIOS
  46       BIOS     fixed disk 1 parameters ptr (see INT 13,9/INT 41)
  47       BIOS     reserved for BIOS
  48       BIOS     PCjr cordless keyboard translation
  49       BIOS     PCjr non-keyboard scancode translation table
  4A       BIOS     user alarm  (AT/CONV/PS2) (see INT 4A)
  4B-4F    BIOS     reserved
  50       BIOS     periodic alarm from timer (PS2)
  51-58    BIOS     reserved
  59       BIOS     GSS Computer Graphics Interface
  5A       BIOS     cluster adapter BIOS entry point
  5B       BIOS     cluster adapter boot
  5C       NETBIOS  NETBIOS interface, TOPS interface
  5D-5F    BIOS     reserved for BIOS
  60-67             reserved for user software interrupts
  67       EMS      LIM/EMS specification (see INT 67)
  68                APPC
  69-6B             reserved by IBM
  6C       DOS      DOS 3.2 real time clock update
           BIOS     system resume vector
  6D-6F             reserved
  70       IRQ8     real time clock  (AT,XT286,PS50+, see INT 15)
  71       IRQ9     software redirected to IRQ2  (AT,XT286,PS50+)
  72       IRQ10    reserved  (AT,XT286,PS50+)
  73       IRQ11    reserved  (AT,XT286,PS50+)
  74       IRQ12    mouse interrupt  (PS50+)
  75       IRQ13    numeric coprocessor NMI error  (AT,XT286,PS50+)
  76       IRQ14    fixed disk controller (AT,XT286,PS50+)
  77       IRQ15    reserved  (AT,XT286,PS50+)
  78-79             unused
  80-85             ROM BASIC
  86-F0    DOS      reserved for BASIC interpreter use
  86       NETBIOS  NETBIOS relocated INT 18h
  E0       CPM      CP/M 86 function calls
  F1-FF             reserved by IBM
  FE-FF             may be destroyed by return from protected
                    mode using VDISK on 286 machines (Apr 86, DDJ)


 - Intel defined 0 through 20h for use for internal CPU;  IBM
   redefined interrupts 0 through 1Fh for its own use, hence
   the duplicate definitions in the tables
 - all interrupts except the internal CPU exceptions push the
   flags and the CS:IP of the next instruction onto the stack.
   CPU exception interrupts are similar but push the CS:IP of the
   causal instruction.   8086/88 divide exceptions are different,
   they return to the instruction following the division
 - interrupts are disabled upon entry into any interrupt routine and
   should be enabled by the user or by an IRET
 - in DOS 3.2+ hardware IRQ interrupts are re-vectored through DOS
   to provide standard stack frames

:int 5
^INT 5 - Print Screen


 no input data


%related memory:

 50:0 = 00  Print screen has not been called, or upon return
            from a call there were no errors
      = 01  Print screen is already in progress
      = FF  Error encountered during printing


 - invoked from INT 9

:int 8:bios timer interrupt
^INT 8 - System timer

 no input data

%related memory:

    40:6C = Daily timer counter (4 bytes)
    40:70 = 24 hr overflow flag (1 byte)
    40:67 = Day counter on all products after AT
    40:40 = Motor shutoff counter - decremented until 0 then
            shuts off diskette motor


 - INT 1C is invoked as a user interrupt
 - the byte at 40:70 is a flag that certain DOS functions use
   and adjust the date if necessary.  Since this is a flag and
   not a counter it results in DOS (not the RTC) losing days
   when several midnights pass before a DOS call
 - generated 18.2 times per second by the 8253 Programmable Interval
   Timer (PIT)
 - normal INT 8 execution takes approximately 100 microseconds

 - see   8253

:int 9:keyboard interrupt
^INT 9 - Keyboard Interrupt (Hardware Handler)

 no input data

%related memory:

 40:17 = updates keyboard flag byte 0
 40:18 = updates keyboard flag byte 1
 40:1A = queue head ptr is set to buffer start if Ctrl-Break is hit
 40:1C = updates buffer tail pointer for each keystroke; sets
         queue tail ptr is set to queue start if Ctrl-Break is hit
 40:1E = updates keyboard buffer (32 bytes)
 40:71 = updates bit 7 of the BIOS break flag if Ctrl-Break is hit
 40:72 = updates reset flag with 1234H if Ctrl-Alt-Del pressed
 40:96 = indicates keyboard type (AT,PS2)
 40:97 = updates keyboard LED flags (AT,PS2)
 FFFF:0 = reboot code called if Ctrl-Alt-Del pressed

%related interrupts:

 INT 05    invoked if print screen key pressed
 INT 1B    invoked if Ctrl-Break key sequence pressed
 INT 15,85 invoked on AT if system request key is pressed
 INT 15,4F invoked on machines after PC/AT with AL = scan code


 - records key press and key release via IRQ1/8259 and
   stores scan codes in the BIOS buffer located at 40:1C
 - keyboard controllers also buffer data when interrupts are
   disabled at the 8259 interrupt controller
 - keyboard controller is capable of storing 16 keystrokes
   even when interrupts are disabled at the 8259
 - normal INT 9 execution takes approximately 500 microseconds;
   at least one standard XT BIOS is known to take up to 1.3
   milliseconds to execute

 - see   MAKE CODES   KB FLAGS

:int 10:bios video services:video interrupt
^INT 10 - Video BIOS Services

%Function requested in AH; see also  INT 10,N  where N is:

     0 - Set video mode
     1 - Set cursor type
     2 - Set cursor position
     3 - Read cursor position
     4 - Read light pen
     5 - Select active display page
     6 - Scroll active page up
     7 - Scroll active page down
     8 - Read character and attribute at cursor
     9 - Write character and attribute at cursor
     A - Write character at current cursor
     B - Set color palette
     C - Write graphics pixel at coordinate
     D - Read graphics pixel at coordinate
     E - Write text in teletype mode
     F - Get current video state
    10 - Set/get palette registers (EGA/VGA)
    11 - Character generator routine (EGA/VGA)
    12 - Video subsystem configuration (EGA/VGA)
    13 - Write string (BIOS after 1/10/86)
    14 - Load LCD char font (convertible)
    15 - Return physical display parms (convertible)
    1A - Video Display Combination (VGA)
    1B - Video BIOS Functionality/State Information (MCGA/VGA)
    1C - Save/Restore Video State  (VGA only)
    FE - Get DESQView/TopView Virtual Screen Regen Buffer
    FF - Update DESQView/TopView Virtual Screen Regen Buffer


 Warning: Some BIOS implementations have a bug that causes
 register BP to be destroyed.   It is advisable to save BP
 before a call to Video BIOS routines on these systems.

 - see  INT 1F   INT 1D   INT 29   INT 21,2   INT 21,6   INT 21,9

:int 10,0:video modes
^INT 10,0 - Set Video Mode

 AH = 00
 AL = 00  40x25 B/W text (CGA,EGA,MCGA,VGA)
    = 01  40x25 16 color text (CGA,EGA,MCGA,VGA)
    = 02  80x25 16 shades of gray text (CGA,EGA,MCGA,VGA)
    = 03  80x25 16 color text (CGA,EGA,MCGA,VGA)
    = 04  320x200 4 color graphics (CGA,EGA,MCGA,VGA)
    = 05  320x200 4 color graphics (CGA,EGA,MCGA,VGA)
    = 06  640x200 B/W graphics (CGA,EGA,MCGA,VGA)
    = 07  80x25 Monochrome text (MDA,HERC,EGA,VGA)
    = 08  160x200 16 color graphics (PCjr)
    = 09  320x200 16 color graphics (PCjr)
    = 0A  640x200 4 color graphics (PCjr)
    = 0B  Reserved (EGA BIOS function 11)
    = 0C  Reserved (EGA BIOS function 11)
    = 0D  320x200 16 color graphics (EGA,VGA)
    = 0E  640x200 16 color graphics (EGA,VGA)
    = 0F  640x350 Monochrome graphics (EGA,VGA)
    = 10  640x350 16 color graphics (EGA or VGA with 128K)
          640x350 4 color graphics (64K EGA)
    = 11  640x480 B/W graphics (MCGA,VGA)
    = 12  640x480 16 color graphics (VGA)
    = 13  320x200 256 color graphics (MCGA,VGA)
    = 8x  EGA, MCGA or VGA ignore bit 7, see below
    = 9x  EGA, MCGA or VGA ignore bit 7, see below


 - if AL bit 7=1, prevents EGA,MCGA & VGA from clearing display
 - function updates byte at 40:49;  bit 7 of byte 40:87
   (EGA/VGA Display Data Area) is set to the value of AL bit 7

:int 10,1
^INT 10,1 - Set Cursor Type


 AH = 01
 CH = cursor starting scan line (cursor top) (low order 5 bits)
 CL = cursor ending scan line (cursor bottom) (low order 5 bits)


 returns nothing


 - cursor lines are zero based
 - monochrome uses starting line 0Bh and ending line 0Ch
 - color uses starting line 6 and ending line 7

:int 10,2
^INT 10,2 - Set Cursor Position


 AH = 02
 BH = page number (0 for graphics modes)
 DH = row
 DL = column


 returns nothing


 - positions relative to 0,0 origin
 - 80x25 mode has coordinates 0,0 to 24,79
 - 40x25 mode has coordinates 0,0 to 24,39
 - see   VIDEO PAGES

:int 10,3
^INT 10,3 - Read Cursor Position and Size


 AH = 03
 BH = video page


 on return:
 CH = cursor starting scan line (low order 5 bits)
 CL = cursor ending scan line (low order 5 bits)
 DH = row
 DL = column


 - returns data from BIOS DATA AREA at location 40:50

:int 10,4
^INT 10,4 - Read Light Pen Position


 AH = 04


 on return:
 AH = 0  light pen switch not triggered
    = 1  light pen triggered
 BX = pixel column (0-319 or 0-639, mode dependent)
 CH = raster line (0-199) (CGA and EGA modes 4, 5 and 6)
 CX = raster line (EGA modes except 4, 5 and 6)
 DH = row (0-24)
 DL = column (0-79 or 0-79 mode dependent)


 - data returned as a byte coordinate, leaving horizontal
   accuracy to within 2 pixels (320) or 4 pixels (640)
 - vertical accuracy within 2 lines
 - PS2's don't support the light pen interface

:int 10,5
^INT 10,5 - Select Active Display Page

 AH = 05
 AL = new page number, see VIDEO PAGES

 for PCjr only:
 AL = 80h to read CRT/CPU page registers
      81h to set CPU page register
          BL = CPU page register
      82h to set CRT page register
          BH = CRT page register
      83h to set CPU and page registers
          BH = CRT page register
          BL = CPU page register


 on return: (PCjr only)
 BH = CRT page register
 BL = CPU page register

 - see   VIDEO PAGES
:int 10,6
^INT 10,6 - Scroll Window Up


 AH = 06
 AL = number of lines to scroll, previous lines are
      blanked, if 0 or AL > screen size, window is blanked
 BH = attribute to be used on blank line
 CH = row of upper left corner of scroll window
 CL = column of upper left corner of scroll window
 DH = row of lower right corner of scroll window
 DL = column of lower right corner of scroll window


 returns nothing


 - in video mode 4 (300x200 4 color) on the EGA, MCGA and VGA
   this function scrolls page 0 regardless of the current page
 - can be used to scroll graphics screens, using character coords
 - on CGA's this function disables video adapter, causing flitter
:int 10,7
^INT 10,7 - Scroll Window Down


 AH = 07
 AL = number of lines to scroll, previous lines are
      blanked, if 0 or AL > screen size, window is blanked
 BH = attribute to be used on blank line
 CH = row of upper left corner of scroll window
 CL = column of upper left corner of scroll window
 DH = row of lower right corner of scroll window
 DL = column of lower right corner of scroll window


 returns nothing


 - in video mode 4 (300x200 4 color) on the EGA, MCGA and VGA
   this function scrolls page 0 regardless of the current page
 - can be used to scroll graphics screens, using character coords
 - on CGA's this function disables video adapter, causing flitter

:int 10,8
^INT 10,8 - Read Character and Attribute at Cursor Position


 AH = 08
 BH = display page


 on return:
 AH = attribute of character (alpha modes only)
 AL = character at cursor position


 - in video mode 4 (300x200 4 color) on the EGA, MCGA and VGA
   this function works only on page zero

:int 10,9
^INT 10,9 - Write Character and Attribute at Cursor Position


 AH = 09
 AL = ASCII character to write
 BH = display page  (or mode 13h, background pixel value)
 BL = character attribute (text) foreground color (graphics)
 CX = count of characters to write (CX >= 1)


 returns nothing


 - does not move the cursor
 - in graphics mode (except mode 13h), if BL bit 7=1 then
   value of BL is XOR'ed with the background color

:int 10,a
^INT 10,A - Write Character Only at Current Cursor Position


 AH = 0A
 AL = ASCII character to write
 BH = display page  (or mode 13h, background pixel value)
 BL = foreground color (graphics mode only)
 CX = count of characters to write (CX >= 1)


 return nothing


 - similar to INT 10,9 except color ignored in text modes

:int 10,b
^INT 10,B - Set Color Palette

 AH = 0B
 BH = palette color ID
    = 0  to set background and border color
    = 1  to select 4 color palette
 BL = color value (when BH = 0)
    = palette value (when BH = 1)

 Palette    Pixel          Color
    0         0      current background color
              1      green (2)
              2      red (4)
              3      brown (6)
    1         0      current background color
              1      cyan (3)
              2      magenta (5)
              3      white (7)

 - does not work for all EGA and VGA video modes
 - sets border color in text mode (BH = 0)

:int 10,c
^INT 10,C - Write Graphics Pixel at Coordinate


 AH = 0C
 AL = color value (XOR'ED with current pixel if bit 7=1)
 BH = page number
 CX = column number (zero based)
 DX = row number (zero based)


 returns nothing


 - if bit 7 is 1, color specified is XOR'ed with current pixel
 - page number in BH ignored for 320x200 4 color graphics mode
 - see   VIDEO PAGES

:int 10,d
^INT 10,D - Read Graphics Pixel at Coordinate


 AH = 0D
 BH = page number
 CX = column number (zero based)
 DX = row number (zero based)


 on return:
 AL = color of pixel read


 - 64K IBM EGAs with BIOS dated 9/13/84 in 350 line video
   modes,  return invalid data in AL
 - page number in BH ignored for 320x200 4 color graphics mode
 - see   VIDEO PAGES

:int 10,e
^INT 10,E - Write Text in Teletype Mode


 AH = 0E
 AL = ASCII character to write
 BH = page number (text modes)
 BL = foreground pixel color (graphics modes)


 returns nothing


 - cursor advances after write
 - characters BEL (7), BS (8), LF (A), and CR (D) are
   treated as control codes
 - for some older BIOS (10/19/81), the BH register must point
   to the currently displayed page
 - on CGA's this function can disable video adapter, causing flitter

:int 10,f
^INT 10,F - Get Video State


 AH = 0F


 on return:
 AH = number of screen columns
 AL = mode currently set (see VIDEO MODES)
 BH = current display page


 - video modes greater than 13h on EGA, MCGA and VGA indicate
   INT 10,0 was called with the high bit of the mode (AL) set
   to 1, meaning the display does not need cleared
 - function returns byte value at 40:49;  On EGA, MCGA and
   VGA bit 7 of register AL is determined by bit 7 of BIOS Data
   Area byte 40:87.   This bit is usually set by INT 10,0
   with bit 7 of the requested mode (in AL) set to 1

:int 10,10
^INT 10,10 - Set/Get Palette Registers (EGA/VGA)

 AH = 10h

%AL = 00  set individual palette register
    BH = color value
    BL = palette register


%AL = 01  set border color (overscan register)
    BH = color value


%AL = 02  set all palette registers and border
    ES:DX = pointer to 17 byte table representing 16 palette
            registers and border color register


%AL = 03  toggle intensity/blinking (EGA)
    BL = 0  enable intensity
         1  enable blinking


%AL = 07  read palette register (PS2)
    BL = palette register to read (0-15)

 on return:
   BH = value of palette register


%AL = 08  read border color (overscan register, PS2)

 on return:
   BH = value of border color (overscan register)


%AL = 09  read palette registers and border (PS2)
    ES:DX = pointer to 17 byte table representing 16 palette
            registers and border color register

 on return:
 ES:DX = pointer to table provided as input


%AL = 10  set DAC color register
    BX = color register to set
    CH = green value
    CL = blue value
    DH = red value


%AL = 12  set block of DAC color registers
    BX = first color register to set
    CX = number of color registers to set
    ES:DX = pointer to table of color values to set


%AL = 13  set attribute controller color select state
    BL = 0  set Mode Control register bit 7
       BH = value for bit 7
    BL = 1  set color select register
       BH = value for color select register


%AL = 15  read DAC color register (PS2)
    BX = color register to read

 on return:
 CH = green value
 CL = blue value
 DH = red value


%AL = 17  read block of DAC color registers
    BX = first color register to read
    CX = number of color registers to read
    ES:DX = pointer to buffer for color registers

 on return:
 ES:DX = pointer to color table provided as input


%AL = 18  update video DAC mask register
    BL = new mask


%AL = 19  read video DAC mask register

 on return:
 BL = value read from video DAC mask register


%AL = 1A  read color page state
    BL = bit 7 of Mode Control Register
    BH = bits 2 thru 3 of Color select register if BL = 0
       = bits 0 thru 3 of Color select register if BL = 1

 on return:
 BL = current paging mode
 CX = current page



%AL = 1B  sum color values to shades of gray
    BX = first color register to sum
    CX = number of color registers to sum


 - controls the pixel color mapping bit values
 - BIOS extension to EGA/VGA systems

:int 10,11
^INT 10,11 - Character Generator Routine (EGA/VGA)

 AH = 11h

%AL = 00  user character load
    BH = number of bytes per character
    BL = table in character generator RAM
    CX = count of characters in table
    DX = ASCII code of first character defined
    ES:BP = pointer to user table


%AL = 01  ROM BIOS 8x14 monochrome set
    BL = table in character generator RAM


%AL = 02  ROM BIOS 8x8 double dot
    BL = table in character generator RAM


%AL = 03  set displayed definition table
    BL = value for character Map Select register (EGA,VGA)
       = character generator RAM table numbers (MCGA)


%AL = 04  ROM BIOS 8x16 character set
    BL = table in character generator RAM


%AL = 10  user specified character definition table
    BH = bytes per character (points)
    BL = table in character generator RAM
    CX = number of characters defined in table
    DX = ASCII code of first character defined
    ES:BP = pointer to user table


%AL = 11  ROM BIOS 8x14 monochrome character set
    BL = table in character generator RAM


%AL = 12  ROM 8x8 double dot character definitions
    BL = table in character generator RAM


%AL = 14  ROM 8x16 double dot character definitions
    BL = table in character generator RAM


%AL = 20  pointer to graphics character table for INT 1F (8x8)
    ES:BP = pointer to user table


%AL = 21  user graphics character pointer at INT 43
    BL = row specifier
       = 0 - user specified  (DL = rows)
       = 1 is 14 rows
       = 2 is 25 rows
       = 3 is 43 rows
    CX = bytes per character (points)
    DL = rows (when BL = 0)
    ES:BP = pointer to user table


%AL = 22  ROM 8x14 character set
    BL = number of rows (see AL=21)
    DL = rows (when BL = 0)


%AL = 23  ROM 8x8 double dot character set
    BL = row specifier (see AL=21)
    DL = rows (when BL = 0)


%AL = 24  ROM 8x16 character set
    BL = row specifier (see AL=21)
    DL = rows (when BL = 0)


%AL = 30  get current character generator information
    BH = information desired:
       = 0  INT 1F pointer
       = 1  INT 44h pointer
       = 2  ROM 8x14 pointer
       = 3  ROM 8x8 double dot pointer (base)
       = 4  ROM 8x8 double dot pointer (top)
       = 5  ROM 9x14 alpha alternate pointer
       = 6  ROM 8x16 character table pointer
       = 7  ROM 9x16 alternate character table pointer

 on return:
 CX = bytes per character (points)
 DL = rows (less 1)
 ES:BP = pointer to table

:int 10,12
^INT 10,12 - Video Subsystem Configuration (EGA/VGA)

 AH = 12h


%BL = 10  return video configuration information

 on return:
 BH = 0 if color mode in effect
    = 1 if mono mode in effect
 BL = 0 if 64k EGA memory
    = 1 if 128k EGA memory
    = 2 if 192k EGA memory
    = 3 if 256k EGA memory
 CH = feature bits
 CL = switch settings


%BL = 20  select alternate print screen routine

%BL = 30  select scan lines for alphanumeric modes
    AL = 0  200 scan lines
       = 1  350 scan lines
       = 2  400 scan lines

 on return:
 AL = 12


%BL = 31  select default palette loading
    AL = 0 enable default palette loading
       = 1 disable default palette loading

 on return:
 AL = 12


%BL = 32  CPU access to video RAM
    AL = 0  enable CPU access to video RAM and I/O ports
       = 1  disable CPU access to video RAM and I/O ports

 on return:
 AL = 12


%BL = 33  Gray scale summing
    AL = 0  enable gray scale summing
       = 2  disable gray scale summing

 on return:
 AL = 12


%BL = 34  cursor emulation
    AL = 0  enable cursor emulation
       = 1  disable cursor emulation

 on return:
 AL = 12


%BL = 35  PS2 video display switching
    AL = 0 initial adapter video off
       = 1 initial planar video on
       = 2 switch active video off
       = 3 switch inactive video on
    ES:DX pointer to 128 byte save area (when AL = 0, 2 or 3)

 on return:
 AL = 12


%BL = 36  video refresh control
    AL = 0 enable refresh
       = 1 disable refresh

 on return:
 AL = 12

:int 10,13
^INT 10,13 - Write String (BIOS versions from 1/10/86)

 AH = 13h
 AL = write mode (see bit settings below)
    = 0 string is chars only, attribute in BL, cursor not moved
    = 1 string is chard only, attribute in BL, cursor moved
    = 2 string contains chars and attributes, cursor not moved
    = 3 string contains chars and attributes, cursor moved
 BH = video page number
 BL = attribute if mode 0 or 1 (AL bit 1=0)
 CX = length of string (ignoring attributes)
 DH = row coordinate
 DL = column coordinate
 ES:BP = pointer to string


 Bit settings for write mode (register AL):

 │7│6│5│4│3│2│1│0│  AL
  │ │ │ │ │ │ │ └──── 0=don't move cursor, 1=move cursor
  │ │ │ │ │ │ └───── 0=BL has attributes, 1=string has attributes
  └─┴─┴─┴─┴─┴────── unused


 returns nothing


 - BEL, BS, CR, LF are treated as ASCII control codes
 - wraps data and scrolls if unable to fit data on one line

:int 10,14
^INT 10,14 - Load LCD Character Font (convertible only)

 AH = 14h

%AL = 0 - load user specified font
    ES:DI = pointer to character font
    CX = number of characters to store
    DX = char offset into ram font area
    BH = number of bytes per character
    BL = 0  load main font (block 0)
       = 1  load alternate font (block 1)

%AL = 1 - load system ROM default font
    BL = 0  load main font (block 0)
       = 1  load alternate font (block 1)

%AL = 2 - set mapping of LCD high intensity attribute
    BL = 0  ignore high intensity attribute
       = 1  map high intensity to underscore
       = 2  map high intensity to reverse video
       = 3  map high intensity to select alternate font
:int 10,15
^INT 10,15 - Return Physical Display Parms (convertible)


 AH = 15h

 on return:
 AX = alternate display adapter type
 ES:DI = pointer to parameter table:


%Offset Size       Description

   01   word   monitor model number
   02   word   vertical pels per meter
   03   word   horizontal pels per meter
   04   word   total number of vertical pels
   05   word   total number of horizontal pels
   06   word   horizontal pel separation in micrometers
   07   word   vertical pel separation in micrometers

:int 10,1a
^INT 10,1A - Video Display Combination (VGA)

 AH = 1A
 AL = 00 get video display combination
    = 01 set video display combination
      BL = active display  (see table below)
      BH = inactive display


 on return:
 AL = 1A, if a valid function was requested in AH
 BL = active display  (AL=00, see table below)
 BH = inactive display  (AL=00)

%Valid display codes:

  FF  Unrecognized video system
  00  No display
  01  MDA with monochrome display
  02  CGA with color display
  03  Reserved
  04  EGA with color display
  05  EGA with monochrome display
  06  Professional graphics controller
  07  VGA with analog monochrome display
  08  VGA with analog color display
  09  Reserved
  0A  MCGA with digital color display
  0B  MCGA with analog monochrome display
  0C  MCGA with analog color display

 - returns value at byte 40:8A indicating display combination status
 - used to detect video display capabilities

:int 10,1b
^INT 10,1B - Video BIOS Functionality and
^State Information (MCGA/VGA)

 AH = 1B
 BX = implementation type (must be zero)
 ES:DI = pointer to 64 byte buffer


 on return:
 AL = 1B
 ES:DI = pointer to updated buffer  (see below)


 - returns static and dynamic information about the current
   state and capabilities of the current video system
 - bytes 0-3 of the dynamic data table at ES:DI contain a far
   pointer to the video static information table


^Video BIOS Dynamic Functionality State Table (MCGA/VGA)

%Dynamic Video State Table

 00  dword   address of static functionality table
 04  byte    video mode
 05  word    number of columns
 07  word    length of displayed video buffer (# bytes)
 09  word    start address of upper left corner of video buffer
 0B  16bytes cursor position table for 8 pages (col,row)
 1B  byte    cursor end line
 1C  byte    cursor start line
 1D  byte    active video page
 1E  word    I/O port for CRTC address register
 20  byte    current value of CRTC 3x8 register
 21  byte    current value of CRTC 3x9 register
 22  byte    number of displayed character rows
 23  word    height of character matrix (points)
 25  byte    active display combination code
 26  byte    inactive display combination code
 27  word    number of displayed colors (mono = 0)
 29  byte    number of supported video pages
 2A  byte    raster scan lines 0=200, 1=350, 2=400, 3=480
 2B  byte    text character table used
 2C  byte    text character table used
 2D  byte    other state information:

    │7│6│5│4│3│2│1│0│ State Information byte at offset 2D
     │ │ │ │ │ │ │ └─── 1 = all modes active (MCGA always 0)
     │ │ │ │ │ │ └──── 1 = gray scale summing enabled
     │ │ │ │ │ └───── 1 = monochrome display attached
     │ │ │ │ └────── 1 = default palette loading disabled
     │ │ │ └─────── 1 = cursor emulation enabled
     │ │ └──────── 1 = blinking attribute enabled
     └─┴───────── 1 = reserved

 2E 3bytes   reserved
 31  byte    video RAM available 0=64K, 1=128K, 2=192K, 3=256K
 32  byte    save area status

    │7│6│5│4│3│2│1│0│ Save Area Status
     │ │ │ │ │ │ │ └─── 1 = two text char sets are active
     │ │ │ │ │ │ └──── 1 = dynamic save area is active
     │ │ │ │ │ └───── 1 = text char set override is active
     │ │ │ │ └────── 1 = graphics char set is override active
     │ │ │ └─────── 1 = palette override is active
     │ │ └──────── 1 = display combination code ext. active
     └─┴───────── 1 = reserved

 33  dword   reserved


^Video BIOS Static Functionality Table  (EGA/VGA)

 │7│6│5│4│3│2│1│0│ Video modes supported, byte at offset 00
  │ │ │ │ │ │ │ └─── 1 = mode 0
  │ │ │ │ │ │ └──── 1 = mode 1
  │ │ │ │ │ └───── 1 = mode 2
  │ │ │ │ └────── 1 = mode 3
  │ │ │ └─────── 1 = mode 4
  │ │ └──────── 1 = mode 5
  │ └───────── 1 = mode 6
  └────────── 1 = mode 7

 │7│6│5│4│3│2│1│0│ Video modes supported, byte at offset 01
  │ │ │ │ │ │ │ └─── 1 = mode 8
  │ │ │ │ │ │ └──── 1 = mode 9
  │ │ │ │ │ └───── 1 = mode A
  │ │ │ │ └────── 1 = mode B
  │ │ │ └─────── 1 = mode C
  │ │ └──────── 1 = mode D
  │ └───────── 1 = mode E
  └────────── 1 = mode F

 │7│6│5│4│3│2│1│0│ Video modes supported, byte at offset 02
  │ │ │ │ │ │ │ └─── 1 = mode 10
  │ │ │ │ │ │ └──── 1 = mode 11
  │ │ │ │ │ └───── 1 = mode 12
  │ │ │ │ └────── 1 = mode 13
  └─┴─┴─┴─────── reserved

 03  dword  reserved
 07  byte   scan lines supported in text modes

 │7│6│5│4│3│2│1│0│ Scan lines supported, byte at offset 07
  │ │ │ │ │ │ │ └─── 1 = 200 lines
  │ │ │ │ │ │ └──── 1 = 350 lines
  └─┴─┴─┴─┴─┴───── 1 = 400 lines

 08  byte   max number of displayable text character sets
 09  byte   # of text definition tables in char generator RAM
 0A  byte   other capability flags

     │7│6│5│4│3│2│1│0│ Other flags, byte at offset 0A
      │ │ │ │ │ │ │ └─── 1 = all modes (0 on MCGA)
      │ │ │ │ │ │ └──── 1 = gray scale summing
      │ │ │ │ │ └───── 1 = character set loading
      │ │ │ │ └────── 1 = default palette loading
      │ │ │ └─────── 1 = cursor emulation
      │ │ └──────── 1 = 64 color palette
      │ └───────── 1 = video DAC loading
      └────────── 1 = DAC controlled by ACCS

 0B  byte   other capability flags

     │7│6│5│4│3│2│1│0│ Other flags, byte at offset 0B
      │ │ │ │ │ │ │ └─── 1 = light pen support
      │ │ │ │ │ │ └──── 1 = save/restore video state
      │ │ │ │ │ └───── 1 = blinking/background intensity
      │ │ │ │ └────── 1 = display combination code
      └─┴─┴─┴─────── reserved

 0C  word   reserved
 0E  byte   save area capabilities

     │7│6│5│4│3│2│1│0│  save area capabilities, byte at offset 0E
      │ │ │ │ │ │ │ └──── 1 = multiple text character sets
      │ │ │ │ │ │ └───── 1 = dynamic save area
      │ │ │ │ │ └────── 1 = text character set override
      │ │ │ │ └─────── 1 = graphics character set override
      │ │ │ └──────── 1 = palette override
      │ │ └───────── 1 = display combination code extension
      └─┴────────── reserved

 0F  byte    reserved
:int 10,1c
^INT 10,1C - Save/Restore Video State  (VGA only)

 AH = 1C

%AL = 0  get save buffer size
    CX = requested states
         bit 0: video hardware state
         bit 1: video BIOS data areas
         bit 2: video DAC state

 on return:
 AL = 1C
 BX = buffer size in 64 byte blocks

%AL = 1  save requested state
    CX = requested states (see AL = 0)
    ES:BX = pointer to buffer

 returns nothing

%AL = 2  restore requested states
    CX = requested states (see AL = 0)
    ES:BX = pointer to buffer

 returns nothing

:int 10,fe
^INT 10,FE - Get DESQView/TopView Virtual Screen Regen Buffer


 AH = FE
 ES:DI = set to sentinel value (test for INT 10,FE supported)


 returns:
 ES:DI = address of DESQView/TopView video buffer, DI will always
         be zero


 - on return ES:DI should be tested against the original value;
   the value will change if this function is supported (DESQView
   or TopView loaded), otherwise it will remain unchanged
 - if ES:DI changes this address can be used as the video screen
   regen buffer

:int 10,ff
^INT 10,FF - Update DESQView/TopView Virtual Screen Regen Buffer


 AH = FF
 CX = number of characters changed
 ES:DI = pointer to first character in buffer to change,  ES is
         set to segment returned by INT 10,FE


 returns nothing


 - the physical screen does not get updated until INT 10,FF is
   called in TopView
 - it is not necessary to make this call under DESQView since it
   handles updates automatically
 - calling this function under DESQView will cancel the automatic
   update mode

:int 11:equipment flags
^INT 11 - BIOS Equipment Determination / BIOS Equipment Flags

 no input data

 on return:
 AX contains the following bit flags:

 │F│E│D│C│B│A│9│8│7│6│5│4│3│2│1│0│  AX
  │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ └──── IPL diskette installed
  │ │ │ │ │ │ │ │ │ │ │ │ │ │ └───── math coprocessor
  │ │ │ │ │ │ │ │ │ │ │ │ └─┴────── old PC system board RAM < 256K
  │ │ │ │ │ │ │ │ │ │ │ │ │ └───── pointing device installed (PS2)
  │ │ │ │ │ │ │ │ │ │ │ │ └────── not used on PS2
  │ │ │ │ │ │ │ │ │ │ └─┴─────── initial video mode
  │ │ │ │ │ │ │ │ └─┴────────── # of diskette drives, less 1
  │ │ │ │ │ │ │ └───────────── 0 if DMA installed
  │ │ │ │ └─┴─┴────────────── number of serial ports
  │ │ │ └─────────────────── game adapter installed
  │ │ └──────────────────── unused, internal modem (PS2)
  └─┴───────────────────── number of printer ports


 - bits 3 & 2,  system board RAM if less than 256K motherboard
     00 - 16K                 01 - 32K
     10 - 16K                 11 - 64K (normal)

 - bits 5 & 4,  initial video mode
     00 - unused              01 - 40x25 color
     10 - 80x25 color         11 - 80x25 monochrome


 - bits 7 & 6,  number of disk drives attached, when bit 0=1
     00 - 1 drive             01 - 2 drives
     10 - 3 drive             11 - 4 drives


 - returns data stored at BIOS data location 40:10
 - some flags are not guaranteed to be correct on all machines
 - bit 13 is used on the PCjr to indicate serial printer

:int 12
^INT 12 - Memory Size Determination


 no input data


 on return:
 AX  = the number of contiguous 1k memory blocks found at startup

 - contiguous memory does not include video memory or extended RAM

:int 13:bios disk services
^INT 13 - Diskette BIOS Services

%Function requested in AH; see also  INT 13,N  where N is:

     0 - Reset disk system
     1 - Get disk status
     2 - Read disk sectors
     3 - Write disk sectors
     4 - Verify disk sectors
     5 - Format disk track
     6 - Format track and set bad sector flag (XT & portable)
     7 - Format the drive starting at track (XT & portable)
     8 - Get current drive parameters (XT & newer, see note ╪)
     9 - Initialize 2 fixed disk base tables (XT & newer, see note ╪)
     A - Read long sector (XT & newer, see note ╪)
     B - Write long sector (XT & newer, see note ╪)
     C - Seek to cylinder (XT & newer, see note ╪)
     D - Alternate disk reset (XT & newer, see note ╪)
     E - Read sector buffer (XT & portable only)
     F - Write sector buffer (XT & portable only)
    10 - Test for drive ready (XT & newer, see note ╪)
    11 - Recalibrate drive (XT & newer, see note ╪)
    12 - Controller ram diagnostic (XT & portable only)
    13 - Drive diagnostic (XT & portable only)
    14 - Controller internal diagnostic (XT & newer, see note ╪)
    15 - Read disk type/DASD type (XT BIOS from 1/10/86 & newer)
    16 - Disk change line status (XT BIOS from 1/10/86 & newer)
    17 - Set dasd type for format (XT BIOS from 1/10/86 & newer)
    18 - Set media type for format (BIOS date specific)
    19 - Park fixed disk heads (AT & newer)
    1A - Format ESDI drive unit (PS2 50+)


 ╪  The 1983 version of the "IBM XT BIOS Technical Reference"
    shows these functions are available for the XT but many other
    programming references say they aren't available until the AT.
    This is probably due to misunderstanding the design of the disk
    BIOS.   Upon bootup the hard disk BIOS replaces the default
    INT 13h diskette handler with the hard disk INT 13h handler.


%Most disk BIOS calls use the following parameter scheme:

     AH = function request number
     AL = number of sectors  (1-128 dec.)
     CH = cylinder number  (0-1023 dec.)
     CL = sector number  (1-17 dec.)
     DH = head number  (0-15 dec.)
     DL = drive number (0=A:, 1=2nd floppy, 80h=drive 0, 81h=drive 1)
     DL = drive number (0=A:, 1=2nd floppy, 80h=C:, 81h=D:)
          Note that some programming references use (0-3) as the
          drive number which represents diskettes only.
     ES:BX = address of user buffer


%and return with:
 CF = 0 if successful
    = 1 if error
 AH = status of operation  (see INT 13,STATUS)


 - INT 13 diskette read functions should be retried at least 3
   times to assure the disk motor has time to spin up to speed
 - physical sector numbers can be converted to and from DOS sector
   numbers with the following formulas:

   dos_sector = (sector - 1) + (head * sectors_per_track) +
                (track * sectors_per_track * num_heads)

   physical_sector = 1 + (dos_sector  MOD  sectors_per_track)
   physical_head = (dos_sector / sectors_per_track)  MOD  num_heads
   physical_track = dos_sector / (sectors_per_track * num_heads)

 - see  INT 13,n  where n is the function code
 - see  INT 13,STATUS

:int 13,0
^INT 13,0 - Reset Disk System


 AH = 00
 DL = drive number (0=A:, 1=2nd floppy, 80h=drive 0, 81h=drive 1)


 on return:
 AH = disk operation status  (see INT 13,STATUS)
 CF = 0 if successful
    = 1 if error


 - clears reset flag in controller and pulls heads to track 0
 - setting the controller reset flag causes the disk to recalibrate
   on the next disk operation
 - if bit 7 is set, the diskette drive indicated by the lower 7 bits
   will reset then the hard disk will follow; return code in AH is
   for the drive requested

:int 13,1:int 13,status
^INT 13,1 - Disk Status

 AH = 01

 on return:
 AL = status:

%Status in AL

    00  no error
    01  bad command passed to driver
    02  address mark not found or bad sector
    03  diskette write protect error
    04  sector not found
    05  fixed disk reset failed
    06  diskette changed or removed
    07  bad fixed disk parameter table
    08  DMA overrun
    09  DMA access across 64k boundary
    0A  bad fixed disk sector flag
    0B  bad fixed disk cylinder
    0C  unsupported track/invalid media
    0D  invalid number of sectors on fixed disk format
    0E  fixed disk controlled data address mark detected
    0F  fixed disk DMA arbitration level out of range
    10  ECC/CRC error on disk read
    11  recoverable fixed disk data error, data fixed by ECC
    20  controller error (NEC for floppies)
    40  seek failure
    80  time out, drive not ready
    AA  fixed disk drive not ready
    BB  fixed disk undefined error
    CC  fixed disk write fault on selected drive
    E0  fixed disk status error/Error reg = 0
    FF  sense operation failed


 - codes represent controller status after last disk operation
 - returns the status byte located at 40:41 in the BIOS Data Area

:int 13,2
^INT 13,2 - Read Disk Sectors

 AH = 02
 AL = number of sectors to read  (1-128 dec.)
 CH = track/cylinder number  (0-1023 dec., see below)
 CL = sector number  (1-17 dec.)
 DH = head number  (0-15 dec.)
 DL = drive number (0=A:, 1=2nd floppy, 80h=drive 0, 81h=drive 1)
 ES:BX = pointer to buffer


 on return:
 AH = status  (see INT 13,STATUS)
 AL = number of sectors read
 CF = 0 if successful
    = 1 if error


 - BIOS disk reads should be retried at least three times and the
   controller should be reset upon error detection
 - be sure ES:BX does not cross a 64K segment boundary or a
   DMA boundary error will occur
 - many programming references list only floppy disk register values
 - only the disk number is checked for validity
 - the parameters in CX change depending on the number of cylinders;
   the track/cylinder number is a 10 bit value taken from the 2 high
   order bits of CL and the 8 bits in CH (low order 8 bits of track):

   │F│E│D│C│B│A│9│8│7│6│5-0│  CX
    │ │ │ │ │ │ │ │ │ │  └─────  sector number
    │ │ │ │ │ │ │ │ └─┴───────  high order 2 bits of track/cylinder
    └─┴─┴─┴─┴─┴─┴─┴──────────  low order 8 bits of track/cyl number

 - see   INT 13,STATUS   INT 13,A

:int 13,3
^INT 13,3 - Write Disk Sectors

 AH = 03
 AL = number of sectors to write  (1-128 dec.)
 CH = track/cylinder number  (0-1023 dec.)
 CL = sector number  (1-17 dec., see below)
 DH = head number  (0-15 dec.)
 DL = drive number (0=A:, 1=2nd floppy, 80h=drive 0, 81h=drive 1)
 ES:BX = pointer to buffer


 on return:
 AH = 0 if CF=0; otherwise disk status  (see INT 13,STATUS)
 AL = number of sectors written
 CF = 0 if successful
    = 1 if error


 - BIOS disk write attempts should reset the controller on error
 - be sure ES:BX does not cross a 64K segment boundary or a
   DMA boundary error will occur
 - IBM PC XT 286 does not require a value in AL, though it is
   recommended that one be supplied for portability
 - many programming references list only floppy disk register values
 - only the disk number is checked for validity
 - the parameters in CX change depending on the number of cylinders;
   the track/cylinder number is a 10 bit value taken from the 2 high
   order bits of CL and the 8 bits in CH (low order 8 bits of track):

   │F│E│D│C│B│A│9│8│7│6│5-0│  CX
    │ │ │ │ │ │ │ │ │ │  └─────  sector number
    │ │ │ │ │ │ │ │ └─┴───────  high order 2 bits of track/cylinder
    └─┴─┴─┴─┴─┴─┴─┴──────────  low order 8 bits of track/cyl number

 - see   INT 13,STATUS   INT 13,B

:int 13,4
^INT 13,4 - Verify Disk Sectors

 AH = 04
 AL = number of sectors to verify  (1-128 dec.)
 CH = track/cylinder number  (0-1023 dec., see below)
 CL = sector number  (1-17 dec.)
 DH = head number  (0-15 dec.)
 DL = drive number (0=A:, 1=2nd floppy, 80h=drive 0, 81h=drive 1)
 ES:BX = pointer to buffer

 on return:
 AH = status  (see INT 13,STATUS)
 AL = number of sectors verified
 CF = 0 if successful
    = 1 if error


 - BIOS disk reads should be retried at least three times and the
   controller should be reset upon error detection
 - causes controller to calculate the CRC of the disk data and
   compare it against the CRC stored in the sector header
 - BIOS before 11/15/85 required ES:BX point to a valid buffer
   that doesn't cross DMA boundaries.   More recent BIOS versions
   actually ignore the buffer and the DMA boundary requirement
 - use this function to check for valid formatted diskette in a
   the specified drive and for drive ready for read
 - only the disk number is checked for validity
 - the parameters in CX change depending on the number of cylinders;
   the track/cylinder number is a 10 bit value taken from the 2 high
   order bits of CL and the 8 bits in CH (low order 8 bits of track):

   │F│E│D│C│B│A│9│8│7│6│5-0│  CX
    │ │ │ │ │ │ │ │ │ │  └─────  sector number
    │ │ │ │ │ │ │ │ └─┴───────  high order 2 bits of track/cylinder
    └─┴─┴─┴─┴─┴─┴─┴──────────  low order 8 bits of track/cyl number

 - see   INT 13,STATUS   DETECTING

:int 13,5
^INT 13,5 - Format Disk Track

 AH = 05
 AL = interleave value (XT only)
 CX = track/cylinder number (see below for format)
 DH = head number  (0-15 dec.)
 DL = drive number (0=A:, 1=2nd floppy, 80h=drive 0, 81h=drive 1)
 ES:BX = pointer to block of "track address fields" containing
         four byte fields for each sector to be formatted of the form:

        1 byte  track number
        1 byte  head number           Size      #
        1 byte  sector number         Codes   Bytes
        1 byte  sector size code        0      128
                                        1      256
                                        2      512
                                        3     1024
 on return:
 AH = status  (see INT 13,STATUS)
 CF = 0 if successful
    = 1 if error


 - BIOS disk write attempts should reset the controller on error
 - INT 13,17 should be called to set the DASD type
 - this function is capable of doing great damage if the parameters
   are incorrectly specified; only the drive number is checked
 - initializes disk address fields and data sectors
 - interleave is specified by ordering of track address fields
 - after INT 13 disk format, if the disk is to be used with DOS the
   DOS data structure must be written
 - only the disk number is checked for validity
 - the parameters in CX change depending on the number of cylinders;
   the track/cylinder number is a 10 bit value taken from the 2 high
   order bits of CL and the 8 bits in CH (low order 8 bits of track):

    │F│E│D│C│B│A│9│8│7│6│5-0│  CX (cylinder value 0-1023 dec.)
     │ │ │ │ │ │ │ │ │ │  └─────  unused
     │ │ │ │ │ │ │ │ └─┴───────  high order 2 bits of track/cylinder
     └─┴─┴─┴─┴─┴─┴─┴──────────  low order 8 bits of track/cyl number

 - see   INT 13,STATUS   INT 13,17

:int 13,6
^INT 13,6 - Format Track and Set Bad Sector Flags (XT & portable)

 AH = 06
 AL = Interleave value (XT only)
 BX = format buffer, size = 512 bytes;  the first
      2*(sectors/track) bytes contain F,N for each sector
      F = 00h for good sector,
      F = 80h for bad sector
      N = sector number


 on return:
 AH = status  (see INT 13,STATUS)
 CF = 0 if successful
    = 1 if error


 - BIOS disk write attempts should reset the controller on error
 - only the disk number is checked for validity

 - see   INT 13,STATUS
:int 13,7
^INT 13,7 - Format Drive Starting at Specified Track (XT & portable)

 AH = 07
 AL = interleave value (XT only)
 BX = format buffer, size = 512 bytes;  the first 2*(sectors/track)
      bytes contain F, N for each sector where:

         F = 00h for good sector
         F = 80h for bad sector
         N = sector number

 on return:
 AH = status  (see INT 13,STATUS)
 CF = 0 if successful
    = 1 if error


 - BIOS disk write attempts should reset the controller on error
 - only the disk number is checked for validity

 - see   INT 13,STATUS
:int 13,8
^INT 13,8 - Get Current Drive Parameters (XT & newer)

 AH = 08
 DL = drive number (0=A:, 1=2nd floppy, 80h=drive 0, 81h=drive 1)


 on return:
 AH = status  (see INT 13,STATUS)
 BL = CMOS drive type
      01 - 5¼  360K           03 - 3½  720K
      02 - 5¼  1.2Mb          04 - 3½ 1.44Mb
 CH = cylinders (0-1023 dec. see below)
 CL = sectors per track  (see below)
 DH = number of sides (0 based)
 DL = number of drives attached
 ES:DI = pointer to 11 byte Disk Base Table (DBT)
 CF = 0 if successful
    = 1 if error


%Cylinder and Sectors Per Track Format

 │F│E│D│C│B│A│9│8│7│6│5│4│3│2│1│0│  CX
  │ │ │ │ │ │ │ │ │ │ └─┴─┴─┴─┴─┴──  sectors per track
  │ │ │ │ │ │ │ │ └─┴──────────  high order 2 bits of cylinder count
  └─┴─┴─┴─┴─┴─┴─┴──────────  low order 8 bits of cylinder count

 - the track/cylinder number is a 10 bit value taken from the 2 high
   order bits of CL and the 8 bits in CH (low order 8 bits of track)
 - many good programming references indicate this function is only
   available on the AT, PS2 and later systems, but all hard disk
   systems since the XT have this function available
 - only the disk number is checked for validity

 - see   INT 13,STATUS   DBT

:int 13,9
^INT 13,9 - Initialize Fixed Disk Table (XT & newer)

 AH = 09
 DL = fixed disk number  (80h=drive 0, 81h=drive 1)


 on return:
 AH = status  (see INT 13,STATUS)
 CF = 0 if successful
    = 1 if error


 - sets specified fixed disk table to the default values from ROM
 - many good programming references indicate this function is only
   available on the AT, PS2 and later systems, but all hard disk
   systems since the XT have this function available
 - int 41h vector is pointer to table for drive 0
 - int 46h vector is pointer to table for drive 1


^Table  definitions located by interrupt vectors  41H & 46H

%Offset Size         Description

   00   word  maximum number of cylinders
   02   byte  maximum number of heads
   03   word  starting reduced write current cylinder
   05   word  starting write pre-comp cylinder
   07   byte  maximum ECC data burst length
   08   byte  control byte:


   │7│6│5│4│3│2│1│0│  Control byte
    │ │ │ │ │ └─┴─┴──── drive option
    │ │ └─┴─┴───────── always zero
    │ └────────────── disable ECC retries
    └─────────────── disable access retires


 - see    INT 13,STATUS

:int 13,a
^INT 13,A - Read Long Sector (XT & newer)

 AH = 0A
 AL = number of sectors  (1-121 dec.)
 CH = track number  (0-1023 dec., see below)
 CL = sector number  (1-17 dec., see below)
 DH = head number  (0-15 dec.)
 DL = fixed drive number  (80h=drive 0, 81h=drive 1)
 ES:BX = address of buffer


 on return:
 AH = status  (see INT 13,STATUS)
 AL = number of sectors actually transferred
 CF = 0 if successful
    = 1 if error


 - BIOS disk reads should be retried at least three times and the
   controller should be reset upon error detection
 - many good programming references indicate this function is only
   available on the AT, PS2 and later systems, but all hard disk
   systems since the XT have this function available
 - reads regular data sectors (128-1024 bytes) with an additional
   4 byte ECC code included
 - a DMA boundary error will occur if the buffer at ES:BX crosses
   a 64K segment boundary
 - only the disk number is checked for validity
 - the parameters in CX change depending on the number of cylinders;
   the track/cylinder number is a 10 bit value taken from the 2 high
   order bits of CL and the 8 bits in CH (low order 8 bits of track):

   │F│E│D│C│B│A│9│8│7│6│5│4│3│2│1│0│  CX
    │ │ │ │ │ │ │ │ │ │ └─┴─┴─┴─┴─┴────  sector number
    │ │ │ │ │ │ │ │ └─┴────────────  high order 2 bits of track number
    └─┴─┴─┴─┴─┴─┴─┴────────────  low order 8 bits of track number

 - see   INT 13,STATUS   INT 13,2

:int 13,b
^INT 13,B - Write Long Sectors (XT & newer)

 AH = 0B
 AL = number of sectors  (1-121 dec.)
 CH = track number  (0-1023 dec., see below)
 CL = sector number  (1-17 dec., see below)
 DH = head number  (0-15 dec.)
 DL = fixed drive number  (80h=drive 0, 81h=drive 1)
 ES:BX = address of buffer


 on return:
 AL = number of sectors actually transferred
 AH = status  (see INT 13,STATUS)
 CF = 0 if successful
    = 1 if error


 - BIOS disk write attempts should reset the controller on error
 - many good programming references indicate this function is only
   available on the AT, PS2 and later systems, but all hard disk
   systems since the XT have this function available
 - writes regular sectors (128-1024 bytes) with additional 4 byte
   ECC code included in data
 - a DMA boundary error will occur if the buffer at ES:BX crosses
   a 64K segment boundary
 - only the disk number is checked for validity
 - the parameters in CX change depending on the number of cylinders;
   the track/cylinder number is a 10 bit value taken from the 2 high
   order bits of CL and the 8 bits in CH (low order 8 bits of track):

   │F│E│D│C│B│A│9│8│7│6│5│4│3│2│1│0│  CX
    │ │ │ │ │ │ │ │ │ │ └─┴─┴─┴─┴─┴────  sector number
    │ │ │ │ │ │ │ │ └─┴────────────  high order 2 bits of track number
    └─┴─┴─┴─┴─┴─┴─┴────────────  low order 8 bits of track number

 - see   INT 13,STATUS   INT 13,3

:int 13,c
^INT 13,C - Seek to Cylinder (XT & newer)

 AH = 0C
 CH = low order byte of cylinder number (see below)
 CL = high order byte of cylinder number (see below)
 DH = head number (0-15)
 DL = fixed drive number (80h=drive 0, 81h=drive 1)


 on return:
 AH = status  (see INT 13,STATUS)
 CF = 0 if successful
    = 1 if error


 - many good programming references indicate this function is only
   available on the AT, PS2 and later systems, but all hard disk
   systems since the XT have this function available
 - notice that CX is in reverse byte format similar to the way data
   is stored in memory and reverse of normal register storage
 - only the disk number is checked for validity
 - the parameters in CX change depending on the number of cylinders;
   the track/cylinder number is a 10 bit value taken from the 2 high
   order bits of CL and the 8 bits in CH (low order 8 bits of track):

   │F│E│D│C│B│A│9│8│7│6│5-0│  CX
    │ │ │ │ │ │ │ │ │ │  └─────  unused
    │ │ │ │ │ │ │ │ └─┴───────  high order 2 bits of track number
    └─┴─┴─┴─┴─┴─┴─┴──────────  low order 8 bits of track number

 - see   INT 13,STATUS

:int 13,d
^INT 13,D - Alternate Disk Reset  (XT & newer)

 AH = 0D
 DL = fixed drive number  (80h=drive 0, 81h=drive 1)


 on return:
 AH = status  (see INT 13,STATUS)
 CF = 0 if successful
    = 1 if error


 - many good programming references indicate this function is only
   available on the AT, PS2 and later systems, but all hard disk
   systems since the XT have this function available
 - used to force drive recalibration similar to INT 13,0
 - drive heads are positioned at track zero

 - see   INT 13,STATUS   INT 13,0

:int 13,e
^INT 13,E - Read Sector Buffer (XT & portable only)


 AH = 0E


 on return:
 AL = number of sectors actually transferred
 AH = status  (see INT 13,STATUS)
 CF = 0 if successful
    = 1 if error


 - see INT 13,STATUS for controller error codes

:int 13,f
^INT 13,F - Write Sector Buffer (XT & portable only)


 AH = 0F


 on return:
 AL = number of sectors actually transferred
 AH = status  (see INT 13,STATUS)
 CF = 0 if successful
    = 1 if error


 - see INT 13,STATUS for controller error codes

:int 13,10
^INT 13,10 - Test for Drive Ready (XT  & newer)


 AH = 10h
 DL = drive number (0=A:, 1=2nd floppy, 80h=drive 0, 81h=drive 1)


 on return:
 AH = status  (see INT 13,STATUS)
 CF = 0 if successful
    = 1 if error


 - many good programming references indicate this function is only
   available on the AT, PS2 and later systems, but all hard disk
   systems since the XT have this function available
 - see INT 13,STATUS for controller error codes

:int 13,11
^INT 13,11 - Recalibrate Drive (XT & newer)


 AH = 11h
 DL = drive number (0=A:, 1=2nd floppy, 80h=drive 0, 81h=drive 1)


 on return:
 AH = status  (see INT 13,STATUS)
 CF = 0 if successful
    = 1 if error


 - many good programming references indicate this function is only
   available on the AT, PS2 and later systems, but all hard disk
   systems since the XT have this function available

 - see INT 13,STATUS for controller error codes

:int 13,12
^INT 13,12 - Controller RAM Diagnostic (XT & portable only)


 AH = 12h


 on return:
 AH = status  (see INT 13,STATUS)
 CF = 0 if successful
    = 1 if error


 - see INT 13,STATUS for controller error codes

:int 13,13
^INT 13,13 - Drive Diagnostic (XT & portable only)


 AH = 13h


 on return:
 AH = status  (see INT 13,STATUS)
 CF = 0 if successful
    = 1 if error


 - see INT 13,STATUS for controller error codes

:int 13,14
^INT 13,14 - Controller Internal Diagnostic (XT & newer)


 AH = 14h


 on return:
 AH = status  (see INT 13,STATUS)
 CF = 0 if successful
    = 1 if error


 - many good programming references indicate this function is only
   available on the AT, PS2 and later systems, but all hard disk
   systems since the XT have this function available
 - not valid on PS2 model 30

 - see INT 13,STATUS for controller error codes

:int 13,15
^INT 13,15 - Read DASD Type (XT BIOS from 1/10/86 & newer)

 AH = 15h
 DL = drive number (0=A:, 1=2nd floppy, 80h=drive 0, 81h=drive 1)


 on return:
 AH = 00 drive not present
    = 01 diskette, no change detection present
    = 02 diskette, change detection present
    = 03 fixed disk present
 CX:DX = number of fixed disk sectors; if 3 is returned in AH
 CF = 0 if successful
    = 1 if error


 - XT's must have a BIOS date 1/10/86 or newer
 - used to determine if INT 13,16 can detect disk change

 - see   INT 13,STATUS   INT 13,16
:int 13,16
^INT 13,16 - Change of Disk Status (XT BIOS from 1/10/86 & newer)


 AH = 16h
 DL = drive number (0=A:, 1=2nd floppy, 80h=drive 0, 81h=drive 1)


 on return:
 AH = 00 no disk change
    = 01 disk changed
 CF = set if disk has been removed or an error occurred


 - used to detect if a disk change has occurred
 - see   INT 13,STATUS   INT 13,15

:int 13,17
^INT 13,17 - Set DASD Type for Format (XT BIOS from 1/10/86 & newer)


 AH = 17h
 AL = 00 no disk
    = 01  320k/360k diskette in 320k/360k drive
    = 02  320k/360k diskette in 1.2Mb drive
    = 03  1.2Mb diskette in 1.2Mb drive
    = 04  720k diskette in 720k drive  (BIOS 6/10/85 & newer)
          720K diskette in 1.44Mb drive (PS2)
          1.44Mb diskette in 1.44Mb drive (PS2)
 DL = drive number (0=A:, 1=2nd floppy, 80h=drive 0, 81h=drive 1)


 returns nothing


 - only the disk number is checked for validity
 - tells BIOS format routine about the disk type

:int 13,18
^INT 13,18 - Set Media Type for Format (BIOS date specific)


 AH = 18h
 CH = lower 8 bits of number of tracks  (0-1023 dec., see below)
 CL = sectors per track (1-17 dec., see below)
 DL = drive number (0=A:, 1=2nd floppy, 80h=drive 0, 81h=drive 1)


 on return:
 ES:DI = pointer to 11-byte Disk Base Table (DBT)
 AH = 00h if requested combination supported
    = 01h if function not available
    = 0Ch if not supported or drive type unknown
    = 80h if there is no media in the drive
 CF = 0 if successful
    = 1 if error


 - valid only for XT BIOS dated after 1/10/86, AT after 11/15/86,
   XT 286 and the PS2 line
 - only disk number is checked for validity
 - track number is a 10 bit value taken from the 2 high order
   bits of CL and the 8 bits in CH (low order 8 bits of track):

   │F│E│D│C│B│A│9│8│7│6│5│4│3│2│1│0│  CX
    │ │ │ │ │ │ │ │ │ │ └─┴─┴─┴─┴─┴────  sectors per track count
    │ │ │ │ │ │ │ │ └─┴────────────  high order 2 bits track/cyl count
    └─┴─┴─┴─┴─┴─┴─┴────────────  low order 8 bits of track/cyl count

 - see   DBT   DISK BASE TABLE   INT 13,STATUS

:int 13,19
^INT 13,19 - Park Fixed Disk Heads (AT & newer)


 AH = 19h
 DL = drive number (0=A:, 1=2nd floppy, 80h=drive 0, 81h=drive 1)


 on return:
 AH = status  (see INT 13,STATUS)
 CF = 0 if successful
    = 1 if error


 - available only on AT, XT 283 and PS2 machines

 - see INT 13,STATUS

:int 13,1a
^INT 13,1A - Format Unit (PS2 model 50+)

 AH = 1Ah
 AL = defect table count
 DL = drive number (0=A:, 1=2nd floppy, 80h=drive 0, 81h=drive 1)
 ES:BX = far pointer to defect table
 CL = modifier bits

    │7│6│5│4│3│2│1│0│  Format Unit Modifier Bits
     │ │ │ │ │ │ │ └──── 1=ignore primary defect map, 0=use map
     │ │ │ │ │ │ └───── 1=ignore secondary defect map, 0=use map
     │ │ │ │ │ └────── 1=update secondary defect map, 0=don't
     │ │ │ │ └─────── 1=do extended surface analysis, 0=don't
     │ │ │ └──────── 1=periodic interrupt status on, 0=off
     └─┴─┴───────── reserved

 returns nothing

 - only the disk number is checked for validity

 - see   INT 13,STATUS
:int 14:bios serial services:bios communications:int 14,status
^INT 14 - BIOS Asynchronous Communications Services

%Function requested in AH; see also  INT 14,N  where N is:

    0 - Initialize serial port parameters  (see INT 14,0)
    1 - Send character in AL  (see INT 14,1)
    2 - Receive character in AL  (see INT 14,2)
    3 - Get Serial port status  (see INT 14,3)
    4 - Extended initialize  (PS2) (see INT 14,4)
    5 - Extended communication port control (PS2) (see INT 14,5)


 - all functions have:
   AH = function number
   AL = character to send or receive
   DX = zero based RS232 card number
 - these functions use hardware flow control
 - used by DOS MODE to redirect LPTx output to a serial device
 - see individual functions for more data.


^BIOS Asynchronous Communications Services (Status)

 │7│6│5│4│3│2│1│0│  AL  modem status
  │ │ │ │ │ │ │ └──── clear to send status changed
  │ │ │ │ │ │ └───── data set ready status changed
  │ │ │ │ │ └────── trailing edge ring indicator
  │ │ │ │ └─────── receive line signal changed
  │ │ │ └──────── clear to send
  │ │ └───────── data set ready
  │ └────────── ring indicator
  └─────────── receive line signal detected

 │7│6│5│4│3│2│1│0│  AH  port status
  │ │ │ │ │ │ │ └──── data ready
  │ │ │ │ │ │ └───── overrun error
  │ │ │ │ │ └────── parity error
  │ │ │ │ └─────── framing error
  │ │ │ └──────── break detect
  │ │ └───────── transmit holding register empty
  │ └────────── transmit shift register empty
  └─────────── time out (N/A for functions 1 and 2)

:int 14,0
^INT 14,0 - Initialize Communications Port Parameters

 AH = 00
 AL = parms for initialization (see tables below)
 DX = zero based serial port number (0-1) (0-3 for AT)

 │7│6│5│4│3│2│1│0│  AL                      Parity (bits 4 & 3)
  │ │ │ │ │ │ └─┴──── word length bits          00 = none
  │ │ │ │ │ └─────── stop bits flag             01 = odd
  │ │ │ └─┴──────── parity bits                 10 = none
  └─┴─┴─────────── baud rate bits               11 = even

%Word length (bits 1 & 0)            Stop bit count (bit 2)

    10 = 7 bits                        0 = 1 stop bit
    11 = 8 bits                        1 = 2 stop bits

%Baud rate (bits 7, 6 & 5)

 000 = 110 baud      100 = 1200 baud
 001 = 150 baud      101 = 2400 baud
 010 = 300 baud      110 = 4800 baud
 011 = 600 baud      111 = 9600 baud (4800 on PCjr)


 on return:
 AH = port status
 AL = modem status


 - for status bits see INT 14,STATUS

:int 14,1
^INT 14,1 - Send Character to Communications Port


 AH = 01
 AL = character to send
 DX = zero based serial port number (0-1) (0-3 for AT)


 on return:
 AH = port status  (see INT 14,STATUS)
      bit 7=0 indicates success
      bit 7=1 indicates error, bits 0-6 indicate cause


 - INT 14 service 3 should be used to determine the actual
   cause of the error since the time-out bit of the status
   register is always set during an error on this call
 - uses hardware flow control
 - for status bits see INT 14,STATUS

:int 14,2
^INT 14,2 - Receive Character from Communications Port

 AH = 02
 DX = zero based serial port number (0-1) (0-3 for AT)


 on return:
 AH = port status  (see INT 14,STATUS)
      bit 7 = 0 if successful
      bit 7 = 1 if call failed
 AL = character received if call was success


 - INT 14 service 3 should be used to determine the actual
   cause of the error since the time-out bit of the status
   register is always set during an error on this call
 - uses hardware flow control

 - for status bits see INT 14,STATUS

:int 14,3
^INT 14,3 - Get Serial Port Status


 AH = 03
 DX = zero based serial port number (0-1) (0-3 for AT)


 on return:
 AH = port status
 AL = modem status


 - the status check performs a poll of the port and does not
   perform character I/O

 - for status bits see  INT 14,STATUS

:int 14,4
^INT 14,4 - Serial Port Extended Initialization (PS2 only)

 AH = 04
 AL = break setting
 BH = parity setting
 BL = stop bit setting
 CH = word length setting
 CL = baud rate setting
 DX = zero based serial port number (0-3)

%                 --- Break Setting ---
                       1 = break
                       0 = no break

%----- Parity Setting -----        --- Stop Bit Setting ---

    0 = no parity                   0 = one stop bit
    1 = odd parity                  1 = 2 stop bits
    2 = even parity                     1½ if register CH=0
    3 = stick parity odd                (5 bit word length)
    4 = stick parity even

%-- Word Length Setting --       ---- Baud rate Setting ----

        0 = 5 bits                 0 = 110       5 = 2400
        1 = 6 bits                 1 = 150       6 = 4800
        2 = 7 bits                 2 = 300       7 = 9600
        3 = 8 bits                 3 = 600       8 = 19200
                                   4 = 1200

 on return:
 AH = port status
 AL = modem status


 - for status bits see INT 14,STATUS

:int 14,5
^INT 14,5 - Extended Communication Port Control  (PS2 only)

 AH = 05
 AL = read or write modem control register
    = 00 read modem control register
    = 01 read modem control register
 DX = zero based serial port number (0-1) (0-3 for AT)

 BL = modem control register

      │7│6│5│4│3│2│1│0│  BL
       │ │ │ │ │ │ │ └──── 1 = activate data terminal ready
       │ │ │ │ │ │ └───── 1 = activate request to send
       │ │ │ │ │ └────── OUT1
       │ │ │ │ └─────── OUT2
       │ │ │ └──────── 0 = normal, 1 = loopback test
       └─┴─┴───────── reserved, forced to zero

 on return:
 AH = port status,  see INT 14,STATUS
 AL = modem status,  see INT 14,STATUS
 BL = UART modem control register, see UART

:int 15:bios system services:system interrupts
^INT 15 - System BIOS Services

%Function requested in AH; see also  INT 15,N  where N is:

     0 - Turn cassette motor on (PC,PCjr only)
     1 - Turn cassette motor off (PC,PCjr only)
     2 - Read blocks from cassette (PC,PCjr only)
     3 - Write blocks to cassette (PC,PCjr only)
     F - PS2 format periodic interrupt (PS2 only)
    21 - PS2 power on self test (PS2 except 30)
    40 - Read / modify profiles (convertible only)
    41 - Wait on external event (convertible only)
    42 - Request system power off (convertible only)
    43 - Read system status (convertible only)
    44 - (De)activate internal modem power (convertible)
    4F - Keyboard intercept  (BIOS date specific)
    80 - Device open
    81 - Device close
    82 - Program termination
    83 - Event wait
    84 - Joy-Stick support
    85 - System request key pressed
    86 - Elapsed time wait (AT and after)
    87 - Move block to/from extended memory
    88 - Extended memory size determination
    89 - Switch processor to protected mode
    90 - Device busy
    91 - Interrupt complete
    C0 - Return system configuration parameters (PS2 only)
    C1 - Return extended BIOS data address (PS2 only)
    C2 - Pointing device BIOS interface (PS2 only)
    C3 - Enable/Disable watchdog timer
    C4 - Programmable option select


 - CF is set and AX is left unchanged if function isn't supported
 - some Tandy BIOS's fail to restore interrupts on return from INT 15

:int 15,0
^INT 15,0 - Turn Cassette Motor On (PC,PCjr only)


 AH = 00


 - all programs using the cassette must actually turn on
   the device before use
 - there is a noticeable delay between turn-on and device ready
 - a noticeable clicking noise can be heard by switching the
   cassette on and off

 - see INT 15,1

:int 15,1
^INT 15,1 - Turn Cassette Motor Off (PC,PCjr only)


 AH = 01


 - all programs using the cassette should turn off
   the device after use
 - a noticeable clicking noise can be heard by switching the
   cassette on and off

 - see  INT 15,0

:int 15,2
^INT 15,2 - Read Blocks from Cassette (PC,PCjr only)

 AH = 02
 CX = count of bytes to read
 ES:BX = pointer to data buffer


 on return:

 AH = error code if CF=1
    = 1  if CRC error
    = 2  data transition lost, (bit signal scrambled)
    = 3  no data found on tape

 DX = count of bytes actually read
 ES:BX = pointer to byte following last byte read


 - data is transferred in 256 byte blocks, though only the
   number of bytes requested are actually stored

:int 15,3
^INT 15,3 - Write Blocks to Cassette (PC,PCjr only)


 AH = 03
 CX = count of bytes to write
 ES:BX = pointer to data buffer


 on return:

 CX = zero
 ES:BX = pointer to byte following last byte written


 - data is actually written in 256 byte blocks
 - if CX is less than 256, then the block is padded
 - no error detection/correction is available for writing

:int 15,f
^INT 15,F - Format Periodic Interrupt (PS2 only)

 AH = 0F
 AL = phase code
    = 00  reserved
    = 01  surface analysis
    = 02  formatting

 on return:
 CF = 0 continue formatting/scanning
    = 1 end of format/scanning

 - after formatting/scanning each cylinder the formatting
   routine calls this interrupt
 - may be used by a program to gain control after formatting
   a cylinder
 - if invoked from a non-PS2 CF=1 and AH contains the following
   AH = 80h  for PC and PCjr
      = 86h  on most other machines


:int 15,21
^INT 15,21 - Power On Self Test (POST) Error Log  (PS2 except 30)

 AH = 21h
 AL = 00 read POST error log
    = 01 write error code to POST error log
 BH = Device code  (if write)
 BL = Device error  (if write)

 on return
 CF = 0 if successful
    = 1 if in error (AH contains code)

%if reading POST error log:
    AH = 00h if successful
       = 80h (PCjr and PC)        = 86h for all other machines
    BX = number of POST error codes stored
    ES:DI pointer to POST error log

%if writing POST error log:
    AH = 00h if successful        = 01 POST error log full
       = 80h (PCjr and PC)        = 86h for all other machines
:int 15,40
^INT 15,40 - Read / Modify Profiles (convertible only)


 AH = 40h

 AL = 00 - return system profile in cx,bx
      01 - modify system profile
      CX,BX = profile info


 AL = 02 - return internal modem profile in BX


 AL = 03 - modify internal modem profile
      BX = profile info

:int 15,41
^INT 15,41 - Wait on External Event (convertible only)

 AH = 41h
 AL = condition type:

  │7│6│5│4│3│2│1│0│  AL
   │ │ │ │ │ └─┴─┴──── conditions (codes) to wait for
   │ │ │ │ └───────── reserved
   │ │ │ └────────── 1=port address/0=user byte
   └─┴─┴─────────── reserved

%Condition codes:

      0 = any external event
      1 = compare and return if equal
      2 = compare and return if not equal
      3 = test and return if not zero
      4 = test and return if zero

 BH = condition compare or mask value
 BL = time-out value times 55 ms, 0 if no time limit
 DX = I/O port address (if AL bit 4 = 1)
 ES:DI = pointer to user byte (if AL bit 4 = 0)

:int 15,42
^INT 15,42 - Request System Power Off (convertible only)


 AH = 42h

 AL = 00 to use system profile
    = 01 to force suspend regardless of profile

:int 15,43
^INT 15,43 - Read System Status (convertible only)


 AH = 43h


 on return
 AL = STATUS:

   │7│6│5│4│3│2│1│0│  AL
    │ │ │ │ │ │ │ └──── LCD detached
    │ │ │ │ │ │ └───── reserved
    │ │ │ │ │ └────── RS232/parallel powered on
    │ │ │ │ └─────── internal modem powered on
    │ │ │ └──────── power activated by alarm
    │ │ └───────── standby power lost
    │ └────────── external power in use
    └─────────── battery low

:int 15,44
^INT 15,44 - (De)activate Internal Modem Power (convertible)


 AH = 44h

 AL = 00 to power off
    = 01 to power on

:int 15,4f
^INT 15,4F - Keyboard Intercept  (BIOS date specific)

 AH = 4F
 AL = scan code
 CF = set to 1 (via STC instruction)

 on return

 AH = 80h, CF set  (PC, PCjr)
    = 86h, CF set  (XT BIOS 11/8/82, AT BIOS 1/10/84)
 AL = CF set, new scan code
    = CF clear, original scancode


 - available with XT BIOS after 11/8/82, AT BIOS after 1/10/84
 - called by INT 9, makes allowance for keyboard translation
 - normally returns the scan code in AL, with CF set
 - if function returns with CF clear, INT 9 ignores keystroke
 - do not rely on this function being called for each INT 9 since
   any user INT 9 handler can exit prematurely and circumvent
   this function
:int 15,80
^INT 15,80 - Device Open


 AH = 80h
 BX = device id
 CX = process id


 on return:
 CF = 0 if successful
    = 1 if error
 AH = 80h for PC & PCjr
    = 86h for XT (BIOS after 11/8/82)


 - available on the AT, XT 286, PS2 and XT with BIOS after 11/8/82
 - designed for use in simple multitasking

:int 15,81
^INT 15,81 - Device Close


 AH = 81h
 BX = device id
 CX = process id


 on return:
 CF = 0 if successful
    = 1 if error
 AH = 80h for PC & PCjr
    = 86h for XT (BIOS after 11/8/82)


 - available on the AT, XT 286, PS2 and XT with BIOS after 11/8/82
 - designed for use in simple multitasking

:int 15,82
^INT 15,82 - Program Termination


 AH = 82h
 BX = device id


 on return:
 CF = 0 if successful
    = 1 if error
 AH = 80h for PC & PCjr
    = 86h for XT (BIOS after 11/8/82)


 - available on the AT, XT 286, PS2 and XT with BIOS after 11/8/82
 - designed for use in simple multitasking

:int 15,83
^INT 15,83 - Event Wait


 AH = 83h
 AL = 0  set interval
    = 1  cancel interval (PS2)
 CX,DX = number of microseconds to wait (976 µs resolution)
 ES:BX = pointer to memory flag (bit 7 is set
         when interval expires)
       (granularity is 976 microseconds)


 on return:
 CF = 1 if function already busy
 AH = 80h for PC
    = 86h for XT & AT


 - available on the AT (BIOS after 1/10/84) and PS2's except 30
 - designed for use in simple multitasking

:int 15,84
^INT 15,84 - Joy-Stick Support


 AH = 84h
 DX = 0 to read the current switch settings
    = 1 to read the joystick position (resistive inputs)


 on return (DX=0, read switch setting):
 CF = 0 if successful
    = 1 if error
 AH = 80h error code if CF set on PC
    = 86h error code if CF set on XT before 11/8/82
 AL = switch settings in bits 7-4 (if read switch function)

 on return (DX=1, read joystick position):
 AX = A(X)
 BX = A(Y)
 CX = B(X)
 DX = B(Y)

:int 15,85
^INT 15,85 - System Request Key Pressed


 AH = 85h
 AL = 00 key pressed
    = 01 key released


 on return:
 CF = 0 if successful
    = 1 if error
 AH = 80h for PC or PCjr
    = 86h for XT (BIOS after 11/8/82)


 - called by BIOS when the System Request key is pressed/released
 - available on machines with newer BIOS and keyboards

:int 15,86
^INT 15,86 - Elapsed Time Wait (AT and PS2)


 AH = 86h
 CX,DX = number of microseconds to wait (976 µs resolution)


 on return:
 CF = set if error (PC,PCjr,XT)
    = set if wait in progress
    = clear if successful wait
 AH = 80h for PC and PCjr
    = 86h for XT


 - AT and PS2 only for system timing
 - not designed for user application usage

:int 15,87
^INT 15,87 - Move Block to/from Extended Memory

 AH = 87h
 CX = word count of block to be moved
 ES:SI = pointer to Global Descriptor Table (GDT)


 on return:
 CF = 0  if successful (AH contains return code)
    = 1  if error detected
 AH = 0  operation successful (ZF also set)
    = 1  RAM parity error  (if CF set)
    = 2  other exception (if CF set)
    = 3  gate address on line 20h failed (if CF set)
    = 80h on PC and PCjr (if CF set)
    = 86h on XT and newer 808x machines (if CF set)

 - transfers data blocks to and from extended memory on 80286
   and 80386 machines by switching from real to protected mode
   for the duration of the transfer
 - all real mode interrupts are disabled
 - processor shuts down during the switch from protected mode
   to real mode on 286 processors

 - see   GDT

:int 15,88
^INT 15,88 - Extended Memory Size Determination


 AH = 88h


 on return:
 CF = 80h for PC, PCjr
    = 86h for XT and Model 30
    = other machines, set for error, clear for success
 AX = number of contiguous 1k blocks of memory starting
      at address 1024k (100000h)


 - works only on 80286 and 80386 machines
 - retrieves bytes 30 and 31 from the CMOS RAM (this data is set
   by the boot memory scan

:int 15,89
^INT 15,89 - Switch Processor to Protected Mode

 AH = 89h
 BH = IRQ8 interrupt vector offset
 BL = IRQ0 interrupt vector offset
 CX = offset into protected mode CS to jump
 ES:SI = pointer to Global Descriptor Table (GDT)


 on return:
 CF = 0 if successful
    = 1 if error

 - switches 286 and 386 machines into protected mode to take
   advantage of advanced feature and extended memory
 - Global descriptor table must be setup before interrupt
 - normal BIOS functions are not available after the switch


 - see   GDT
:int 15,90
^INT 15,90 - Device Busy

 AH = 90h
 AL = type code:
    = 00  disk
    = 01  diskette
    = 02  keyboard
    = 03  pointing device
    = 80  network (ES:BX = NCB)
    = FC  fixed disk reset (PS2)
    = FD  diskette motor start
    = FE  printer
 ES:BX = pointer to network control block if waiting for network

 on return:
 CF = 0 if wait not satisfied
    = 1 if wait time satisfied
 AH = when CF set, 80h for PC & PCjr, 86h for XT (BIOS 11/8/82)

 - tells the OS a a program is about to wait for a device
 - used for multitasking OS development
:int 15,91
^INT 15,91 - Interrupt Complete

 AH = 91h

 on return:
 CF = 0 if successful
    = 1 if error
 AH = when CF set, 80h for PC & PCjr, 86h for XT (BIOS 11/8/82)
 AL = type code:
    = 00  disk
    = 01  diskette
    = 02  keyboard
    = 03  pointing device
    = 80  network (ES:BX = NCB)
    = FC  fixed disk reset (PS2)
    = FD  diskette motor start
    = FE  printer

 - should not be used by applications software
 - used by the BIOS to indicate device interrupt is complete
 - used for multitasking OS development
:int 15,c0
^INT 15,C0 - Return System Configuration Parameters (PS2 only)

 AH = C0

 on return:
 CF = 0 if successful
    = 1 if error
 AH = when CF set, 80h for PC & PCjr, 86h for XT
      (BIOS after 11/8/82) and AT (BIOS after 1/10/84)

 ES:BX = pointer to system descriptor table in ROM of the format:

%Offset Size          Description

   00   word   length of descriptor (8 minimum)
   02   byte   model byte (same as F000:FFFE, not reliable)
   03   byte   secondary model byte
   04   byte   BIOS revision level (zero based)
   05   byte   feature information, see below
   06   dword  reserved


%Feature Information

 │7│6│5│4│3│2│1│0│  Feature Byte
  │ │ │ │ │ │ │ └──── reserved
  │ │ │ │ │ │ └───── 0=PC bus, 1=Micro Channel
  │ │ │ │ │ └────── Extended BIOS Data Area allocated
  │ │ │ │ └─────── wait for external event supported
  │ │ │ └──────── INT 15 AH=4F used (kbd intercept)
  │ │ └───────── RTC present
  │ └────────── 2nd 8259 present
  └─────────── DMA channel 3 used by fixed disk BIOS

 - see   MACHINE ID

:int 15,c1
^INT 15,C1 - Return Extended BIOS Data Area Segment (PS2 only)


 AH = C1


 on return:
 CF = 0 if successful
    = 1 if error
 AH = when CF set, 80h for PC & PCjr, 86h for XT (BIOS 11/8/82)
 ES = EBDA segment address if PS2


 - the EBDA is used internally by the PS2 BIOS routines
 - the EBDA is allocated at the top of user memory by the POST
   routine

:int 15,c2
^INT 15,C2 - Pointing Device BIOS Interface  (PS2 only)

 AH = C2
 AL = 0  enable/disable pointing device (BH contains flag)
    = 1  reset pointing device
    = 2  set sample rate
    = 3  set resolution
    = 4  read device type
    = 5  pointing device initialization
    = 6  extended commands
    = 7  pointing device far call initialization
 BH = 0 indicates enable for AL = 0
    = 1 indicates disable for AL = 0


 on return:
 CF = 0 if successful
    = 1 if error
 AH = when CF set, 80h for PC & PCjr, 86h for XT, AT
    = 01  invalid function call
    = 02  invalid input
    = 03  interface error
    = 04  resend
    = 05  no far call installed

:int 15,c3
^INT 15,C3 - Enable/Disable Watchdog Timer  (PS2)

 AH = C3
 AL = 0  disable watchdog time-out
    = 1  enable watchdog time-out
 BX = watchdog timer count (1-255)


 on return:
 CF = 0 if successful
    = 1 if error
 AH = when CF set, 80h for PC & PCjr, 86h for XT, AT & Model 30


 - the watchdog timer is available only on PS2 with 80286 and
   80386 processors.
 - the timer uses channel timer channel 3 and IRQ0.  Activated
   when IRQ0 is active for more than one channel 0 timer cycle,
   which causes the timer to be decremented.   When the watch-
   dog timer reaches 0, and NMI is generated.
:int 15,c4
^INT 15,C4 - Programmable Option Select  (PS2)

 AH = C4
 AL = 0  get Programmable Option Select adapter register address
    = 1  enable slot for setup
    = 2  adapter enable


 on return:
 CF = 0 if successful
    = 1 if error
 AH = when CF set, 80h for PC & PCjr, 86h for XT, AT & 30
 BL = slot number (function AL=1)
 DL = POS adapter register address (function AL=0)


 - allows access to PS2 Programmable Option Select registers
 - available on 80286 and 80386 PS2's

:int 16:bios keyboard services
^INT 16 - Keyboard BIOS Services


%Function requested in AH, see  INT 16,n  where n is:

    0 - Wait for keystroke and read
    1 - Get keystroke status
    2 - Get shift status
    3 - Set keyboard typematic rate (AT+)
    4 - Keyboard click adjustment (AT+)
    5 - Keyboard buffer write  (AT/PS2 enhanced keyboards)
   10 - Wait for keystroke and read  (AT/PS2 enhanced keyboards)
   11 - Get keystroke status  (AT/PS2 enhanced keyboards)
   12 - Get shift status  (AT/PS2 enhanced keyboards)


 - with IBM BIOS's, INT 16 functions do not restore the flags to
   the pre-interrupt state to allow returning of information via
   the flags register
 - functions 3 through 12h are not available on all AT machines
   unless the extended keyboard BIOS is present
 - see   SCAN CODES
:int 16,0
^INT 16,0 - Wait for Keypress and Read Character


 AH = 00


 on return:
 AH = keyboard scan code
 AL = ASCII character or zero if special function key


 - halts program until key with a scancode is pressed
 - see  SCAN CODES

:int 16,1
^INT 16,1 - Get Keyboard Status


 AH = 01


 on return:
 ZF = 0 if a key pressed (even Ctrl-Break)
 AX = 0 if no scan code is available
 AH = scan code
 AL = ASCII character or zero if special function key


 - data code is not removed from buffer
 - Ctrl-Break places a zero word in the keyboard buffer but does
   register a keypress.

:int 16,2
^INT 16,2 - Read Keyboard Flags

 AH = 02


 on return:
 AL = BIOS keyboard flags (located in BIOS Data Area 40:17)

   │7│6│5│4│3│2│1│0│  AL or BIOS Data Area 40:17
    │ │ │ │ │ │ │ └──── 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

 - see   BDA   BIOS DATA AREA

:int 16,3
^INT 16,3 - Set Keyboard Typematic Rate  (AT+)

 AH = 03
 AL = 00  set typematic rate to default
      01  increase initial delay
      02  slow typematic rate by 1/2
      04  turn off typematic chars
      05  set typematic rate/delay

 BH = repeat delay (AL=5)
      0 = 250ms     2 = 750ms
      1 = 500ms     3 = 1000ms
 BL = typematic rate, one of the following  (AL=5)

      00 - 30.0      01 - 26.7      02 - 24.0      03 - 21.8
      04 - 20.0      05 - 18.5      06 - 17.1      07 - 16.0
      08 - 15.0      09 - 13.3      0A - 12.0      0B - 10.9
      0C - 10.0      0D - 9.2       0E - 8.6       0F - 8.0
      10 - 7.5       11 - 6.7       12 - 6.0       13 - 5.5
      14 - 5.0       15 - 4.6       16 - 4.3       17 - 4.0
      18 - 3.7       19 - 3.3       1A - 3.0       1B - 2.7
      1C - 2.5       1D - 2.3       1E - 2.1       1F - 2.0

 returns nothing

 - if the typematic rate is not within range,no action is taken
 - available on AT and PS2 machines with extended keyboard support
 - see   KEYBOARD COMMANDS
:int 16,4
^INT 16,4 - Keyboard Click Adjustment (AT+)


 AH = 04
 AL = 1 for click on
    = 0 for click off


 - available only on AT and later machines that support the extended
   keyboard BIOS
:int 16,5
^INT 16,5 - Keyboard Buffer Write  (AT+)


 AH = 05
 CH = scan code
 CL = ASCII character


 on return:
 AL = 00 if success
      01 if buffer full


 - available on AT and PS2 machines with extended keyboard support
 - stores normal keystroke into keyboard buffer
 - will not store attribute keys like Shift, Alt, Ctrl, etc...

:int 16,10
^INT 16,10 - Extended Wait for Keypress and Read Character  (AT+)


 AH = 10h


 on return:
 AH = scan code
 AL = ASCII character or zero if special function key


 - available on AT and PS2 machines with extended keyboard support
 - similar to INT 16,0
 - see  SCAN CODES

:int 16,11
^INT 16,11 - Extended Get Keyboard Status  (AT+)


 AH = 11h


 on return:
 ZF = 0 if key pressed (data waiting)
 AX = 0 if no scan code is available
 AH = scan code
 AL = ASCII character or zero if special function key


 - available on AT and PS2 machines with extended keyboard support
 - data is not removed from buffer
 - similar to INT 16,1

:int 16,12
^INT 16,12 - Extended Get Keyboard Status  (AT+)

 AH = 12h

 on return:
 AH = BIOS keyboard flags (BIOS Data Area location 40:18)

   │7│6│5│4│3│2│1│0│  AH
    │ │ │ │ │ │ │ └──── left CTRL key depressed
    │ │ │ │ │ │ └───── left ALT key depressed
    │ │ │ │ │ └────── right CTRL key pressed
    │ │ │ │ └─────── right ALT key depressed
    │ │ │ └──────── scroll-lock depressed
    │ │ └───────── num-lock key depressed
    │ └────────── caps-lock key depressed
    └─────────── system request key depressed

 AL = BIOS keyboard flags (BIOS Data Area location 40:17)

   │7│6│5│4│3│2│1│0│  AL
    │ │ │ │ │ │ │ └──── 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


 - available on AT and PS2 machines with extended keyboard support
 - similar to INT 16,2

 - see   KB FLAGS

:int 17:bios printer services:int 17,status:printer status
^INT 17 - Printer BIOS Services

%Function requested in AH, see  INT 17,n  where n is:

    0 - Print character
    1 - Initialize printer port
    2 - Read printer port status

 Status flags returned in register AH

 │7│6│5│4│3│2│1│0│  AH (status)
  │ │ │ │ │ │ │ └────  time-out
  │ │ │ │ │ └─┴─────  unused
  │ │ │ │ └────────  1 = I/O error  (parallel pin 15)
  │ │ │ └─────────  1 = printer selected/on-line  (parallel pin 13)
  │ │ └──────────  1 = out of paper  (parallel pin 12)
  │ └───────────  1 = printer acknowledgment  (parallel pin 10)
  └────────────  1 = printer not busy  (parallel pin 11)

 - on the AT, XT 286, and PS2 when the BIOS determines the printer
   is busy,  INT 15,90  is executed
 - all printers do not return reliable status information;  bit 3 and
   bit 7 are usually reliable.
:int 17,0
^INT 17,0 - Print Character


 AH = 00
 AL = character to print
 DX = printer to be used (0-2)


 on return:
 AH = printer status


 - writes character and returns status
 - see  INT 17,STATUS  for printer status codes

:int 17,1
^INT 17,1 - Initialize Printer Port


 AH = 01
 DX = printer port to initialize (0-2)


 on return:
 AH = status


 - initializes printer port and returns status
 - outputs characters 0x08 and 0x0C to printer port which
   reset Epson and IBM printers, but may produce undesirable
   effects on other printers
 - see  INT 17,STATUS  for printer status codes

:int 17,2
^INT 17,2 - Read Printer Port Status

 AH = 02
 DX = printer port to be used (0-2)


 on return:
 AH = status

 │7│6│5│4│3│2│1│0│  Printer status bits
  │ │ │ │ │ │ │ └──── time out
  │ │ │ │ │ └─┴───── unused
  │ │ │ │ └──────── I/O error
  │ │ │ └───────── selected
  │ │ └────────── out of paper
  │ └─────────── acknowledge
  └──────────── not busy


 - returns status of specified printer port
:int 19
^INT 19 - Bootstrap Loader


 DL = physical drive where boot sector is located


 no output


 - track 0, sector 1 is loaded into address 0:7C00
   and control is transferred there
 - not a preferred method for rebooting by applications.  A
   better method is to set the word at location 40:72 to 1234h
   and jump to location FFFF:0 in ROM
 - memory is not cleared when rebooted through this interrupt

 - see   WARM BOOT

:int 1a:bios clock services
^INT 1A - System and Real Time Clock BIOS Services


%Function requested in AH; see also  INT 1A,N  where N is:

   0 - Read system clock counter
   1 - Set system clock counter
   2 - Read real time clock time (AT,PS2)
   3 - Set real time clock time (AT,PS2)
   4 - Read real time clock date (AT,PS2)
   5 - Set real time clock date (AT,PS2)
   6 - Set real time clock alarm (AT,PS2)
   7 - Reset real time clock alarm (PS2)
   8 - Set RTC activated power on mode (convertible,PS2)
   9 - Read RTC alarm time and status (convertible,PS2)
   A - Read system day counter (PS2)
   B - Set system day counter (PS2)
  80 - Set up sound multiplexer (PCjr only)

 - see   RTC
:int 1a,0
^INT 1A,0 - Read System Clock Counter


 AH = 00


 on return:
 AL = midnight flag, 1 if 24 hours passed since reset
 CX = high order word of tick count
 DX = low order word of tick count


 - incremented approximately 18.206 times per second
 - at midnight CX:DX is zero

:int 1a,1
^INT 1A,1 - Set System Clock Counter


 AH = 01
 CX = high order word of tick count
 DX = low order word of tick count


 returns nothing


 - CX:DX should be set to the number of seconds past
   midnight multiplied by approximately 18.206

:int 1a,2
^INT 1A,2 - Read Time From Real Time Clock  (XT 286,AT,PS2)


 AH = 02


 on return:
 CF = 0 if successful
    = 1 if error, RTC not operating
 CH = hours in BCD
 CL = minutes in BCD
 DH = seconds in BCD
 DL = 1 if daylight savings time option


 - on AT with BIOS before 6/10/85, DL is not returned
 - see   RTC
:int 1a,3
^INT 1A,3 - Set Time on Real Time Clock  (XT 286,AT,PS2)


 AH = 03
 CH = hours in BCD
 CL = minutes in BCD
 DH = seconds in BCD
 DL = 1 if daylight savings time option
    = 0 if standard time


 returns nothing


 - clock values must be in BCD
 - see   RTC
:int 1a,4
^INT 1A,4 - Read Real Time Clock Date  (XT 286,AT,PS2)


 AH = 04


 on return:
 CH = century in BCD (decimal 19 or 20)
 CL = year in BCD
 DH = month in BCD
 DL = day in BCD
 CF = 0 if successful
    = 1 if error or clock not operating

 - see   RTC
:int 1a,5
^INT 1A,5 - Set Real Time Clock Date  (XT 286,AT,PS2)


 AH = 05
 CH = century in BCD (decimal 19 or 20)
 CL = year in BCD
 DH = month in BCD
 DL = day in BCD


 returns nothing


 - all values must be in BCD
 - see   RTC
:int 1a,6
^INT 1A,6 - Set Real Time Clock Alarm  (XT 286,AT,PS2)


 AH = 06
 CH = hours in BCD
 CL = minutes in BCD
 DH = seconds in BCD


 on return:
 CF = 1 if alarm already set or clock inoperable


 - alarm setting is not relative like some sources claim, but the
   actually clock time the interrupt should occur
 - settings values must be in BCD
 - when the alarm time is reached INT 4A is executed
 - INT 4A vector should be replaced with address of the alarm
   handling interrupt routine before setting the alarm
 - INT 1A,7 should be called to disable the RTC alarm
 - see   RTC
:int 1a,7
^INT 1A,7 - Disable Real Time Clock Alarm  (XT,AT,PS2)


 AH = 07


 returns nothing


 - should be called previous to setting or resetting the
   RTC alarm with INT 1A,6
 - see   RTC
:int 1a,8
^INT 1A,8 - Set RTC Activated Power On Mode (convertible)


 AH = 08
 CH = hours in BCD
 CL = minutes in BCD
 DH = seconds in BCD


 - see   RTC
:int 1a,9
^INT 1A,9 - Read RTC Alarm Time and Status (convertible,PS2)


 AH = 09


 on return:
 CH = hours in BCD
 CL = minutes in BCD
 DH = seconds in BCD
 DL = alarm status:
    = 00 if alarm not enabled (AIE=0)
    = 01 if alarm enabled but will not power up system (AIE=1)
    = 02 if alarm will power up system (AIE=1)


 - see   RTC
:int 1a,a
^INT 1A,A - Read System Day Counter (PS2)


 AH = 0Ah


 on return:
 CX = count of days since 1-1-1980

:int 1a,b
^INT 1A,B - Set System Day Counter (PS2)


 AH = 0Bh
 CX = count of days since 1-1-1980

:int 1a,80
^INT 1A,80 - Setup Sound Multiplexer  (PCjr only)


 AL = 00 - source is 8253 channel 2
    = 01 - source is cassette input
    = 02 - source is I/O channel "AUDIO IN"
    = 03 - source is sound generator chip

:int 1b:bios break interrupt
^INT 1B - BIOS Ctrl-Break Handler Address


 - holds address of the BIOS Ctrl-Break interrupt handler
 - called by INT 9 after Ctrl-Break key is pressed; INT 9 sets the
   BIOS keyboard head and tail pointers to the buffer start and
   places a zero word in the buffer
 - the BIOS initially sets this value to point to a simple IRET but
   DOS re-vectors this to its own code, usually 2 lines of code that
   sets an internal flag (to 3) and then returns via IRET.
 - DOS checks this flag on entry to many of its subfunctions.  If the
   flag is set, it invokes INT 23h.
 - pointing this address to a null function with and IRET disables
   Ctrl-Break aborts
 - if the INT 1B code chooses to retain control of the system, it
   must issue an EOI for any interrupt pending on the 8259 and reset
   all I/O devices
 - should be terminated via an IRET
 - should not be called directly by user application

 - see    INT 9   INT 23

:int 1c:user timer routine
^INT 1C - System Timer Tick (User Routine)


 - called by interrupt 8, approximately 18.206 times per
   second (unless the program modifies the 8253 PIT
 - this is a user routine which the BIOS defaults to a simple IRET
 - this interrupt vector can be used for TSR popup utilities,
   animated graphics updates and event polling
 - since many TSR's don't maintain the integrity of the interrupt
   call chain, relying on this for TSR popup isn't recommended

 - see   INT 8   8253

:int 1d
^INT 1D - Video Initialization Parameter Table Vector


 - not a true interrupt, but a far pointer to a video
   initialization parameter table for video controllers

:int 1e
^INT 1E - Disk Initialization Parameter Table Vector

 - not an interrupt, but a far pointer to the diskette base table
 - this table contains initialization parameters for the disk
   controller used during formatting, reading, and writing to a disk

%Disk Initialization Parameter Table Vector Definition:

%Offset     Description

   00  │7│6│5│4│3│2│1│0│  Disk Controller Mode byte 1
        │ │ │ │ └─┴─┴─┴────  head step rate in milliseconds (0-F)
        └─┴─┴─┴───────────  head unload time in milliseconds (0-F)

   01  │7│6│5│4│3│2│1│0│  Disk Controller Mode byte 2
        │ │ │ │ │ │ │ └──── DMA flag (0 = use DMA)
        └─┴─┴─┴─┴─┴─┴───── (head load time/2)-1 in milliseconds

   02  clock ticks until motor off
   03  FM or MFM Mode:  Log2 (Bytes per Sector/128)
       FM=Frequency Modulation used on single-density disks
       MFM=Modified Frequency Modulation used on double-sided disks
   04  last sector on track
   05  gap length in bytes:

              Bytes Per   Sectors     Write    Format
       MFM     Sector    Per Track     Gap       Gap
        1        256         18        0Ah       0Ch
        1        256         16        20h       32h
        2        512          8        2Ah       50h
        2        512          9        1Bh       6Ch
        3       1024          4        80h       F0h
        4       2048          2        C8h       FFh
        5       4096          1        C8h       FFh

   06  disk data length
       80h for 128 bytes/sector
       FFh otherwise
   07  gap length when formatting
   08  data pattern used during formatting
   09  floppy head bounce delay (in milliseconds)
   0A  floppy motor start delay (in 0.125 second intervals)
   0B  floppy motor stop delay (in 0.25 second intervals)

 - see INT 13,18

:int 1f
^INT 1F - Graphics Display Character Bit Map Table


 - not a true interrupt, but a far pointer to a table of
   character bit maps for the graphics mode representation of
   ASCII characters 128 through 255
 - can be used to change character fonts in CGA graphics mode

:dos interrupts
^DOS Interrupt Summary


 See the following for more information:

    INT 20 - Program terminate
    INT 21 - DOS Function Dispatcher
    INT 22 - Program Terminate
    INT 23 - Ctl-break exit address
    INT 24 - Critical error handler address
    INT 25 - Absolute disk read
    INT 26 - Absolute disk write
    INT 27 - Terminate but stay resident
    INT 28 - DOS idle loop/scheduler (undocumented)
    INT 29 - Fast character output (undocumented)
    INT 2E - Execute command using base level COMMAND.COM (undoc.)
    INT 2F - Multiplex interrupt (DOS 3.x+)

:int 20
^INT 20 - Program Terminate


 CS = address of PSP


 returns nothing


 - INT 20 restores the terminate, ctl-break, and critical error
   exit addresses from values in the PSP, flushes all buffers, frees
   memory and returns to DOS via the termination handler address
 - does not close FCBs
 - this function is no longer recommended, but can be used by
   version of DOS before 2.0
 - see   INT 21,4C   INT 21,0

:int 21:dos services:dos functions
^INT 21 - DOS Function Dispatcher

%Function requested in AH; see also  INT 21,N  where N is:

    0 - Program terminate
    1 - Keyboard input with echo
    2 - Display output
    3 - Wait for auxiliary device input
    4 - Auxiliary output
    5 - Printer output
    6 - Direct console I/O
    7 - Wait for direct console input without echo
    8 - Wait for console input without echo
    9 - Print string
    A - Buffered keyboard input
    B - Check standard input status
    C - Clear keyboard buffer, invoke keyboard function
    D - Disk reset
    E - Select disk
    F - Open file using FCB
   10 - Close file using FCB
   11 - Search for first entry using FCB
   12 - Search for next entry using FCB
   13 - Delete file using FCB
   14 - Sequential read using FCB
   15 - Sequential write using FCB
   16 - Create a file using FCB
   17 - Rename file using FCB
   18 - DOS dummy function (CP/M) (not used/listed)
   19 - Get current default drive
   1A - Set disk transfer address
   1B - Get allocation table information
   1C - Get allocation table info for specific device
   1D - DOS dummy function (CP/M) (not used/listed)
   1E - DOS dummy function (CP/M) (not used/listed)
   1F - Get pointer to default drive parameter table (undocumented)
   20 - DOS dummy function (CP/M) (not used/listed)
   21 - Random read using FCB
   22 - Random write using FCB
   23 - Get file size using FCB
   24 - Set relative record field for FCB
   25 - Set interrupt vector
   26 - Create new program segment
   27 - Random block read using FCB
   28 - Random block write using FCB
   29 - Parse filename for FCB
   2A - Get date
   2B - Set date
   2C - Get time
   2D - Set time
   2E - Set/reset verify switch
   2F - Get disk transfer address
   30 - Get DOS version number
   31 - Terminate process and remain resident
   32 - Get pointer to drive parameter table (undocumented)
   33 - Get/set ctl-break check state & get boot drive
   34 - Get address to DOS critical flag (undocumented)
   35 - Get vector
   36 - Get disk free space
   37 - Get/set switch character (undocumented)
   38 - Get/set country dependent information
   39 - Create subdirectory (mkdir)
   3A - Remove subdirectory (rmdir)
   3B - Change current subdirectory (chdir)
   3C - Create file using handle
   3D - Open file using handle
   3E - Close file using handle
   3F - Read file or device using handle
   40 - Write file or device using handle
   41 - Delete file
   42 - Move file pointer using handle
   43 - Change file mode
   44 - I/O control for devices
   45 - Duplicate file handle
   46 - Force duplicate file handle
   47 - Get current directory
   48 - Allocate memory blocks
   49 - Free allocated memory blocks
   4A - Modify allocated memory blocks
   4B - EXEC load and execute program (func 1 undocumented)
   4C - Terminate process with return code
   4D - Get return code of a sub-process
   4E - Find first matching file
   4F - Find next matching file
   50 - Set current process id (undocumented)
   51 - Get current process id (undocumented)
   52 - Get pointer to DOS "INVARS" (undocumented)
   53 - Generate drive parameter table (undocumented)
   54 - Get verify setting
   55 - Create PSP (undocumented)
   56 - Rename file
   57 - Get/set file date and time using handle
   58 - Get/set memory allocation strategy (3.x+, undocumented)
   59 - Get extended error information (3.x+)
   5A - Create temporary file (3.x+)
   5B - Create new file (3.x+)
   5C - Lock/unlock file access (3.x+)
   5D - Critical error information (undocumented)
   5E - Network services (3.1+)
   5F - Network redirection (3.1+)
   60 - Get fully qualified file name (undocumented 3.x+)
   62 - Get address of program segment prefix (3.x+)
   63 - Get system lead byte table (MSDOS 2.25 only)
   64 - Set device driver look ahead  (undocumented 3.3+)
   65 - Get extended country information (3.3+)
   66 - Get/set global code page (3.3+)
   67 - Set handle count (3.3+)
   68 - Flush buffer (3.3+)
   69 - Get/set disk serial number (undocumented DOS 4.0+)
   6A - DOS reserved (DOS 4.0+)
   6B - DOS reserved
   6C - Extended open/create (4.x+)
   F8 - Set OEM INT 21 handler (functions F9-FF) (undocumented)


%FCB related DOS functions:

    F - Open file using FCB
   10 - Close file using FCB
   11 - Search for first entry using FCB
   12 - Search for next entry using FCB
   13 - Delete file using FCB
   14 - Sequential read using FCB
   15 - Sequential write using FCB
   16 - Create a file using FCB
   17 - Rename file using FCB
   21 - Random read using FCB
   22 - Random write using FCB
   23 - Get file size using FCB
   24 - Set relative record field for FCB
   27 - Random block read using FCB
   28 - Random block write using FCB
   29 - Parse filename for FCB


%Handle and Non-FCB related DOS function calls:

   3C - Create file using handle
   3D - Open file using handle
   3E - Close file using handle
   3F - Read file or device using handle
   40 - Write file or device using handle
   41 - Delete file
   42 - Move file pointer using handle
   43 - Change file mode
   45 - Duplicate file handle
   46 - Force duplicate file handle
   56 - Rename file
   57 - Get/set file date and time using handle
   5A - Create temporary file (3.x+)
   5B - Create new file (3.x+)
   67 - Set handle count (3.3+)
   68 - Flush buffer (3.3+)


 - int 21 functions are called with the function number in AH
 - register AX may be altered, its contents are not guaranteed
 - if an error occurs, CF is set to 1 and AX contains a simple
   error code;   INT 21,59 can be used to determine cause.
 - most INT 21 functions do not restore the flags to pre-interrupt
   state to allow returning of information via the flags register

:int 21,0
^INT 21,0 - Program Terminate


 AH = 00
 CS = PSP segment address


 returns nothing


 - restores the terminate, ctl-break, and critical error
   exit addresses, flushes all buffers, frees memory
   and returns to DOS via the termination handler address
 - does not close FCBs
 - this function is no longer recommended, but can be used by
   version of DOS before 2.0


 - see   INT 21,4C   INT 20

:int 21,1
^INT 21,1 - Keyboard Input with Echo


 AH = 01


 on return:
 AL = character from standard input device


 - waits for keyboard input from STDIN and echoes to STDOUT
 - returns 0 for extended keystroke, then function must be
   called again to return scan code
 - if Ctrl-Break is detected, INT 23h is executed

:int 21,2
^INT 21,2 - Display Output


 AH = 02
 DL = character to output


 returns nothing


 - outputs character to STDOUT
 - backspace is treated as non-destructive cursor left
 - if Ctrl-Break is detected, INT 23h is executed

:int 21,3
^INT 21,3 - Wait for Auxiliary Device Input


 AH = 03


 on return:
 AL = character from the auxiliary device


 - does not supply error returns
 - waits for character and reads from STDAUX
 - default DOS AUX parameters are 2400,N,8,1

:int 21,4
^INT 21,4 - Auxiliary Output


 AH = 04
 DL = character to output


 returns nothing


 - sends character in DL to STDAUX
 - does not supply error returns
 - waits until STDAUX is available
 - default DOS AUX parameters are 2400,N,8,1

:int 21,5
^INT 21,5 - Printer Output


 AH = 05
 DL = character to output


 returns nothing


 - sends character in DL to STDPRN
 - waits until STDPRN device is ready before output

:int 21,6
^INT 21,6 - Direct Console I/O

 AH = 06
 DL = (0-FE) character to output
    = FF if console input request

 on return:
 AL = input character if console input request (DL=FF)
 ZF = 0  if console request character available (in AL)
    = 1  if no character is ready, and function request
      was console input


 - reads from or writes to the console device depending on
   the value of DL
 - cannot output character FF  (DL=FF indicates read function)
 - for console read, no echo is produced
 - returns 0 for extended keystroke, then function must be
   called again to return scan code
 - ignores Ctrl-Break and Ctrl-PrtSc

:int 21,7
^INT 21,7 - Direct Console Input Without Echo


 AH = 07


 on return:
 AL = character from STDIN


 - waits for keyboard input until keystroke is ready
 - character is not echoed to STDOUT
 - returns 0 for extended keystroke, then function must be
   called again to return scan code
 - ignores Ctrl-Break and Ctrl-PrtSc
 - see   INT 21,1

:int 21,8
^INT 21,8 - Console Input Without Echo


 AH = 08


 on return:
 AL = character from STDIN


 - returns 0 for extended keystroke, then function must be
   called again to return scan code
 - waits for character from STDIN and returns data in AL
 - if Ctrl-Break is detected, INT 23h is executed

:int 21,9
^INT 21,9 - Print String


 AH = 09
 DS:DX = pointer to string ending in "$"


 returns nothing


 - outputs character string to STDOUT up to "$"
 - backspace is treated as non-destructive
 - if Ctrl-Break is detected, INT 23h is executed

:int 21,a
^INT 21,A - Buffered Keyboard Input

 AH = 0A
 DS:DX = pointer to input buffer of the format:

 │ max │ count │  BUFFER (N bytes)
    │      │          └────── input buffer
    │      └──────────── number of characters returned (byte)
    └────────────── maximum number of characters to read (byte)


 returns nothing

 - since strings can be pre-loaded, it is recommended that the
   default string be terminated with a CR
 - N bytes of data are read from STDIN into buffer+2
 - max buffer size is 255, minimum buffer size is 1 byte
 - chars up to and including a CR are placed into the buffer
   beginning at byte 2;  Byte 1 returns the number of chars
   placed into the buffer  (extended codes take 2 characters)
 - DOS editing keys are active during this call
 - INT 23 is called if Ctrl-Break or Ctrl-C detected

:int 21,b
^INT 21,B - Check Standard Input Status


 AH = 0B


 on return:
 AL = 00 if no character available
    = FF if character available


 - checks STDIN for available characters
 - character is not returned
 - if Ctrl-Break is detected INT 23h is executed

:int 21,c
^INT 21,C - Clear Keyboard Buffer and Invoke Keyboard Function


 AH = 0C
 AL = 01, 06, 07, 08 or 0A   (INT 21 input functions)


 on return:
 see return values from INT 21,AL where AL is 1, 6, 7, 8 or A


 - main function is to clear the input buffer and call INT 21h with
   the specified function (in AL)
 - see   INT 21

:int 21,d
^INT 21,D - Disk Reset


 AH = 0D


 returns nothing


 - all file buffers are flushed to disk
 - does NOT update directory entry

:int 21,e
^INT 21,E - Select Disk


 AH = 0E
 DL = zero based, drive number (0-25, A: - Z:)


 on return:
 AL = one based, total number of logical drives including
      hardfiles (1-26)


 - for DOS 3.x+, this function returns the number of logical
   drives or the value of LASTDRIVE (default of 5) in the
   CONFIG.SYS file

:int 21,f
^INT 21,F - Open a File Using FCB

 AH = 0F
 DS:DX = pointer to unopened FCB


 on return:
 AL = 00 if file opened
    = FF if unable to open


 - opens an existing file using a previously setup FCB
 - the FCB fields drive identifier, filename and extension
   must be filled in before call
 - sets default FCB fields; current block number is set to 0;
   record size is set to 80h; file size, date and time are set
   to the values from the directory
 - does not create file, see  INT 21,16
 - DOS 2.x allows opening of subdirectories, DOS 3.x does not

 - see   FCB
:int 21,10
^INT 21,10 - Close a File Using FCB


 AH = 10h
 DS:DX = pointer to opened FCB


 on return:
 AL = 00  if file closed
    = FF  if file not closed


 - closes a previously opened file opened with an FCB
 - FCB must be setup with drive id, filename, and extension
   before call

:int 21,11
^INT 21,11 - Search for First Entry Using FCB

 AH = 11h
 DS:DX = pointer to unopened FCB

 on return:
 AL = 00 if matching file found
    = FF if file not found

 - searches for first occurrence of filename specified in FCB
 - FCB must have drive id, filename, and extension before call
 - extended FCB can be used to specify a search criteria based
   on attributes; hidden, system, label, and directory attributes
   can be used to narrow the search  (see FILE ATTRIBUTES)
 - after successful call DTA holds an unopened FCB/XFCB for
   the requested file.   Using any of the other FCB functions
   destroys this DTA copy of the FCB/XFCB
 - searching can be continued with the FCB find-next function
 - "?" wildcard supported after DOS 2.1, "*" supported in DOS 3.x
 - DOS 2.x can't find . and .. entries, DOS 3.x can (unless in root)
 - see   INT 21,12   FCB   XFCB   FILE ATTRIBUTES

:int 21,12
^INT 21,12 - Search for Next Entry Using FCB

 AH = 12h
 DS:DX = pointer to unopened FCB returned from
         INT 21,11  or  INT 21,12


 on return:
 AL = 00 if file found
    = FF if file not found


 - finds next matching file after calls to INT 21,11 and
   INT 21,12
 - FCB should be the same across calls to INT 21,11 and 12
 - after successful call DTA holds an unopened FCB/XFCB for
   the requested file.   Using any of the other FCB functions
   destroys this DTA copy of the FCB/XFCB

 - see   FCB   XFCB
:int 21,13
^INT 21,13 - Delete File Using FCB


 AH = 13h
 DS:DX = pointer to an unopened FCB


 on return:
 AL = 00 if file deleted
    = FF if file not found


 - deletes unopened file with normal attributes
 - FCB must contain drive id, filename, and extension before call
 - "?" wildcard supported after DOS 2.1, "*" supported by DOS 3.x+
 - DOS 2.x allowed deletion of a subdirectory if XFCB was provided,
   even if files existed, causing lost clusters.  DOS 3.x does not

 - see   FCB   XFCB

:int 21,14
^INT 21,14 - Sequential Read Using FCB

 AH = 14h
 DS:DX = pointer to an opened FCB


 on return:
 AL = 00 if successful read
    = 01 if end of file (no data read)
    = 02 if DTA is too small
    = 03 if end of file or partial record read


 - reads a record from file pointed to by FCB at the location
   specified in current block and current record number
 - data record is read into the DTA
 - FCB record number is updated

 - see   FCB   XFCB
:int 21,15
^INT 21,15 - Sequential Write Using FCB


 AH = 15h
 DS:DX = pointer to an opened FCB


 on return:
 AL = 00 if write was successful
    = 01 if diskette is full or read only
    = 02 if DTA is too small


 - writes a record from the DTA to the current record position
   in file specified by the opened FCB
 - record size and output location are maintained in the FCB

 - see   FCB   XFCB

:int 21,16
^INT 21,16 - Create a File Using FCB


 AH = 16h
 DS:DX = pointer to an unopened FCB


 on return:
 AL = 00 if file created
    = FF if file creation failed


 - creates file using FCB and leaves open for later output
 - FCB must be setup with drive id, filename, and extension
   before call
 - an extended FCB can be used to also set file attributes

 - see   FCB   XFCB

:int 21,17
^INT 21,17 - Rename a File Using FCB

 AH = 17h
 DS:DX = pointer to a modified FCB of the format:

   Offset     Description
     00     drive designator
     01     original file name
     09     original file extension
     11     new file name
     19     new extension


 on return:
 AL = 00 if file renamed
    = FF if file not renamed


 - allows renaming of files with normal attributes
 - "?" wildcard supported after DOS 2.1, "*" supported by
   DOS 3.x+
:int 21,19
^INT 21,19 - Get Current Default Drive


 AH = 19h


 on return:
 AL = current default drive (0=A,1=B,etc)


 - determines the current default drive

:int 21,1a
^INT 21,1A - Set Disk Transfer Address (DTA)


 AH = 1A
 DS:DX = pointer to disk transfer address


 returns nothing


 - specifies the disk transfer address to DOS
 - DTA cannot overlap 64K segment boundary
 - offset 80h in the PSP is a 128 byte default DTA supplied
   by DOS upon program load
 - use of the DTA provided by DOS will result in the loss
   of the program command tail which also occupies the 128
   bytes starting at offset 80h of the PSP

:int 21,1b
^INT 21,1B - Get Allocation Table Information


 AH = 1B


 on return:
 AL = sectors per cluster
 CX = bytes per sector
 DX = clusters on disk
 DS:BX = pointer to Media Descriptor Byte found in FAT


 - retrieves information on capacity and format of default drive
 - DS:BX can be used to determine if drive is RAMDISK or removable
 - see   MEDIA DESCRIPTOR BYTE   INT 21,1C

:int 21,1c
^INT 21,1C - Get Allocation Table Info for Specified Drive


 AH = 1C
 DL = drive number (0 for default, 1 = A:, Z: = 26)


 on return:
 AL = sectors per cluster
 CX = bytes per sector
 DX = clusters on disk
 DS:BX = pointer to Media Descriptor Byte found in FAT


 - retrieves information on capacity and format of specified drive
 - DS:BX can be used to determine if drive is RAMDISK or removable
 - see   MEDIA DESCRIPTOR BYTE   INT 21,1B

:int 21,1f
^INT 21,1F - Get Pointer to Current Drive Parameter Table
^(Undocumented)


 AH = 1F
 DL = drive number (0=default, 1=A, ...)


 on return:
 AL = 00 - DS:BX is pointer to drive parameter table  (DPT)
      FF - drive does not exist
 DS:BX = pointer to drive parameter table (DPT) if AL=0


 - the format of the DPT varies between DOS versions


 - see   DPT   UNDOC

:int 21,21
^INT 21,21 - Random Read Using FCB


 AH = 21h
 DS:DX = pointer to an opened FCB


 on return:
 AL = 00 if read successful
    = 01 if EOF (no data read)
    = 02 if DTA is too small
    = 03 if EOF (partial record read)


 - reads random records from a file opened with an FCB
   to the DTA
 - FCB must be setup with drive id, filename, extension,
   record position and record length before call
 - current record position field in FCB is not updated

:int 21,22
^INT 21,22 - Random Write Using FCB


 AH = 22h
 DS:DX = far pointer to an opened FCB


 on return:
 AL = 00 if write successful
    = 01 if diskette full or read only
    = 02 if DTA is too small


 - write records to random location in file opened with FCB
 - FCB must be setup with drive id, filename, extension,
   record position and record length before call
 - current record position field in FCB is not updated

:int 21,23
^INT 21,23 - Get File Size Using FCB


 AH = 23h
 DS:DX = pointer to an unopened FCB


 on return:
 AL = 00 if successful
    = FF if file not found


 - determines the number of records in a file
 - FCB must be setup with drive id, complete filename and
   extension plus record length before call
 - updates random record position in FCB located at DS:DX
   with file record count

:int 21,24
^INT 21,24 - Set Relative Record Field in FCB


 AH = 24h
 DS:DX = pointer to an opened FCB


 returns nothing


 - modifies opened FCB for random operation
 - sets FCB random record field to current sequential block
   and record fields

:int 21,25
^INT 21,25 - Set Interrupt Vector


 AH = 25h
 AL = interrupt number
 DS:DX = pointer to interrupt handler


 returns nothing


 - provides a safe method for changing interrupt vectors


 - see   INT 21,35

:int 21,26
^INT 21,26 - Create New Program Segment Prefix


 AH = 26h
 DX = segment address of new PSP


 returns nothing


 - allocates memory for a PSP and copies current PSP there
 - used before DOS 2.x to spawn a child process
 - the application is responsible for allocating any memory
   necessary for the child process
 - INT 21,4B (EXEC) is now the recommended method for starting
   a child process, so this function should be avoided


 - see   INT 21,4B   INT 21,55   EXEC...   SPAWN...

:int 21,27
^INT 21,27 - Random Block Read Using FCB


 AH = 27h
 CX = number of records to read
 DS:DX = pointer to an opened FCB


 on return:
 AL = 00 if read was successful
    = 01 if EOF (no data read)
    = 02 if DTA is too small
    = 03 if EOF (partial record read)
 CX = actual number of records read


 - allows random access and sequential reading of a group
   of records from a file opened with an FCB into the DTA
 - FCB must be setup with drive id, filename, extension
   record length and random record number before call

:int 21,28
^INT 21,28 - Random Block Write Using FCB


 AH = 28h
 CX = number of records to write
 DS:DX = pointer to an opened FCB


 on return:
 AL = 00 if write successful
    = 01 if diskette full or read only
    = 02 if DTA is too small
 CX = number of records written


 - allows random access and sequential writing of a group
   of records from a file opened with an FCB into the DTA
 - FCB must be setup with random record number and record size
 - updates random record number, current block and current
   record fields

:int 21,29
^INT 21,29 - Parse a Filename for FCB

 AH = 29h
 AL = bit pattern to control parsing (see bit meanings below)
 DS:SI = pointer to a command line to parse
 ES:DI = pointer to a buffer for unopened FCB


 Bit patterns for parsing control found in AL:

 │7│6│5│4│3│2│1│0│  AL
  │ │ │ │ │ │ │ └──── 1 = ignore leading separators
  │ │ │ │ │ │ │       0 = don't ignore leading separators
  │ │ │ │ │ │ └───── 1 = modify drive ID if specified
  │ │ │ │ │ │        0 = modify drive ID regardless
  │ │ │ │ │ └────── 1 = modify filename if specified
  │ │ │ │ │         0 = modify filename regardless
  │ │ │ │ └─────── 1 = modify extension if specified
  │ │ │ │          0 = modify extension regardless
  └─┴─┴─┴──────── unused

 on return:
 AL = 00 if no wildcard characters present
    = 01 if wildcards present in string
    = FF if drive specifier is invalid
 DS:SI = pointer to the first character after parsed filename
 ES:DI = pointer to the updated unopened FCB


 - retrieves filename from the command line string and places
   the filename components into an unopened FCB for later use
 - if no filename is found a pointer is returned in ES:DI that
   has a blank at ES:DI+1

:int 21,2a
^INT 21,2A - Get Date


 AH = 2A


 on return:
 AL = day of the week (0=Sunday)
 CX = year (1980-2099)
 DH = month (1-12)
 DL = day (1-31)


 - retrieves system date based on the DOS maintained clock

:int 21,2b
^INT 21,2B - Set Date


 AH = 2B
 CX = year (1980-2099)
 DH = month (1-12)
 DL = day (1-31)


 on return:
 AL = 00 if date change successful
    = FF if invalid date


 - sets DOS maintained clock
 - DOS version 3.3+ also update CMOS date where applicable

:int 21,2c
^INT 21,2C - Get Time


 AH = 2C


 on return:
 CH = hour (0-23)
 CL = minutes (0-59)
 DH = seconds (0-59)
 DL = hundredths (0-99)


 - retrieves DOS maintained clock time

:int 21,2d
^INT 21,2D - Set Time


 AH = 2D
 CH = hour (0-23)
 CL = minutes (0-59)
 DH = seconds (0-59)
 DL = hundredths (0-99)


 on return:
 AL = 00 if time change successful
    = FF if time invalid


 - changes DOS maintained clock
 - DOS version 3.3+ also update CMOS clock where applicable

:int 21,2e
^INT 21,2E - Set/Reset Verify Switch


 AH = 2E
 AL = 00 to set off
    = 01 to set verify on
 DH = 00 for DOS versions before 3.0


 returns nothing


 - with the verify setting on, disk I/O is more secure but
   takes longer to complete


 - see   INT 21,54

:int 21,2f
^INT 21,2F - Get Disk Transfer Address (DTA)


 AH = 2F


 on return:
 ES:BX = pointer to current DTA


 - returns the DTA address
 - the default DTA is a 128 byte block at address 80h in the
   Program Segment Prefix (PSP).  This area also contains the
   command tail at program startup it must be saved or the DTA
   must be relocated before use to preserve the command tail

 - see   INT 21,1A   DTA

:int 21,30
^INT 21,30 - Get DOS Version Number


 AH = 30h


 on return:
 AL = major version number (2-5)
 AH = minor version number (in hundredths)
 BX = 0
 CX = 0


 - for an example DOS version 2.1 returns AL=2 and AH=10
 - DOS versions prior to DOS 2.0 return zero in AH and AL
 - DOS version 4.0 and 4.1 usually return the same value of 4.00

:int 21,31
^INT 21,31 - Terminate Process and Remain Resident


 AH = 31h
 AL = exit code (returned to batch files)
 DX = memory size in paragraphs to reserve


 returns nothing


 - preferred method for Terminate and Stay Resident programs
 - terminates process without releasing allocated memory and
   without closing open files
 - attempts allocation of memory specified in DX from memory
   allocated by DOS at startup.   INT 21,48 memory allocation
   is not affected

 - see   INT 27

:int 21,32
^INT 21,32 - Get Pointer to Drive Parameter Table (Undocumented)

 AH = 32h
 DL = drive (0=default, 1=A:, 2=B:, 3=C:, ...)


 on return:
 AL =  FF if the drive number in DL was invalid
 DS:BX = address of drive parameter table (DPT)


 - available since DOS 2.0
 - used by DOS commands CHKDSK and RECOVER
 - forces a media check, which clears byte DS:[BX+17h] or
   DS:[BX+18h] in the Drive Parameter Table
 - actually accesses the disk, causing a critical error if a
   disk error occurs
 - can be used to determine if a drive is SUBST'ed by comparing
   DS:[BX+1] and DS:[BX] for a match.  If not equal, then the
   drive is possibly SUBST'ed (though not guaranteed)
   (may also indicate a Bernoulli box)
 - can be used to determine if a drive is a RAM disk;
   if (DS:[BX] != DS:[BX+1]) and (DS:[BX+1] == 0), then the disk
   is possibly a RAM disk (not guaranteed)

 - see   DPT   UNDOC

:int 21,33
^INT 21,33 - Get/Set System Values (Ctl-Break/Boot Drive)


 AH = 33h
 AL = 00 to get current Ctrl-Break flag
    = 01 to set current Ctrl-Break flag
    = 05 get boot drive (DOS 4.x)
 DL = 00 to set Ctrl-Break checking off
    = 01 to set Ctrl-Break checking on
    = boot drive for subfunction 5;  (1=A:, 2=B:, ...)


 on return:
 DL = 00 Ctrl-Break checking OFF (AL=0)
    = 01 Ctrl-Break checking ON  (AL=0)
    = boot drive number (1-26, A: - Z:) (function 05)


 - retrieves DOS Ctrl-Break setting which determines if DOS
   will check for Ctrl-Break during INT 21 functions

:int 21,34:indos
^INT 21,34 - Get Address to DOS Critical Flag
^INDOS  (Undocumented)

 AH = 34h

 on return:
 ES:BX = address of a byte indicating whether a DOS call is
         in progress.  No DOS calls should be made if set.


 - AKA the INDOS flag, this critical section flag may be
   checked from within an interrupt handler before requesting
   a DOS service.   It is a semaphore that is non-zero when
   DOS is busy, and zero if DOS is free.
 - though this flag indicates whether a DOS interrupt is active,
   it should not be used alone to determine DOS is safe for re-entry
 - this interrupt should be used only during TSR initialization;
   the returned pointer should be used thereafter
 - this flag is cleared by a critical error (INT 24)
 - ES:BX-1 points to the critical error flag for DOS 3.x+
   ES:BX+1 points to the critical error flag for DOS 2.x
   ES:BX-1AA points to the critical error flag for COMPAQ DOS 3.0

 - see   UNDOC   INVARS   INT 21,52   INT 21,5D

:int 21,35
^INT 21,35 - Get Interrupt Vector


 AH = 35h
 AL = interrupt vector number


 on return:
 ES:BX = pointer to interrupt handler


 - standard method for retrieving interrupt vectors


 - see   INT 21,25

:int 21,36
^INT 21,36 - Get Disk Free Space


 AH = 36h
 DL = drive number (0=default, 1=A:)


 on return:
 AX = sectors per cluster
    = FFFF if drive is invalid
 BX = number of available clusters
 CX = number of bytes per sector
 DX = number of clusters per drive


 - used to determine available space on specified disk
 - see   INT 21,1B   INT 21,1C

:int 21,37
^INT 21,37 - Get/Set Switch Character (Undocumented)


 AH = 37h
 AL = 0  get switch character into DL;  some systems return "-"
    = 1  set switch character to value in DL
    = 2  read device prefix flag into DL;  returns DL = 0 indicating
         devices must be accessed using /DEV/device. A non-zero value
         indicates devices are accessible without prefix
    = 3  set device prefix flag (DOS 2.x).  All device names must
         begin with \DEV\.
         DL = 0 clears flag
            = 1 sets flag

 on return:
 AL = FF  illegal function code specified


 - formerly available as a CONFIG.SYS command (DOS before 3.x)
 - see  UNDOC


:int 21,38
^INT 21,38 - Get/Set Country Dependent Information

 AH = 38h
 AL = 00 to get current country information
    = 00-FE country codes  (DOS 3.x+)
    = FF for country codes >= FF, country codes are in BX
 BX = country code if AL = FF (country code > 255)
 DX = FFFF to set country information
 DS:DX = pointer to buffer to contain country data (if get data)

 on return:
 AX = error code if CF set
    = 02 invalid country
 BX = country code (DOS 3.x+)
 DS:DX = pointer to returned country data (see COUNTRY CODES)


 - returns a pointer to country specific data, for DOS 3.x+ this
   function can be used to also set this information

 - see   COUNTRY CODES

:int 21,39
^INT 21,39 - Create Subdirectory (mkdir)


 AH = 39h
 DS:DX = pointer to ASCIIZ path name


 on return:
 CF = 0 if successful
    = 1 if error
 AX = error code  (see DOS ERROR CODES)


 - creates specified subdirectory
 - returns error if directory already exists, element of the path
   is not found, directory full or write protected disk

:int 21,3a
^INT 21,3A - Remove Subdirectory (rmdir)


 AH = 3A
 DS:DX = pointer to ASCIIZ path name


 on return:
 CF = 0 if successful
    = 1 if error
 AX = error code  (see DOS ERROR CODES)


 - allows deletion of a subdirectory as long as it exists, is empty
   and not the current directory

:int 21,3b
^INT 21,3B - Change Current Directory (chdir)


 AH = 3B
 DS:DX = pointer to ASCIIZ path name


 on return:
 CF = 0 if successful
    = 1 if error
 AX = error code if CF set  (see DOS ERROR CODES)


 - changes the current directory to the directory specified
   by pointer DS:DX

:int 21,3c
^INT 21,3C - Create File Using Handle


 AH = 3C
 CX = file attribute  (see FILE ATTRIBUTES)
 DS:DX = pointer to ASCIIZ path name


 on return:
 CF = 0 if successful
    = 1 if error
 AX = files handle if successful
    = error code if failure  (see DOS ERROR CODES)


 - if file already exists, it is truncated to zero bytes on opening

:int 21,3d
^INT 21,3D - Open File Using Handle

 AH = 3D
 AL = open access mode
      00  read only
      01  write only
      02  read/write
 DS:DX = pointer to an ASCIIZ file name

 on return:
 AX = file handle if CF not set
    = error code if CF set  (see DOS ERROR CODES)


%Access modes in AL:

 │7│6│5│4│3│2│1│0│  AL
  │ │ │ │ │ └─┴─┴──── read/write/update access mode
  │ │ │ │ └───────── reserved, always 0
  │ └─┴─┴────────── sharing mode (see below) (DOS 3.1+)
  └─────────────── 1 = private, 0 = inheritable (DOS 3.1+)


%Sharing mode bits (DOS 3.1+):          Access mode bits:
%654                                    210
 000  compatibility mode (exclusive)    000  read access
 001  deny others read/write access     001  write access
 010  deny others write access          010  read/write access
 011  deny others read access
 100  full access permitted to all


 - will open normal, hidden and system files
 - file pointer is placed at beginning of file

:int 21,3e
^INT 21,3E - Close File Using Handle


 AH = 3E
 BX = file handle to close


 on return:
 AX = error code if CF set  (see DOS ERROR CODES)


 - if file is opened for update, file time and date stamp
   as well as file size are updated in the directory
 - handle is freed

:int 21,3f
^INT 21,3F - Read From File or Device Using Handle


 AH = 3F
 BX = file handle
 CX = number of bytes to read
 DS:DX = pointer to read buffer


 on return:
 AX = number of bytes read is CF not set
    = error code if CF set  (see DOS ERROR CODES)


 - read specified number of bytes from file into buffer DS:DX
 - when AX is not equal to CX then a partial read occurred due
   to end of file
 - if AX is zero, no data was read, and EOF occurred before read

:int 21,40
^INT 21,40 - Write To File or Device Using Handle


 AH = 40h
 BX = file handle
 CX = number of bytes to write
 DS:DX = pointer to write buffer


 on return:
 AX = number of bytes written if CF not set
    = error code if CF set  (see DOS ERROR CODES)



 - if AX is not equal to CX on return, a partial write occurred

:int 21,41
^INT 21,41 - Delete File


 AH = 41h
 DS:DX = pointer to an ASCIIZ filename


 on return:
 AX = error code if CF set  (see DOS ERROR CODES)


 - marks first byte of file directory entry with E5 to indicate
   the file has been deleted.  The rest of the directory entry
   stays intact until reused.   FAT pointers are returned to DOS
 - does not accept wildcard in filename

:int 21,42
^INT 21,42 - Move File Pointer Using Handle


 AH = 42h
 AL = origin of move:
      00 = beginning of file plus offset  (SEEK_SET)
      01 = current location plus offset  (SEEK_CUR)
      02 = end of file plus offset  (SEEK_END)
 BX = file handle
 CX = high order word of number of bytes to move
 DX = low order word of number of bytes to move


 on return:
 AX = error code if CF set  (see DOS ERROR CODES)
 DX:AX = new pointer location if CF not set


 - seeks to specified location in file
 - see   LSEEK   FSEEK

:int 21,43
^INT 21,43 - Get/Set File Attributes

 AH = 43h
 AL = 00 to get attribute
    = 01 to set attribute
 DS:DX = pointer to an ASCIIZ path name
 CX = attribute to set

 │5│4│3│2│1│0│  CX  valid file attributes
  │ │ │ │ │ └──── 1 = read only
  │ │ │ │ └───── 1 = hidden
  │ │ │ └────── 1 = system
  │ └─┴─────── not used for this call
  └────────── 1 = archive


 on return:
 AX = error code if CF set  (see DOS ERROR CODES)
 CX = the attribute if AL was 00

 - see   DIRECTORY

:int 21,44
^INT 21,44 - I/O Control for Devices  (IOCTL)

%Standard Call Format

 AH = 44h
 AL = function value
 BX = file handle
 BL = logical device number (0=default, 1=A:, 2=B:, 3=C:, ...)
 CX = number of bytes to read or write
 DS:DX = data or buffer


 on return:
 AX = error code if CF set
 AX = # of bytes transferred if CF not set


%See  IOCTL,n   where "n" is one of the following functions:

  0    Get Device Information
  1    Set Device Information
  2    Read From Character Device
  3    Write to Character Device
  4    Read From Block Device
  5    Write to Block Device
  6    Get Input Status
  7    Get Output Status
  8    Device Removable Query
  9    Device Local or Remote Query
  A    Handle Local or Remote Query
  B    Set Sharing Retry Count
  C    Generic I/O for Handles
  D    Generic I/O for Block Devices (3.2+)
  E    Get Logical Drive (3.2+)
  F    Set Logical Drive (3.2+)


 - see:  DEVICE COMMAND CODES
         DEVICE REQUEST HEADER
         DEVICE STATUS
         DEVICE HEADER
         DEVICE ATTRIBUTES

:int 21,44,0:ioctl,0
^INT 21,44,0 / IOCTL,0 - Get Device Information

 AH = 44h
 AL = 00
 BX = handle (must be an opened device)


 on return
 AX = error code if CF set  (see DOS ERROR CODES)
 DX = device information  (see tables below)


 │F│E│D│C│B│A│9│8│7│6│5-0│  Block Device Information
  │ │ │ │ │ │ │ │ │ │  └───── drive number (0=A:,1=B:)
  │ │ │ │ │ │ │ │ │ └─────── 0 = file has been written
  │ │ │ │ │ │ │ │ └─────── 0 = disk file
  └─┴─┴─┴─┴─┴─┴─┴─────── reserved, must be zero

 │F│E│D-8│7│6│5│4│3│2│1│0│  Character Device Information
  │ │  │  │ │ │ │ │ │ │ └──── 1 = standard input device
  │ │  │  │ │ │ │ │ │ └──── 1 = standard output device
  │ │  │  │ │ │ │ │ └──── 1 = NUL device
  │ │  │  │ │ │ │ └──── 1 = clock device
  │ │  │  │ │ │ └──── reserved
  │ │  │  │ │ └──── 1 = binary mode, 0 = translated
  │ │  │  │ └──── 0 = end of file on input
  │ │  │  └──── 1 = character device, 0 if disk file
  │ │  └───── reserved, see DEVICE ATTRIBUTES
  │ └────── 1 = supports IOCTL, via functions 2 & 3
  └────── reserved


 - BIT 7 of register DX can be used to detect if STDIN/STDOUT is
   redirected to/from disk; if a call to this function has DX BIT 7
   set it's not redirected from/to disk; if it's clear then it is
   redirected to/from disk

:int 21,44,1:ioctl,1
^INT 21,44,1 / IOCTL,1 - Set Device Information

 AH = 44h
 AL = 01
 BX = handle
 DH = must be zero
 DL = device data low order byte  (see below)


 on return
 AX = error code if CF set
 DX = device information  (see below)


 - applicable to character devices only
 - allows setting of device data word for character devices
 - usually used to change from binary to translated I/O
 - handle in BX must be an opened file or device


^Device Data Word

 │F│E│D│C│B│A│9│8│7│6│5│4│3│2│1│0│  Device Data Word
  │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ └──── 1 = standard input device
  │ │ │ │ │ │ │ │ │ │ │ │ │ │ └──── 1 = standard output device
  │ │ │ │ │ │ │ │ │ │ │ │ │ └──── 1 = NUL device
  │ │ │ │ │ │ │ │ │ │ │ │ └──── 1 = clock device
  │ │ │ │ │ │ │ │ │ │ │ └──── reserved
  │ │ │ │ │ │ │ │ │ │ └──── 1 = binary mode, 0 = translated
  │ │ │ │ │ │ │ │ │ └──── 0 = end of file on input
  │ │ │ │ │ │ │ │ └──── 1 = character device
  └─┴─┴─┴─┴─┴─┴─┴──── reserved, must be zero


:int 21,44,2:ioctl,2
^INT 21,44,2 / IOCTL,2 - Read From Character Device


 AH = 44h
 AL = 02
 BX = handle
 CX = number of bytes to read
 DS:DX = pointer to data buffer


 on return
 AX = number of bytes read if CF clear
    = error code if CF set   (see DOS ERROR CODES)


 - see bit 14 if IOCTL function 00h to determine if
   driver can support IOCTL control strings

:int 21,44,3:ioctl,3
^INT 21,44,3 / IOCTL,3 - Write to Character Device


 AH = 44h
 AL = 03
 BX = handle
 CX = number of bytes to send
 DS:DX = pointer to data buffer


 on return
 AX = number of bytes written if CF clear
    = error code if CF set   (see DOS ERROR CODES)


 - see bit 14 if IOCTL function 00h to determine if
   driver can support IOCTL control strings

:int 21,44,4:ioctl,4
^INT 21,44,4 / IOCTL,4 - Read from Block Device


 AH = 44h
 AL = 04
 BL = drive number (0=default, 1=A:, 2=B:, 3=C:, ...)
 CX = number of bytes to read
 DS:DX = pointer to data buffer


 on return
 AX = number of bytes read if CF clear
    = error code if CF set  (see DOS ERROR CODES)


 - block drivers are not required to support this function
 - returns AX = 01 (invalid function code) if not supported

:int 21,44,5:ioctl,5
^INT 21,44,5 / IOCTL,5 - Write to Block Device


 AH = 44h
 AL = 05
 BL = drive number (0=default, 1=A:, 2=B:, 3=C:, ...)
 CX = number of bytes to send
 DS:DX = pointer to data buffer


 on return
 AX = number of bytes written if CF clear
    = error code if CF set  (see DOS ERROR CODES)


 - block devices are not required to support this function
 - returns AX = 01 (invalid function code) if not supported

:int 21,44,6:ioctl,6
^INT 21,44,6 / IOCTL,6 - Get Input Status


 AH = 44h
 AL = 06
 BX = handle


 on return
 CF = 0 if successful
    = 1 if error
 AX = error code if CF set  (see DOS ERROR CODES)
 AL = 00  if EOF (files), or not ready (char devices)
    = FF  if not EOF (files), or ready (char devices)


 - used to determine if a file or device is ready for input
 - can be used to determine EOF unless EOF caused by INT 21,42

:int 21,44,7:ioctl,7
^INT 21,44,7 / IOCTL,7 - Get Output Status


 AH = 44h
 AL = 07
 BX = handle


 on return
 CF = 0 if successful
    = 1 if error
 AX = error code if CF set  (see DOS ERROR CODES)
 AL = 00  if ready (files), or not ready (char devices)
    = FF  ready (files or char device)


 - indicates if a device or file is ready for output
 - files always return ready, character devices don't

:int 21,44,8:ioctl,8
^INT 21,44,8 / IOCTL,8 - Device Removable Query

 AH = 44h
 AL = 08
 BL = drive number (0=default, 1=A:, 2=B:, 3=C:, ...)


 on return
 CF = 0 if successful
    = 1 if error
 AX = 00  removable media
    = 01  non-removable media
    = error code if CF set  (see DOS ERROR CODES)


 - used to determine if a device supports removable media
 - RAM disks are not considered removable media
 - device drivers compatible with DOS 2.0 do not always respond
   correctly to this query
 - implemented from DOS 3.0;  for earlier DOS versions drive A: and
   B: are removable media since DRIVER.SYS/SUBST are DOS 3.0+ only
:int 21,44,9:ioctl,9
^INT 21,44,9 / IOCTL,9 - Device Local or Remote Query


 AH = 44h
 AL = 09
 BL = drive number (0=default, 1=A:, 2=B:, 3=C:, ...)


 on return
 AX = error code if CF set  (see DOS ERROR CODES)
 DX = device attribute word
      bit 12 = 1 if drive is remote
      bit 12 = 0 if drive is local


 - used to determine if block device is local or remote
 - returns invalid function if networking not started
 - implemented from DOS 3.1

:int 21,44,a:ioctl,a
^INT 21,44,A / IOCTL,A - Handle Local or Remote Query


 AH = 44h
 AL = 0A
 BX = handle


 on return
 AX = error code if CF set  (see DOS ERROR CODES)
 DX = device attribute word
      bit 15 = 1 if drive is remote
      bit 15 = 0 if drive is local


 - used to determine if block device is local or remote
 - returns invalid function if networking not started
 - implemented from DOS 3.1

:int 21,44,b:ioctl,b
^INT 21,44,B / IOCTL,B - Set Sharing Retry Count


 AH = 44h
 AL = 0B
 CX = pause between retries  (default 1)
 DX = number of retries  (default 3)


 on return
 AX = error code if CF set  (see DOS ERROR CODES)


 - retry parameters are associated with file locking
 - differences in CPU and clock speeds affect length of pauses
 - requires SHARE be loaded or invalid function is returned
 - implemented from DOS 3.0

:int 21,44,c:ioctl,c
^INT 21,44,C / IOCTL,C - Generic I/O for Handles

 AH = 44h
 AL = 0C
 BX = handle
 CH = device type
    = 00  unknown device type  (DOS 3.3+)
    = 01  COMx  (DOS 3.3+)
    = 03  CON  (DOS 3.3+)
    = 05  LPTx  (DOS 3.3+),  printer  (DOS 3.2)
 CL = minor function code (when CH = 3 or CH = 5)
    = 45  set iteration count  (DOS 3.2 only)

    = 4A  select code page (DOS 3.3+); parameter format:
            00  word  length of data
            02  word  code page ID
            04 nwords character set data array (see offset 00)

    = 4C  code page prepare start  (DOS 3.3+); parameter format:
            00  word  flags
            02  word  length of remainder of parameter block
            04  word  number of code pages following
            06 nwords code page 1,...,N

    = 4D  code page prepare end  (DOS 3.3+); parameter format:
            00  word  length of data
            02  word  code page ID

    = 5F  set display info  (DOS 4.x, when CH=3); parameter format:
            00  byte  level  (0 for DOS 4.0)
            01  byte  reserved
            02  word  length of following data
            04  word  control flags
                      bit 0 set for blink, clear for intensity
                      bits 1 to 15 reserved
            06  byte  mode type (1=text, 2=graphics)
            07  byte  reserved
            08  word  colors;  0=monochrome, n=bits per pixel
            0A  word  pixel columns
            0C  word  pixel rows
            0E  word  character columns
            10  word  character rows

    = 65  get iteration count  (DOS 3.2 only)

    = 6A  query selected code page  (DOS 3.3+); parameter format:
            00  word  length of data
            02  word  code page ID
            04 nwords character set data array  (see offset 00)

    = 6B  query prepare list  (DOS 3.3+); Parameter format:
            00  word  length of following data
            02  word  number of hardware code pages
            04 nwords hardware code page array
            xx  word  number of prepared code pages
            xx nwords prepared code page array

    = 7F  get display info  (DOS 4.x, CH = 3)
            00  byte  level  (0 for DOS 4.0)
            01  byte  reserved
            02  word  length of following data
            04  word  control flags
                        bit 0 set for blink, clear for intensity
                        bits 1 to 15 reserved
            06  byte  mode type (1=text, 2=graphics)
            07  byte  reserved
            08  word  colors;  0=monochrome, n=bits per pixel
            0A  word  pixel columns
            0C  word  pixel rows
            0E  word  character columns
            10  word  character rows

 DS:DX = pointer to iteration count word  (DOS 3.2)
       = pointer to parameter block  (DOS 3.3)


 on return
 AX = error code if CF set  (see DOS ERROR CODES)


 - iteration count word specifies the number of times to retry
   an operation before aborting
 - DOS 3.3 changed this function to handle code page switching
 - implemented from DOS 3.2
 - DOS 4.x adds support for double byte characters
 - see IBM DOS Technical Reference Manual for more details

:int 21,44,d:ioctl,d
^INT 21,44,D / IOCTL,D - Generic I/O for Block Devices

 AH = 44h
 AL = 0D
 BL = drive number (0=default, 1=A:, 2=B:, 3=C:, ...)
 CH = device type
    = 08 for disk drive  (block device)
 CL = minor function code
    = 40  set device parameters
    = 41  write track on logical device
    = 42  format/verify track on logical drive
    = 47  set access flag  (DOS 4.x)
    = 60  get device parameters
    = 61  read track on logical device
    = 62  verify track on logical drive
    = 67  get access flag  (DOS 4.x)
 DS:DX = pointer to parameter block


 on return
 AX = error code if CF set  (see DOS ERROR CODES)


 - provides device independent primitive control operations
 - implemented from DOS 3.2
 - see IBM DOS Technical Reference Manual for more details

:int 21,44,e:ioctl,e
^INT 21,44,E / IOCTL,E - Get Logical Drive


 AH = 44h
 AL = 0E
 BL = physical drive number (0=default, 1=A:, 2=B:, 3=C:, ...)


 on return
 AX = error code if CF set  (see DOS ERROR CODES)
 AL = logical drive number assigned to physical drive
    = 0 if drive accessed by only one drive specifier
    = 1 if drive A:, 2 if drive B:, etc


 - used to determine the last drive designator used to access
   a drive if more than one logical drive designation applies
   to a device
 - implemented from DOS 3.2

:int 21,44,f:ioctl,f
^INT 21,44,F / IOCTL,F - Set Logical Drive


 AH = 44h
 AL = 0F
 BL = new drive number (0=default, 1=A:, 2=B:, 3=C:, ...)


 on return
 AX = error code if CF set  (see DOS ERROR CODES)
 AL = logical drive number (should be equal to BL input)
    = 0 if drive accessed by only one drive specifier
    = 1 if drive A:, 2 if drive B:, etc



 - changes the logical drive designator of the physical drive
   to be accessed next
 - implemented from DOS 3.2

:int 21,45
^INT 21,45 - Duplicate File Handle


 AH = 45h
 BX = file handle


 on return:
 AX = new file handle if CF not set
    = error code if CF set  (see DOS ERROR CODES)


 - gets another file handle for the same file
 - both file handles move in unison
 - often used to flush file data and update a file directory
   entry without closing the initial file

:int 21,46
^INT 21,46 - Force Duplicate File Handle


 AH = 46h
 BX = existing file handle
 CX = second file handle


 on return:
 AX = error code if CF set  (see DOS ERROR CODES)


 - if file handle in CX is currently open, current file
   identified by CX is closed and the handle in BX is
   dupped and placed in CX
 - after duping file handles move together through file
 - similar to INT 21,45

:int 21,47
^INT 21,47 - Get Current Directory


 AH = 47h
 DL = drive number (0 = default, 1 = A:)
 DS:SI = pointer to a 64 byte user buffer


 on return:
 DS:SI = pointer ASCIIZ directory path string
 AX = error code if CF set  (see DOS ERROR CODES)


 - returns the current directory relative to the root directory
 - the leading slash "\" and drive designator are omitted

:int 21,48
^INT 21,48 - Allocate Memory

 AH = 48h
 BX = number of memory paragraphs requested


 on return:
 AX = segment address of allocated memory block (MCB + 1para)
    = error code if CF set  (see DOS ERROR CODES)
 BX = size in paras of the largest block of memory available
      if CF set, and AX = 08 (Not Enough Mem)
 CF = 0 if successful
    = 1 if error


 - returns segment address of allocated memory block AX:0000
 - each allocation requires a 16 byte overhead for the MCB
 - returns maximum block size available if error

 - see   MCB
:int 21,49
^INT 21,49 - Free Allocated Memory


 AH = 49h
 ES = segment of the block to be returned (MCB + 1para)


 on return:
 AX = error code if CF set  (see DOS ERROR CODES)


 - releases memory and MCB allocated by INT 21,48
 - may cause unpredictable results is memory wasn't allocated
   using INT 21,48 or if memory not allocated to current process
 - checks for valid MCB id, but does NOT check for process ownership
 - care must be taken when freeing the memory of another process, to
   assure the segment isn't in use by a TSR or ISR

:int 21,4a
^INT 21,4A - Modify Allocated Memory Block  (SETBLOCK)


 AH = 4A
 BX = new requested block size in paragraphs
 ES = segment of the block (MCB + 1 para)


 on return:
 AX = error code if CF set  (see DOS ERROR CODES)
 BX = maximum block size possible, if CF set and AX = 8


 - modifies memory blocks allocated by  INT 21,48
 - can be used by programs to shrink or increase the size
   of allocated memory

:int 21,4b:exec function
^INT 21,4B - EXEC/Load and Execute Program

 AH = 4B
 AL = 00 to load and execute program
    = 01 (Undocumented)  create program segment prefix and load
         program, but don't execute.  The CS:IP and SS:SP of the
         program is placed in parameter block.  Used by debuggers
    = 03 load program only
 DS:DX = pointer to an ASCIIZ filename
 ES:BX = pointer to a parameter block


 on return:
 AX = error code if CF set  (see DOS ERROR CODES)
 ES:BX = pointer to parameter block similar to:

%Offset Size            Description

   00   word   segment of environment or zero if using parents env.
        word   segment of load point for overlay (if AL=3)
   02   dword  pointer to cmd line at PSP 80h
        word   relocation factor for EXE overlay (if AL=3)
   06   dword  pointer to default FCB passed at PSP 5Ch
   0A   dword  pointer to default FCB passes at PSP 6Ch
   0E   dword  value of program SS:SP
   12   dword  value of program CS:IP


 - allows execution of an external program as well as overlay
   management from within an application
 - all registers except CS and IP are destroyed
 - SS and SP should be preserved in code segment before call
   since a bug in DOS version 2.x destroys these
 - return code can be retrieved if child process exits via INT 21,4C
 - calling process must assure presence of enough unallocated memory
 - calls INT 21,55

 - see   PSP   UNDOC   INT 21,26   INT 21,55

:int 21,4c
^INT 21,4C - Terminate Process With Return Code


 AH = 4C
 AL = return code (for batch files)


 returns nothing


 - approved method of program termination
 - restores the terminate, ctl-break, and critical error exit
   addresses, flushes all buffers, frees memory and returns to
   DOS via the termination handler address
 - does not close FCBs
 - this function is not supported in versions of DOS before 2.x,
   so to exit use  INT 21,0  or  INT 20.


 - see   INT 20   INT 27   INT 21,0   INT 21,31

:int 21,4d
^INT 21,4D - Get Return Code of Sub-process


 AH = 4D


 on return:
 AH = system exit code  (indicates normal termination)
    = 00 for normal termination
    = 01 if terminated by ctl-break
    = 02 if critical device error
    = 03 if terminated by INT 21,31
 AL = child exit code


 - retrieve child process and system exit codes
 - this function can only be used to retrieve the exit code once
   multiple attempts to read exit codes will cause errors

:int 21,4e
^INT 21,4E - Find First Matching File

 AH = 4E
 CX = attribute used during search  (see FILE ATTRIBUTES)
 DS:DX = pointer to ASCIIZ filespec, including wildcards


 on return:
 AX = error code if CF set  (see DOS ERROR CODE)
 DTA = data returned from call in the format:

%Offset Size      Description

   00   byte    attribute of search (undocumented)
   01   byte    drive used in search  (undocumented)
   02  11bytes  search name used (undocumented)
   0D   word    directory entry number (0 based, DOS 3.x+, undoc.)
   0F   word    starting cluster number of current directory
                zero for root directory  (DOS 3.x+, undocumented)
   11   word    reserved (undocumented)
   13   word    starting cluster number of current directory
                zero for root directory  (DOS 2.x+, undocumented)
   15   byte    attribute of matching file
   16   word    file time  (see FILE ATTRIBUTES)
   18   word    file date  (see FILE ATTRIBUTES)
   1A   word    file size
   1E 13bytes   ASCIIZ filename and extension in the form NAME.EXT
                with blanks stripped

 - returns information on first file matching specifications
 - use INT 21,4F to retrieve following file matches
 - DOS 2.x cannot find . and .. entries, while DOS 3.x can
   unless they represent the root directory
 - normal files are always included along with files that match
   the requested attributes except when the LABEL attribute is
   requested.  It's up to the programmer to determine which
   actually match the requested attributes.
 - see   INT 21,1A   INT 21,4F   DTA   FILE ATTRIBUTES

:int 21,4f
^INT 21,4F - Find Next Matching File


 AH = 4F
 DS:DX = unchanged from previous function 4E


 on return:
 AX = error code if CF set  (see DOS ERROR CODES)


 - INT 21,4E should be called to find the first file and this
   function should be called to find all other matching files
 - normal files are always included along with files that match
   the requested attributes except when the LABEL attribute is
   requested.  It's up to the programmer to determine which
   actually match the requested attributes.
 - see   INT 21,4E   INT 21,1A   DTA   FILE ATTRIBUTES

:int 21,50
^INT 21,50 - Set Current Process ID  (Undocumented DOS 2.x)


 AH = 50h
 BX = process ID number (process PSP segment address)


 returns nothing


 - the process ID  number is actually the segment address
   of program's PSP.   This is useful for TSR's to access
   their own file handle table inside their PSP.

 - see   UNDOC   INT 21,51   INT 21,62

:int 21,51
^INT 21,51 - Get Current Process ID  (Undocumented DOS 2.x)

 AH = 51h

 on return:
 BX = process ID


 - The process ID  number is actually the segment address
   of program's PSP.   This in conjunction with INT 21,50
   is useful for TSR's to access their own file handle table
   in their respective PSP.
 - INT 21,62 is highly recommended for DOS 3.x due to a
   possible bug when activated from a TSR.  DOS may switch to
   the wrong internal stack which may cause a problems with
   TSR's if called during an INT 28.

 - see INT 21,62 (Get PSP segment) for DOS 3.x applications
 - see   UNDOC   INT 21,50

:int 21,52:invars
^INT 21,52 - Get Pointer to DOS "INVARS"  (Undocumented)

 AH = 52h

 on return:
 ES:BX = pointer to DOS "invars", a table of pointers used by DOS.
         Known "invars" fields follow (varies with DOS version):

%Offset Size              Description

  -12   word   sharing retry count (DOS 3.1+)
  -10   word   sharing retry delay  (DOS 3.1+)
   -8   dword  pointer to current disk buffer (DOS 3.x)
   -4   word   pointer in DOS code segment of unread CON input;
               0 indicates no unread input (DOS 3.x)
   -2   word   segment of first Memory Control Block
   00   dword  pointer to first DRIVE PARAMETER TABLE (A:) in chain
   04   dword  pointer to DOS System File Table (SFT)
   08   dword  pointer to $CLOCK device driver
   0C   dword  pointer to CON device driver
   10   byte   number of logical drives in system
   11   word   maximum bytes/block of any block device
   13   dword  pointer to DOS cache buffer header
   17 18bytes  NUL device header, first 4 bytes of device header
               point to the next device in device chain


^DOS 3.0 Specific Information

%Offset Size             Description

   10   byte   number of block devices
   11   word   max sector size used by DOS prior to loading block
               device drivers;  limits allowable device sector size
   13   dword  pointer to DOS cache buffer header
   17   dword  pointer to drive information table
   1B   byte   value of LASTDRIVE command in CONFIG.SYS
   1C   dword  pointer to STRING= workspace area
   20   word   size of STRING area (CONFIG.SYS value of STRING=x)
   22   dword  FCB file table pointer
   26   word   number of protected FCBs
   28  18bytes NUL device header, first 4 bytes of device header
               point to the next device in device chain


^DOS 3.1-3.3  Specific Information

%Offset Size              Description

   10   word   max sector size used by DOS prior to loading block
               device drivers;  limits allowable device sector size
   12   dword  pointer to DOS cache buffer header
   16   dword  pointer to drive information table
   1A   dword  FCB file table pointer
   1E   word   number of protected FCBs
   20   byte   number of block devices
   21   byte   value of LASTDRIVE command in CONFIG.SYS
   22  18bytes NUL device header, first 4 bytes of device header
               point to the next device in device chain
   34   byte   number of JOIN'ed drives


^DOS 4.x  Specific Information

%Offset Size             Description

   10   word   max sector size used by DOS prior to loading block
               device drivers;  limits allowable device sector size
   12   dword  pointer to DOS cache buffer header
   16   dword  pointer to drive information table
   1A   dword  FCB file table pointer
   1E   word   number of protected FCBs
   20   byte   number of block devices
   21   byte   value of LASTDRIVE command in CONFIG.SYS (default 5)
   22  18bytes NUL device header, first 4 bytes of device header
               point to the next device in device chain
   34   byte   ???
   35   word   pointer within IBMDOS code segment to list of special
               program names
   37   dword  ???
   3B   dword  pointer to chain of installable file system drivers
   3F   word   the x in BUFFERS x,y (rounded up to multiple of 30
               if EMS is used)
   41   word   the y in BUFFERS x,y
   43   byte   boot drive (1=A:)
   44   byte   ???
   45   byte   extended memory size in K bytes


 - see   UNDOC   INDOS   MCB   SFT   DPT   INT 21,5D


:int 21,53
^INT 21,53 - Generate Drive Parameter Table  (Undocumented)


 AH = 53h
 DS:SI = address of BIOS Parameter Block (BPB)
 ES:BP = pointer to first Drive Parameter Table in chain (DPT)


 returns nothing


 - available since DOS 2.0+
 - translates BPB DOS Disk Parameter Table
 - see   UNDOC   DPT   BPB   INT 21,32   INT  21,52

:int 21,54
^INT 21,54 - Get Verify Setting


 AH = 54h


 on return:
 AL = 00  verify off
    = 01  verify on


 - returns value of disk read after write verification flag

 - see   INT 21,2E

:int 21,55
^INT 21,55 - Create New PSP  (Undocumented)

 AH = 55h
 DX = New PSP segment address


 - the following should be observed when using this function

   o  Allocate memory for the PSP and program code  (INT 21,48)
   o  Duplicate the PSP   (INT 21,55)
   o  Load program code into allocated segment above the new PSP
   o  Save Current PSP
   o  Set PSP to the PSP just created  (INT 21,50)
   o  Jump to start of code if .COM otherwise handle relocation,
      setup stack and registers


 - similar to INT 21,26 except the PSP is setup by DOS
 - invoked by INT 21,4B

 - see   UNDOC   INT 21,4B   INT 21,26
:int 21,56
^INT 21,56 - Rename File


 AH = 56h
 DS:DX = pointer to old ASCIIZ path/filename
 ES:DI = pointer to new ASCIIZ path/filename


 on return:
 AX = error code if CF set  (see DOS ERROR CODES)


 - supports full pathnames and allows renaming files across
   directories and in DOS 3.x allows renaming subdirectories
 - does not support use of wildcards
 - unpredictable result may occur if an opened file is renamed
 -

:int 21,57
^INT 21,57 - Get/Set File Date and Time Using Handle

 AH = 57h
 AL = 00  get date and time
    = 01  set date and time
    = 02  ??? (DOS 4.0+)
    = 04  ??? (DOS 4.0+)
 BX = file handle
 CX = time to set (if setting)
 DX = date to set (if setting)


 on return:
 AX = error code if CF set  (see  DOS ERROR CODES)
 CX = file time (if reading, see below)
 DX = file date (if reading, see below)

%Time encoding:

 │F│E│D│C│B│A│9│8│7│6│5│4│3│2│1│0│  Time in CX
  │ │ │ │ │ │ │ │ │ │ │ └─┴─┴─┴─┴────  two second incr (0-29)
  │ │ │ │ │ └─┴─┴─┴─┴─┴─────────────  minutes 0-59)
  └─┴─┴─┴─┴────────────────────────  hours (0-29)

%Date Encoding

 │F│E│D│C│B│A│9│8│7│6│5│4│3│2│1│0│  Date in DX
  │ │ │ │ │ │ │ │ │ │ │ └─┴─┴─┴─┴────  day (1-31)
  │ │ │ │ │ │ │ └─┴─┴─┴─────────────  month (1-12)
  └─┴─┴─┴─┴─┴─┴────────────────────  year - 1980
:int 21,58
^INT 21,58 - Get/Set Memory Allocation Strategy
^(Undocumented, DOS 3.x)

 AH = 58h
 AL = 00  get strategy code
    = 01  set strategy code
 BX = strategy code (when AL = 01)
    = 00  first fit  (default)
    = 01  best fit
    = 02  last fit

 on return:
 AX = strategy code if CF clear
    = error if CF set

 - defaults to first fit, first block large enough is chosen
 - in first fit, DOS searches the MCB chain from low addresses to
   high for the first block large enough to fill the request.  For
   best fit, DOS searches all memory blocks for the closest fit.
   In last fit, DOS starts at high addresses and works downward

 - see   DOS ERROR CODES   UNDOC
:int 21,59
^INT 21,59 - Get Extended Error Information (DOS 3.0+)

 AH = 59h
 BX = 00 for versions  3.0, 3.1, 3.2


 on return:
 AX = extended error code (see DOS ERROR CODES)
    = 0 if no error
 BH = error class
 BL = suggested action
 CH = locus


 - may be called after any  INT 21  function or from
   INT 24 when an error is returned
 - must be called immediately after the error occurs
 - registers CX, DX, DI, SI, BP, DS and ES are destroyed

 - see  DOS ERROR CODES
:int 21,5a
^INT 21,5A - Create Temporary File  (DOS 3.0+)


 AH = 5A
 CX = attribute
 DS:DX = pointer to ASCIIZ path ending in '\'


 on return:
 AX = handle if call CF clear
    = error code if CF set  (see DOS ERROR CODES)
 DS:DX = pointer to updated ASCIIZ filespec


 - creates files with random names with any combination of
   the following attributes: normal, system and hidden
 - ending backslash is required

:int 21,5b
^INT 21,5B - Create File  (DOS 3.0+)


 AH = 5B
 CX = attribute
 DS:DX = pointer to ASCIIZ path/filename


 on return:
 AX = handle if CF not set
    = error code if CF set  (see DOS ERROR CODES)


 - standard method of opening files
 - returns a file handle of a file opened with specified
   attributes (combinations of normal, system and hidden)

:int 21,5c
^INT 21,5C - Lock/Unlock File Access  (DOS 3.0+)

 AH = 5C
 AL = 00  lock file
    = 01  unlock file
 BX = file handle
 CX = most significant word of region offset
 DX = least significant word of region offset
 SI = most significant word of region length
 DI = least significant word of region length


 on return:
 AX = error code if CF set  (see DOS ERROR CODES)


 - used for networking and multi-tasking system to preserve
   data integrity
 - duplicated handles inherit access to locked regions
 - EXEC'd programs do not inherit access to locked regions
:int 21,5d
^INT 21,5D - Critical Error Information  (Undocumented, DOS 3.1+)

 AH = 5D
 AL = 00  copy data to DOS save area
    = 06  get address of critical flag into DS:SI
    = 0A  set extended error information
 DS:SI = pointer to 18 byte data block to be copied (AL = 00)
       = pointer to 9 byte data block of the form (AL = 0A):

%      Offset Size       Description

         00   word   extended error code to set
         02   dword  pointer to driver address to set
         06   byte   action code to set
         07   byte   class code to set
         08   byte   locus code to set

 on return:
 DS:SI = (AL = 6)address of critical flag of the form:

%      Offset Size      Description

         00   word   extended error code
         02   byte   action code
         03   byte   class code
         04   byte   pointer to driver address

 - function 0 copies 18 bytes from DS:SI to the DOS internal
   register-save area;  this data will be placed in the registers
   when DOS returns to the caller thereby circumventing the DOS
   register save logic
 - may be used by a TSR to prevent accidental changing of an error
   code and causing problems in the foreground process

 - see   INT 21,59   UNDOC

:int 21,5e
^INT 21,5E  AL=0  Get Machine Name  (DOS 3.1+)

 AH = 5E
 AL = 00 get machine name (see AL=02 and AL=03)
 DS:DX = far pointer to buffer receiving name string


 on return:
 AX = error code if CF set, (invalid function)
 CH = 0  if name not defined
    > 0  if name defined
 CL = NETBIOS name number, if CH not 0
 DS:DX = far pointer to buffer containing string if CH not 0


 - returns pointer to an ASCIIZ string identifying the
   computer on a Microsoft network
 - output string is a 15 bytes long, padded with blanks and
   null terminated
 - unpredictable if called without file sharing loaded


^INT 21,5E  AL=2  Set Printer Setup  (DOS 3.1+)


 AH = 5E
 AL = 02 set printer setup (see AL=0 and AL=3)
 BX = redirection list index (see INT 21,5F AL=2)
 CX = length of setup string
 DS:SI = far pointer to printer setup string


 on return:
 AX = error code if CF set, (invalid function)


 - see INT 21,5F subfunction 2 for information on obtaining
   the redirection list index
 - fails if file sharing is not loaded


^INT 21,5E  AL=3  Get Printer Setup  (DOS 3.1+)


 AH = 5E
 AL = 03 get printer setup (see AL=0 and AL=2)
 BX = redirection list index (see INT 21,5F AL=2)
 ES:DI = far pointer to buffer to receive setup string


 on return:
 AX = error code if CF set, (invalid function)


 - see INT 21,5F subfunction 2 for information on obtaining
   the redirection list index
 - fails if file sharing is not loaded


:int 21,5f
^INT 21,5F  AL=2  Get Redirection List Entry  (DOS 3.1+)

 AH = 5F
 AL = 02
 BX = redirection list index
 DS:SI = far pointer to a 16 byte buffer to hold device name
 ES:DI = far pointer to a 128 byte buffer to hold network name

 on return:
 AX = error code if CF is set
    = 1  invalid function code
    = 12 no more files
 BH = device status flag,
    bit 0 = 0  device valid
    bit 0 = 1  device invalid
 BL = device type
    = 3  printer
    = 4  drive
 CX = stored parameter value
 DS:SI = far pointer to ASCIIZ local device name
 ES:DI = far pointer to ASCIIZ network name

 - value returned in CX is the value previously passed to
   INT 21,5F with subfunction 3 in register CX
 - registers DX and BP are destroyed
 - fails if file sharing is not loaded


^INT 21,5F  AL=3  Redirect Device  (DOS 3.1+)

 AH = 5F
 AL = 3
 BL = device type
    = 3 if printer
    = 4 if drive
 CX = parameter to save for caller
 DS:SI = far pointer to ASCIIZ local device name
 ES:DI = far pointer to ASCIIZ network name followed
         by ASCIIZ password

 on return
 AX = error code if CF is set
    = 1  invalid function code or
         invalid source or destination string format or
         source device already redirected
    = 3  path not found
    = 5  access denied
    = 8  insufficient memory

 - parameter passed in CX can later be retrieved by calls
   to INT 21,5F subfunction 2
 - local device name in DS:SI can be a drive designator
   (D:), a printer name (PRN or LPTx), or a null string
 - when a null string is followed by a password is used, DOS
   tries granting access to the network directory using the
   given password
 - fails if file sharing is not loaded


^INT 21,5F  AL=4  Cancel Device Redirection  (DOS 3.1+)

 AH = 5F
 AL = 04
 DS:SI = far pointer to ASCIIZ local device name


 on return
 AX = error code if CF set
    = 01  function code invalid
          ASCIIZ string is not an existing source device
    = 0F  redirection paused on server


 - local device name in DS:SI can be a drive designator
   (D:), a printer name (PRN or LPTx), or a string beginning
   with 2 backslashes "\\"
 - when two backslashes are used for the string the connection
   between the local machine and network directory terminates
 - fails if file sharing is not loaded

:int 21,60
^INT 21,60 - Get Fully Qualified File Name (Undocumented 3.x+)


 AH = 60h
 DS:SI = address of an ASCIIZ string containing unqualified filename
 ES:DI = address of a buffer to contain fully qualified filename


 on return:
 ES:DI = address of fully qualified filename string


 - undocumented, available in DOS 3.x+
 - does not check for file existence, simple provides a fully
   qualified filename for the given filespec.
 - see   UNDOC

:int 21,62
^INT 21,62 - Get PSP address  (DOS 3.x)


 AH = 62h


 on return:
 BX = segment address of current process



 - this is useful for TSR's to access their own file handles
 - for DOS 2.x use INT 21,51


 - see   INT 21,51   INT 21,50

:int 21,63
^INT 21,63 - Get Lead Byte Table  (MSDOS 2.25 only)


 AH = 63h
 AL = 00  get address of system lead byte table
    = 01  set or clear interim console flag
    = 02  get value of interim console flag
 DL = 00  if AL=01, clear interim console flag
    = 01  if AL=01, set interim console flag


 on return
 DL = value of interim console flag, function 02
 DS:SI = far pointer to lead byte table, function 00


 - available only in MSDOS 2.25
 - function 00, returns the address of system table containing
   legal lead byte ranges
 - function 01 and 02 set and get the interim console flag

:int 21,64
^INT 21,64 - Set Device Driver Look Ahead  (Undocumented)


 AH = 64h
 AL = value for switch
      00 - causes DOS to perform look ahead to the device driver
           before execution of INT 21 functions 01, 08, and 0A
      other - no look ahead is performed


 returns ???


 - DOS internal; should not be called by user program
 - switch defaults to zero
 - undocumented; since DOS 3.3
 - see   UNDOC


:int 21,65
^INT 21,65 - Get Extended Country Information (DOS 3.3+)


 AH = 65h
 AL = 01  get extended country information
    = 02  get pointer to character translation table
    = 04  get pointer to filename character translation table
    = 05  reserved
    = 06  Get pointer to collating sequence
    = 07  Get segment of DCBS vector (DOS 4.x)
 BX = code page (-1 = current)
 CX = amount of data to return
 DX = country ID (-1 = current)
 ES:DI = pointer to output buffer


 on return
 AX = error code if CF is set  (see DOS ERROR CODES)
 CX = amount of data returned
 ES:DI pointer to returned table


%Offset Size     Table for Function 01

   00   byte   country id = 01
   01   word   size (38 or less)
   03   word   country id
   05   word   code Page
   07   word   date Format
   09  5bytes  currency symbol string (ASCIIZ)
   0E  2bytes  thousands separator string (ASCIIZ)
   10  2bytes  decimal separator string (ASCIIZ)
   12  2bytes  date separator string (ASCIIZ)
   14  2bytes  time Separator string (ASCIIZ)
   16   byte   currency symbol location
   17   byte   currency decimal places
   18   byte   time format
   19   dword  extended ASCII map call address
   1D  2bytes  list separator string (ASCIIZ)
   1F  10bytes reserved


%Offset Size     Table for Function 2
   00   byte   country Id = 02
   01   dword  pointer to uppercase table


%Offset Size     Table for Function 4
   00   byte   country Id = 04
   01   dword  pointer to filename uppercase table


%Offset Size     Table for Function 6
   00   byte   country Id = 06
   01   dword  pointer to collating table


%Offset Size     Table for Function 7
   00   byte   country Id = 07
   01   dword  pointer to byte pair table


:int 21,66
^INT 21,66 - Get/Set Global Code Page  (DOS 3.3+)


 AH = 66h
 AL = 01  get global code page
    = 02  set global code page
 BX = active code page if setting
 DX = system code page if setting


 on return
 AX = error code if CF set  (see DOS ERROR CODES)
 BX = active code page  (for AL=1 only)
 DX = system code page  (for AL=1 only)


 - moves country data from COUNTRY.SYS to country memory table

:int 21,67
^INT 21,67 - Set Handle Count  (DOS 3.3+)

 AH = 67h
 BX = new maximum open handles allowed

 on return
 CF = 0 if successful
    = 1 if error
 AX = error code if CF is set  (see DOS ERROR CODES)


 - gives program control of the number of files simultaneously open
 - if CX is less than the current number of open files the change
   will take effect when the number of open handles falls below
   the new limit
 - this function allows the application to use more than 20 files,
   up to the FILES=N limit
 - earlier copies of IBM DOS 3.3 sometimes incorrectly allocates
   memory if an even number of handles is requested

 - see   SFT   FILE HANDLES
:int 21,68
^INT 21,68 - Flush Buffer Using Handle  (DOS 3.3+)


 AH = 68h
 BX = file handle


 on return
 AX = error code if CF set  (see DOS ERROR CODES)


 - flushes DOS buffers to disk, does not update directory entry

:int 21,69
^INT 21,69 - Get/Set Disk Serial Number  (Undocumented DOS 4+)

 AH = 69h
 AL = 00 get serial number
    = 01 set serial number
 BL = drive (0 = default, 1=A:, 2 = B:, ... )
 DS:DX = buffer to contain extended BIOS Parameter Block (AL=0)
       = disk information to set of the form:

%     Offset Size       Description
        00   word    info level (zero)
        02   dword   disk serial number (binary)
        06  11bytes  volume label or "NO NAME    " if not present
        11   8bytes  filesystem type string "FAT12   " or "FAT16   "

 returns:
 AX = error code if CF set; value destroyed otherwise
      1 - network drive not supported
      5 - non extended BPB on disk
 DS:DX = pointer to returned data, when AL = 0
 CF = 0 if successful
    = 1 if error


 - copies data from Extended BIOS Parameter Block to buffer
 - no critical error is generated on error
 - does not work on network drives

 - see   UNDOC   INT 21,59   BPB
:int 21,6c
^INT 21,6C - Extended Open/Create  (DOS 4.x+)

 AH = 6C
 AL = 00
 BX = open mode (see below)
 CX = file attribute (see FILE ATTRIBUTES, bits 15-8 are zero)
 DX = function control indicator (see below)
 DS:SI = ASCIIZ filespec


 returns:
 AX = handle if CF clear
    = error code if CF set  (see DOS ERROR CODES)
 CX = 01  file opened
    = 02  file created and opened
    = 03  file truncated and opened (replaced)
 CF = 0 if successful
    = 1 if error


%Open Mode in BX:

 │F│E│D│C│B│A│9│8│7│6│5│4│3│2│1│0│  BX  (Open Mode)
  │ │ │ │ │ │ │ │ │ │ │ │ │ └─┴─┴──── read/write access mode
  │ │ │ │ │ │ │ │ │ │ │ │ └──────── reserve (must be 0)
  │ │ │ │ │ │ │ │ │ └─┴─┴──────── sharing mode
  │ │ │ │ │ │ │ │ └──────────── 1 = private, 0 = inheritable
  │ │ │ └─┴─┴─┴─┴──────────── reserved
  │ │ └──────────────────── 0 = call INT 24, 1 = ignore INT 24
  │ └──────────────────── 0 = normal write, 1 = flush each write
  └──────────────────── reserved

%Read/Write Access bits:     Sharing Mode bits:
%210                           654
 000  read access              000  compatibility mode
 001  write access             001  read/write access
 010  read/write access        010  write access denied
                               011  read access denied
                               100  full access

%Function Control Indicator in DX:

 │F│E│D│C│B│A│9│8│7│6│5│4│3│2│1│0│  DX  (Function Control)
  │ │ │ │ │ │ │ │ │ │ │ │ └─┴─┴─┴──── file existence behavior
  │ │ │ │ │ │ │ │ └─┴─┴─┴─────────── creation behavior
  └─┴─┴─┴─┴─┴─┴─┴────────────────── reserved

%File Existence Behavior bits:
%3210
 0000  if file exist, generate error, take no action
 0001  if file exists, open file
 0010  if file exists, truncate and open


%Creation Behavior bits:
%7654
 0000  if file does not exist, generate error, take no action
 0001  if file does not exist, create


:int 21,f8
^INT 21,F8 - Set OEM Int 21 Handler (functions F9-FF, Undocumented)


 AH = F8
 DS:DX = pointer to OEM handler for INT 21H calls F9 through FF
       = FFFF:FFFF to reset to original handlers


 - DOS is set up to allow ONE handler for all 7 function calls.
   Any call to these handlers will set the CF and AX
   will contain 1 if they are not initialized.   The handling
   routine is passed all registers just as the user set them.
   The handler should exit with an IRET.
 - see   UNDOC

:int 22
^INT 22 - Program Terminate


 no input data


 - not an interrupt, but a vector to the terminate address
 - copied to PSP offset 0Ah during program load
 - do not execute this interrupt directly


 - see   PSP

:int 23:ctrl-c
^INT 23 - Control-Break Exit Address

 no input data

 - not an interrupt but a pointer to a routine that is called when a
   DOS function detects a Ctrl-Break or Ctrl-C has been pressed
   resulting in a "Break condition"
 - a Break condition is detected if DOS's internal Break flag is
   found set by INT 1B or the next word in the BIOS keyboard buffer
   is a scan code representing one of the Break key combinations.
   If a matching scan code is found, the keyboard buffer head pointer
   is incremented by 2 (which effectively removes the ^C keycode), the
   ^C is printed and then INT 23 is called.
 - disabling the abort is easy, but to disable the ^C from appearing
   you must either not use any of the DOS I/O functions that check
   for Break or you must trap the Ctrl-C keypress from within INT 9.
   Another method is to scan the BIOS keyboard buffer and delete any
   Break key combinations.
 - Ctrl-Break empties the keyboard buffer by resetting the keyboard
   head and tail pointers then places a 0000h at the queue head.  It
   then sets an internal "Break" flag.  DOS subfunctions that check
   for Break see this and then issue INT 23h.  DOS does not detect
   INT 1B using the keyboard buffer, but uses it's own internal flag.
 - Alt-Keypad-3 and Ctrl-2 also result in this interrupt
 - Ctrl-C places 2E03h in the BIOS keyboard buffer while Ctrl-2
   places 0300h and Alt-Keypad-3 places 0003h;  none of these key
   combinations empty the keyboard like Ctrl-Break but all result
   in a ^C being displayed;  note that all three produce scan codes
   containing '03'
 - since DOS checks only the first word of the keyboard buffer
   Ctrl-C, Ctrl-2 and Alt-Keypad-3 are only detected if they are the
   first word in the buffer while Ctrl-Break is detected via the
   internal flag and takes effect as soon as it's detected.
 - do not execute this interrupt directly

 - see   INT 1B    PSP   CTRL-BREAK   INT 9    HOW-DO-I

:int 24:critical error handler
^INT 24 - Critical Error Handler

 no input data

 on entry to INT 24:
 AH = bit 7 of register AH is set to one if other than disk error
    = bit 7 of register AH is set to zero if disk error
      AL = failing drive number
      AH = bits 0-2 indicate affected disk area and read/write status

           │5│4│3│2│1│0│  AH
            │ │ │ │ │ └──── read = 0, write = 1
            │ │ │ └─┴───── 00=DOS, 01=FAT, 10=DIR, 11=data area
            │ │ └──────── 0=FAIL not allowed, 1=FAIL allowed
            │ └───────── 0=RETRY not allowed, 1=RETRY allowed
            └────────── 0=IGNORE not allowed, 1=IGNORE allowed

 DI = error code in lower byte
 BP:SI = pointer to device header control block where additional
         information about the error can be found


 on exit:
 AL = action code determining exit behavior
    = 00  ignore error
    = 01  retry
    = 02  terminate through INT 23
    = 03  fail system call (DOS 3.x+)


%Error Codes in low order byte of DI:

   00  write protect error
   01  unknown unit
   02  drive not ready
   03  unknown command
   04  data error (bad CRC)
   05  bad request structure length
   06  seek error
   07  unknown media type
   08  sector not found
   09  printer out of paper
   0A  write fault
   0B  read fault
   0C  general failure

%Users Stack at Entry to Error Handler:

 (top of stack)
     IP         DOS code next instruction pointer
     CS
     FLAGS      DOS's flags
     AX -\
     BX   \
     CX    \
     DX     \
     SI      |- User's registers at entry to INT 21 function
     DI     /
     BP    /
     DS   /
     ES -/
     IP         User code next instruction pointer
     CS
     FLAGS

 - on entry registers are setup for a retry operation
 - user routine must issue an IRET or simulate an IRET
 - INT 21,00 through INT 21,0C and INT 21,59 can safely be invoked
   from the handler.  Other calls may destroy DOS's stack
 - handler must preserve register SS,SP,DS,ES,BX,CX,DX
 - choosing ignore can show side effects, since it causes DOS
   to continue as if it the call were successful
 - if an improper action code is specified in DOS 3.x it is changed:
   if IGNORE is invalidly specified, action is converted to FAIL
   if RETRY is invalidly specified, action is converted to FAIL
   if FAIL is invalidly specified, action is converted to ABORT
 - IGNORE requests are converted to FAIL for FAT and DIR disk errors
   and network crritical errors
 - if the user routine wishes to handle the error instead of passing it
   to DOS, it must restore the user program registers from the stack
   and remove all the last 3 words from the stack (FLAGS, CS, IP)
   ad issue an IRET
   remove all registers from the stack
 - do not execute this interrupt directly
 - INDOS flag is cleared on INT 24 (see INT 21,34)


:int 25
^INT 25 - Absolute Disk Read

 AL = logical drive number (0=A:, 1=B:, 2=C:, ...)
 CX = number of sectors to read
    = -1 if DOS 4.x (control block pointer is in DS:BX)
 DX = starting logical sector number (see below for DOS 4.x+)
 DS:BX = pointer to data buffer
       = pointer to control block (DOS 4.x+, see below)

 on return:
 AH = error code if CF set:
      01  bad command
      02  bad address mark
      03  write protect
      04  sector not found
      08  DMA failure
      10  data error (bad CRC)
      20  controller failed
      40  seek failed
      80  attachment failed to respond
 AL = BIOS error code if CF set
      00  write protect error
      01  unknown unit
      02  drive not ready
      03  unknown command
      04  data error (bad CRC)
      05  bad request structure length
      06  seek error
      07  unknown media type
      08  sector not found
      0A  write fault
      0B  read fault
      0C  general failure

^Control Block Format (DOS 4.x):

%Offset Size        Description

   00   dword  starting sector
   04   word   number of sectors to read
   06   dword  pointer to buffer


 - reads disk sectors into buffer at DS:BX or DS:[BX+6]
 - after calling this interrupt the flags register remains on the
   stack and must be popped manually
 - sectors are logical sectors starting at the beginning of a
   logical disk; each DOS partition on a drive unit is considered
   one logical drive and has it's own logical sector numbers with
   track 0 starting at the first track in the partition
 - this function uses logical drives, and is susceptible to ASSIGN
 - physical sector numbers can be converted to and from DOS sector
   numbers with the following formulas:

   dos_sector = (sector - 1) + (head * sectors_per_track) +
                (track * sectors_per_track * num_heads)

   physical_sector = 1 + (dos_sector  MOD  sectors_per_track)
   physical_head = (dos_sector / sectors_per_track)  MOD  num_heads
   physical_track = dos_sector / (sectors_per_track * num_heads)

 - see   INT 13,STATUS

:int 26
^INT 26 - Absolute Disk Write

 AL = logical drive number (0=A:, 1=B:, 2=C:, ...)
 CX = number of sectors to write
    = -1 if DOS 4.x (control block pointer is in DS:BX)
 DX = starting logical sector number (see below for DOS 4.x+)
 DS:BX = pointer to data buffer
       = pointer to control block (DOS 4.x+, see below)

 on return:
 AH = error code if CF set:
      01  bad command
      02  bad address mark
      03  write protect
      04  sector not found
      08  DMA failure
      10  data error (bad CRC)
      20  controller failed
      40  seek failed
      80  attachment failed to respond
 AL = BIOS error code if CF set
      00  write protect error
      01  unknown unit
      02  drive not ready
      03  unknown command
      04  data error (bad CRC)
      05  bad request structure length
      06  seek error
      07  unknown media type
      08  sector not found
      0A  write fault
      0B  read fault
      0C  general failure

^Control Block Format (DOS 4.x):

%Offset Size      Description

   00   dword  starting sector
   04   word   number of sectors to write
   06   dword  pointer to buffer


 - writes disk sectors from buffer at DS:BX or DS:[BX+6]
 - after calling this interrupt the flags register remains on the
   stack and must be popped manually
 - sectors are logical sectors starting at the beginning of a
   logical disk; each DOS partition on a drive unit is considered
   one logical drive and has it's own logical sector numbers with
   track 0 starting at the first track in the partition
 - this function uses logical drives, and is susceptible to ASSIGN
 - physical sector numbers can be converted to and from DOS sector
   numbers with the following formulas:

   dos_sector = (sector - 1) + (head * sectors_per_track) +
                (track * sectors_per_track * num_heads)

   physical_sector = 1 + (dos_sector  MOD  sectors_per_track)
   physical_head = (dos_sector / sectors_per_track)  MOD  num_heads
   physical_track = dos_sector / (sectors_per_track * num_heads)

 - see   INT 13,STATUS
:int 27
^INT 27 - Terminate and Stay Resident


 DX = offset of last byte in program to remain resident plus 1
 CS = segment of PSP


 returns nothing


 - terminates process without closing open files
 - memory beyond the offset in DX is freed


 - see   INT 21,31

:int 28:dos scheduler
^INT 28 - DOS Idle Loop / Scheduler  (Undocumented)




 - issued by DOS during keyboard poll loop
 - indicates DOS may be carefully re-entered by TSR
 - used by TSR programs to popup and make DOS disk I/O calls
 - see   INDOS   UNDOC

:int 29
^INT 29 - DOS Fast Character I/O  (Undocumented)


 AL = character to write


 returns nothing ???


 - used by DOS device drivers
 - similar to (int 21,2) and (int 21,9) but much faster
 - advances the cursor after character output
 - see   UNDOC

:int 2a
^INT 2A - DOS Critical Section and NETBIOS

%Functions requested in AH; see also  INT 2A,N  where N is:

  00  Network presence test
  03  Network direct I/O test
  04  NETBIOS execute
  05  Get network information


 - subfunctions aren't currently listed in HelpPC but will be added
   shortly
:int 2e
^INT 2E - Execute Command Using Base Level Command Interpreter
^(Undocumented)

 DS:SI = ASCIIZ command string to be executed


 returns nothing ???

 - first byte of the string contains the string length, inclusive
 - command string should end with a CR
 - SS & SP should be preserved in your own code segment
 - available since DOS 2.x
 - can be used to modify parents environment with SET command
 - incompatible under some software multitasking systems
 - before returning to the parent program this interrupt will
   attempt to execute the "current" batch file (if the parent or
   any ancestors were invoked from a batch file.   This can cause
   remaining lines in a batch file to execute before the parent
   program finishes and fragment memory.

 - see   UNDOC
:int 2f:multiplex interrupt
^INT 2F - DOS Multiplex Interrupt

%Function requested in AL; see also  INT 2F,N  where N is:

    0  Get installed state         │ ---- ERROR CODES ----
    1  Submit file                 │ 01  Invalid function
    2  Cancel file                 │ 02  File not found
    3  Cancel all files            │ 03  Path not found
    4  Pause / return status       │ 04  Too many files
    5  End of status               │ 05  Access denied
   2E  Error Translation Tables    │ 08  Queue full
                                   │ 09  Busy
                                   │ 0C  Name too long
                                   │ 0F  Invalid drive


 - see   INT 2F,0  for installation checks

:int 2f,0
^INT 2F,0 - DOS Multiplex Interrupt - Get Installed State

 AL = 00
 AH = 01  PRINT
      02  ASSIGN
      10  SHARE
      11  Redirector/IFS is resident
      12  MultiDOS is resident
      13  Swap 13h and 19h
      14  NLSFUNC
      15  CD-ROM
      16  Windows 386
      17  DOS shell
      19  DOS 4.0 SHELLB.COM
      1A  ANSI.SYS (DOS 4.0+)
      1B  XMA2EMS.SYS
      40  OS/2 Compatibility box
      43  Himem XMS driver
      7A  Novell Netware IPX
      AD  DISPLAY.SYS internal (DOS 3.3+)
      AE  DOS 3.3+ internal
      B0  GRAFTABL.COM (DOS 3.3+)
      B4  IBM 3270 emulation
      B7  APPEND  (DOS 3.3+)
      B8  PCLAN network
      B9  PCLAN RECEIVER.COM
      BF  PCLAN REDIRIFS.EXE
      C0-FF reserved for user applications


 on return:
 AL = 00  not installed, ok to install
    = 01  not installed, do not install
    = FF  installed


 - the installed test for append returns non-zero if installed;
   zero if not installed


:int 2f,1:dos multiplex
^INT 2F,1 - Multiplex Interrupt - Submit file


 AL = 01
 AH = 01  resident portion of PRINT
      02  resident portion of ASSIGN
      10  resident portion of SHARE
      B7  resident portion of APPEND
      C0-FF reserved for user applications
 DS:DX = pointer to a 5 byte packet containing an priority byte
         and a DWORD pointer to an ASCIIZ filename

 returns nothing



:int 2f,2
^INT 2F,2 - Multiplex Interrupt - Cancel file


 AL = 02
 AH = 01  resident portion of PRINT
      02  resident portion of ASSIGN
      10  resident portion of SHARE
      B7  resident portion of APPEND
      C0-FF reserved for user applications
 DS:DX = pointer to ASCIIZ filename to cancel


 returns nothing


 - accepts wildcards

:int 2f,3
^INT 2F,3 - Multiplex Interrupt - Cancel all files


 AL = 03
 AH = 01  resident portion of PRINT
      02  resident portion of ASSIGN
      10  resident portion of SHARE
      B7  resident portion of APPEND
      C0-FF reserved for user applications


 returns nothing

:int 2f,4
^INT 2F,4 - Multiplex Interrupt - Pause / return status


 AL = 04
 AH = 01  resident portion of PRINT
      02  resident portion of ASSIGN
      10  resident portion of SHARE
      B7  resident portion of APPEND
      C0-FF reserved for user applications


 on return:
 DX = error count
 DS:SI = pointer to queue of files


 - each file in the queue is represented by 64 byte filename
 - the file currently being printed is the first entry in the queue
 - the last entry in the queue is a null string

:int 2f,5
^INT 2F,5 - Multiplex Interrupt - End of Status


 AL = 05
 AH = 01  resident portion of PRINT
      02  resident portion of ASSIGN
      10  resident portion of SHARE
      B7  resident portion of APPEND
      C0-FF reserved for user applications


 on return:
 AH = error code  (see INT 2F)

:int 2f,2e
^INT 2F,2E - Setup Error Code Translation Tables  (undoc. DOS 4.x+)


 - discovered in DOS 4.x by Jim Kyle, this function provides more
   detailed information on the pending critical error.

:int 33:mouse interrupt:mouse services
^INT 33 - Mouse Function Calls

%Function request in AX;  see also  INT 33,N  where N is:

  00  Mouse Reset/Get Mouse Installed Flag
  01  Show Mouse Cursor
  02  Hide Mouse Cursor
  03  Get Mouse Position and Button Status
  04  Set Mouse Cursor Position
  05  Get Mouse Button Press Information
  06  Get Mouse Button Release Information
  07  Set Mouse Horizontal Min/Max Position
  08  Set Mouse Vertical Min/Max Position
  09  Set Mouse Graphics Cursor
  0A  Set Mouse Text Cursor
  0B  Read Mouse Motion Counters
  0C  Set Mouse User Defined Subroutine and Input Mask
  0D  Mouse Light Pen Emulation On
  0E  Mouse Light Pen Emulation Off
  0F  Set Mouse Mickey Pixel Ratio
  10  Mouse Conditional OFF
  13  Set Mouse Double Speed Threshold
  14  Swap interrupt subroutines
  15  Get mouse driver state and memory requirements
  16  Save mouse driver state
  17  Restore mouse driver state
  18  Set alternate subroutine call mask and address
  19  Get user alternate interrupt address
  1A  Set mouse sensitivity
  1B  Get mouse sensitivity
  1C  Set mouse interrupt rate (InPort only)
  1D  Set mouse CRT page
  1E  Get mouse CRT page
  1F  Disable mouse driver
  20  Enable mouse driver
  21  Reset mouse software
  22  Set language for messages
  23  Get language number
  24  Get driver version, mouse type & IRQ number


 - a mickey is 1/200 inches
 - for additional information see your vendor documentation
 - function number occupies all of AX rather than AH


^Mouse functions can be broken down into the following classes:

%Mouse Driver Control / Feedback Functions
  00  Mouse Reset/Get Mouse Installed Flag
  15  Get Mouse Driver State and Memory Requirements
  16  Save Mouse Driver State
  17  Restore Mouse Driver State
  1C  Set Mouse Interrupt Rate (InPort only)
  1F  Disable Mouse Driver
  20  Enable Mouse Driver
  21  Reset Mouse Software
  24  Get Driver Version, Mouse Type & IRQ Number

%Mouse Cursor Control Functions
  01  Show Mouse Cursor
  02  Hide Mouse Cursor
  04  Set Mouse Cursor Position
  07  Set Mouse Horizontal Min/Max Position
  08  Set Mouse Vertical Min/Max Position
  09  Set Mouse Graphics Cursor
  0A  Set Mouse Text Cursor
  0F  Set Mouse Mickey Pixel Ratio
  10  Mouse Conditional OFF
  13  Set Mouse Double Speed Threshold
  1A  Set Mouse Sensitivity
  1B  Get Mouse Sensitivity

%Mouse Button and Position Feedback Functions
  03  Get Mouse Position and Button Status
  05  Get Mouse Button Press Information
  06  Get Mouse Button Release Information
  0B  Read Mouse Motion Counters

%Video Control and Feedback Functions
  1D  Set Mouse CRT Page
  1E  Get Mouse CRT Page

%Mouse Interrupt Setup Functions
  0C  Set Mouse User Defined Subroutine and Input Mask
  14  Swap Interrupt Subroutines

%Alternate Mouse Interrupt Setup Functions
  18  Set Alternate Subroutine Call Mask and Address
  19  Get User Alternate Interrupt Address

%Light Pen Emulation Functions
  0D  Mouse Light Pen Emulation On
  0E  Mouse Light Pen Emulation Off

%International Language Support Functions
  22  Set Language for Messages
  23  Get Language Number

:int 33,0
^INT 33,0 - Mouse Reset/Get Mouse Installed Flag

 AX = 00


 on return:
 AX = 0000  mouse driver not installed
      FFFF  mouse driver installed
 BX = number of buttons


 - resets mouse to default driver values:

   .  mouse is positioned to screen center
   .  mouse cursor is reset and hidden
   .  no interrupts are enabled (mask = 0)
   .  double speed threshold set to 64 mickeys per second
   .  horizontal mickey to pixel ratio (8 to 8)
   .  vertical mickey to pixel ratio (16 to 8)
   .  max width and height are set to maximum for video mode
:int 33,1
^INT 33,1 - Show Mouse Cursor


 AX = 01


 returns nothing


 - increments the cursor flag;  the cursor is displayed if flag
   is zero;  default flag value is -1

:int 33,2
^INT 33,2 - Hide Mouse Cursor


 AX = 02


 returns nothing


 - decrements cursor flag; hides cursor if flag is not zero

:int 33,3
^INT 33,3 - Get Mouse Position and Button Status


 AX = 03


 on return:
 CX = horizontal (X) position  (0..639)
 DX = vertical (Y) position  (0..199)
 BX = button status:

    │F-8│7│6│5│4│3│2│1│0│  Button Status
      │  │ │ │ │ │ │ │ └──── left button (1 = pressed)
      │  │ │ │ │ │ │ └───── right button (1 = pressed)
      └──┴─┴─┴─┴─┴─┴────── unused


 - values returned in CX, DX are the same regardless of video mode

:int 33,4
^INT 33,4 - Set Mouse Cursor Position


 AX = 4
 CX = horizontal position
 DX = vertical position


 returns nothing


 - default cursor position is at the screen center
 - the position must be within the range of the current video mode
 - the position may be rounded to fit screen mode resolution

:int 33,5
^INT 33,5 - Get Mouse Button Press Information


 AX = 5
 BX = 0  left button
      1  right button


 on return:
 BX = count of button presses (0-32767), set to zero after call
 CX = horizontal position at last press
 DX = vertical position at last press
 AX = status:

    │F-8│7│6│5│4│3│2│1│0│  Button Status
      │  │ │ │ │ │ │ │ └──── left button (1 = pressed)
      │  │ │ │ │ │ │ └───── right button (1 = pressed)
      └──┴─┴─┴─┴─┴─┴────── unused

:int 33,6
^INT 33,6 - Get Mouse Button Release Information


 AX = 6
 BX = 0  left button
      1  right button


 on return:
 BX = count of button releases (0-32767), set to zero after call
 CX = horizontal position at last release
 DX = vertical position at last release
 AX = status

    │F-8│7│6│5│4│3│2│1│0│  Button status
      │  │ │ │ │ │ │ │ └──── left button (1 = pressed)
      │  │ │ │ │ │ │ └───── right button (1 = pressed)
      └──┴─┴─┴─┴─┴─┴────── unused

:int 33,7
^INT 33,7 - Set Mouse Horizontal Min/Max Position


 AX = 7
 CX = minimum horizontal position
 DX = maximum horizontal position


 returns nothing


 - restricts mouse horizontal movement to window
 - if min value is greater than max value they are swapped

:int 33,8
^INT 33,8 - Set Mouse Vertical Min/Max Position


 AX = 8
 CX = minimum vertical position
 DX = maximum vertical position


 returns nothing


 - restricts mouse vertical movement to window
 - if min value is greater than max value they are swapped

:int 33,9
^INT 33,9 - Set Mouse Graphics Cursor


 AX = 9
 BX = horizontal hot spot (-16 to 16)
 CX = vertical hot spot (-16 to 16)
 ES:DX = pointer to screen and cursor masks (16 byte bitmap)


 returns nothing


 - screen mask is AND'ed to screen Cursor Mask is XOR'ed
 - bytes 0-7 form the screen mask bitmap
 - bytes 8-F form the cursor mask bitmap

:int 33,a
^INT 33,A - Set Mouse Text Cursor


 AX = 0A
 BX = 00  software cursor
      01  hardware cursor
 CX = start of screen mask or hardware cursor scan line
 DX = end of screen mask or hardware cursor scan line


 returns nothing

:int 33,b
^INT 33,B - Read Mouse Motion Counters


 AX = 0B


 on return:
 CX = horizontal mickey count (-32768 to 32767)
 DX = vertical mickey count (-32768 to 32767)


 - count values are 1/200 inch intervals (1/200 in. = 1 mickey)

:int 33,c
^INT 33,C - Set Mouse User Defined Subroutine and Input Mask

 AX = 0C
 ES:DX = far pointer to user interrupt
 CX = user interrupt mask:

    │F-5│4│3│2│1│0│ user interrupt mask in CX
      │  │ │ │ │ └─── cursor position changed
      │  │ │ │ └──── left button pressed
      │  │ │ └───── left button released
      │  │ └────── right button pressed
      │  └─────── right button released
      └───────── unused

 returns nothing


 - routine at ES:DX is called if an event occurs and the
   corresponding bit specified in user mask is set
 - routine at ES:DX receives parameters in the following
   registers:

   AX = condition mask causing call
   CX = horizontal cursor position
   DX = vertical cursor position
   DI = horizontal counts
   SI = vertical counts
   DS = mouse driver data segment
   BX = button state:

      │F-2│1│0│
        │  │ └─── left button (1 = pressed)
        │  └──── right button (1 = pressed)
        └────── unused

 - initial call mask and user routine should be restore on exit
   from user program
 - user program may need to set DS to it's own segment
 - see   INT 33,14

:int 33,d
^INT 33,D - Mouse Light Pen Emulation On


 AX = 0D


 returns nothing


 - turns on light pen emulation;  the light pen is considered
   down when both buttons are down;   when both buttons are
   up the pen is considered off screen

 - see   INT 33,E

:int 33,e
^INT 33,E - Mouse Light Pen Emulation Off


 AX = 0E


 returns nothing


 - disables light pen emulation

 - see   INT 33,D

:int 33,f
^INT 33,F - Set Mouse Mickey Pixel Ratio


 AX = 0F
 CX = horizontal ratio (1..32767, default 8)
 DX = vertical ratio (1..32767, default 16)


 returns nothing


 - sets the ratio between physical cursor movement (mickeys) and
   screen coordinate changes
 - CX and DX must be unsigned (high bit must be 0)

:int 33,10
^INT 33,10 - Mouse Conditional OFF


 AX = 10h
 CX = upper X screen coordinate
 DX = upper Y screen coordinate
 SI = lower X screen coordinate
 DI = lower Y screen coordinate


 returns nothing


 - defines screen region for updating in which the mouse is hidden
   if found these coordinates (INT 33,1 must be used to turn cursor
   on again)

 - see  INT 33,1

:int 33,13
^INT 33,13 - Set Mouse Double Speed Threshold


 AX = 13h
 DX = threshold speed (mickeys per second, default 64)


 returns nothing


 - cursor speed is doubled when the cursor moves across the screen
   at the threshold speed

:int 33,14
^INT 33,14 - Swap Interrupt Subroutines

 AX = 14h
 ES:DX = far pointer to user routine
 CX = user interrupt mask:

    │F-8│7│6│5│4│3│2│1│0│ user interrupt mask in CX
      │  │ │ │ │ │ │ │ └─── cursor position changed
      │  │ │ │ │ │ │ └──── left button pressed
      │  │ │ │ │ │ └───── left button released
      │  │ │ │ │ └────── right button pressed
      │  │ │ │ └─────── right button released
      └──┴─┴─┴──────── unused

 on return:
 CX = previous user interrupt mask
 ES:DX = far pointer to previous user interrupt

 - routine at ES:DX is called if an event occurs and the
   corresponding bit specified in user mask is set
 - routine at ES:DX receives parameters in the following
   registers:

   AX = condition mask causing call
   CX = horizontal cursor position
   DX = vertical cursor position
   DI = horizontal counts
   SI = vertical counts
   DS = mouse driver data segment
   BX = button state:

      │F-2│1│0│
        │  │ └─── left button (1 = pressed)
        │  └──── right button (1 = pressed)
        └────── unused

 - initial call mask and user routine should be restore on exit
   from user program
 - user program may need to set DS to it's own segment
 - see   INT 33,C

:int 33,15
^INT 33,15 - Get Mouse Driver State and Memory Requirements


 AX = 15h


 on return
 BX = buffer size need to hold current mouse state


 - used before mouse functions 16h and 17h to determine memory
   needed to save mouse state before giving up control of mouse
   to another program

:int 33,16
^INT 33,16 - Save Mouse Driver State


 AX = 16h
 ES:DX = far pointer to mouse state save buffer


 returns nothing


 - used to save mouse information before relinquishing control
   to another programs mouse handler
 - see INT 33,15   INT 33,17

:int 33,17
^INT 33,17 - Restore Mouse Driver State


 AX = 17h
 ES:DX = far pointer to mouse state save buffer


 returns nothing


 - used to restore mouse information after regaining control
   from another programs mouse handler
 - see INT 33,15   INT 33,16

:int 33,18
^INT 33,18 - Set alternate subroutine call mask and address

 AX = 18h
 DX = offset to function
 CX = user interrupt mask:

    │F-8│7│6│5│4│3│2│1│0│ user interrupt mask in CX
      │  │ │ │ │ │ │ │ └─── alt key pressed during event
      │  │ │ │ │ │ │ └──── ctrl key pressed during event
      │  │ │ │ │ │ └───── shift key pressed during event
      │  │ │ │ │ └────── right button up event
      │  │ │ │ └─────── right button down event
      │  │ │ └──────── left button up event
      │  │ └───────── left button down event
      │  └────────── cursor moved
      └──────────── unused

 - entire mask is set to zero when INT 33,0 is called
 - up to three handlers may be defined with this call
 - mask should be cleared before program exit
 - when handler is called it receives parameters in the following
   registers:

   AX = condition mask causing call
   CX = horizontal cursor position
   DX = vertical cursor position
   DI = horizontal counts
   SI = vertical counts
   DS = mouse driver data segment
   BX = button state:

      │F-2│1│0│
        │  │ └─── left button (1 = pressed)
        │  └──── right button (1 = pressed)
        └────── unused

:int 33,19
^INT 33,19 - Get User Alternate Interrupt Address

 AX = 19h
 CX = user interrupt call mask (see below)


 on return:
 BX:DX = user interrupt vector
 CX = user interrupt call mask or zero if not found

    │F-8│7│6│5│4│3│2│1│0│ user interrupt mask in CX
      │  │ │ │ │ │ │ │ └─── alt key pressed during event
      │  │ │ │ │ │ │ └──── ctrl key pressed during event
      │  │ │ │ │ │ └───── shift key pressed during event
      │  │ │ │ │ └────── right button up event
      │  │ │ │ └─────── right button down event
      │  │ │ └──────── left button up event
      │  │ └───────── left button down event
      │  └────────── cursor moved
      └──────────── unused

 - returns vector to function defined by INT 33,18
 - searches the event handlers defined by INT 33,18 for a routine
   with a call mask matching CX

:int 33,1a
^INT 33,1A - Set Mouse Sensitivity


 AX = 1A
 BX = horizontal coordinates per pixel  (≤ 100)
 CX = vertical coordinates per pixel  (≤ 100)
 DX = double speed threshold


 returns nothing


 - sets mouse sensitivity by setting the ratio of the mouse
   coordinates per screen pixel
 - provides same results as calls to both INT 33,F and INT 33,13
 - these values are not reset by INT 33,0
 - see   INT 33,F    INT 33,13


:int 33,1b
^INT 33,1B - Get Mouse Sensitivity


 AX = 1B


 on return:
 BX = horizontal coordinates per pixel  (≤ 100)
 CX = vertical coordinates per pixel  (≤ 100)
 DX = double speed threshold


 - returns mouse sensitivity information as the number of mouse
   coordinates per screen pixel

:int 33,1c
^INT 33,1C - Set Mouse Interrupt Rate  (InPort only)


 AX = 1C
 BX = rate code
    = 0  no interrupts
    = 1  30 interrupts per second
    = 2  50 interrupts per second
    = 3  100 interrupts per second
    = 4  200 interrupts per second



 - work with the InPort mouse only
 - sets the rate the mouse status is polled by the mouse driver
 - faster rates provide better resolution but take away CPU time
 - values in BX > 4 can cause unpredicatable results

:int 33,1d
^INT 33,1D - Set Mouse CRT Page


 AX = 1D
 BX = CRT page number


 returns nothing


 - sets the CRT page which the mouse cursor is displayed
 - see VIDEO PAGES

:int 33,1e
^INT 33,1E - Get Mouse CRT Page


 AX = 1E


 on return:
 BX = CRT page number cursor is displayed on


 - see VIDEO PAGES

:int 33,1f
^INT 33,1F - Disable Mouse Driver


 AX = 1F


 on return:
 AX = 001F if successful
      FFFF if error
 ES:BX = previous INT 33 vector


 - restores vectors for INT 10 and INT 71 (8088/86) or INT 74 (286+)
 - INT 33 interrupt vector (software) is not affected
 - use of the vector returned in ES:BX to restore the previous INT 33
   vector can cause problems since it contains the value of INT 33
   before the driver was installed; any other hooks into INT 33 set
   after driver installation will not receive service

:int 33,20
^INT 33,20 - Enable Mouse Driver


 AX = 20h


 returns nothing


 - reinstalls the mouse drivers interrupt vectors for INT 10 and
   INT 71 (8088/86) and INT 74 (286/386)
 - see INT 33,1F

:int 33,21
^INT 33,21 - Reset Mouse Software

 AX = 21h

 on return:
 AX = 0021  mouse driver not installed
      FFFF  mouse driver installed
 BX = 2  mouse driver installed

 - similar to INT 33,0 but does not reset the mouse hardware or
   display variables
 - both AX and BX must be correct for successful reset
 - interrupt routines set through INT 33,18 are preserved
 - resets the mouse to the following defaults:

   .  mouse is positioned to screen center
   .  mouse cursor is reset and hidden
   .  no interrupts are enabled (mask = 0)
   .  double speed threshold set to 64 mickeys per second
   .  horizontal mickey to pixel ratio (8 to 8)
   .  vertical mickey to pixel ratio (16 to 8)
   .  max width and height are set to maximum for video mode

:int 33,22
^INT 33,22 - Set Language for Messages

 AX = 22h
 BX = language number (with /L switch value):
    = 0  English     n/a
    = 1  French      F
    = 2  Dutch       NL
    = 3  German      D
    = 4  Swedish     S
    = 5  Finnish     SF
    = 6  Spanish     E
    = 7  Portuguese  P
    = 8  Italian     I


 returns nothing


 - only works with international version of the mouse driver
 - see   INT 33,23
:int 33,23
^INT 33,23 - Get Language Number

 AX = 23h


 on return:
 BX = language number (with /L switch value):
    = 0  English     n/a
    = 1  French      F
    = 2  Dutch       NL
    = 3  German      D
    = 4  Swedish     S
    = 5  Finnish     SF
    = 6  Spanish     E
    = 7  Portuguese  P
    = 8  Italian     I

 - only works with international version of the mouse driver
 - returns English (0) if not international version

 - see   INT 33,22
:int 33,24
^INT 33,24 - Get Driver Version, Mouse Type & IRQ Number

 AX = 24h


 on return:
 BH = major version (see below)
 BL = minor version (see below)
 CH = mouse type:
    = 1  bus mouse
    = 2  serial mouse
    = 3  InPort mouse
    = 4  PS/2  mouse
    = 5  Hewlett Packard mouse
 CL = IRQ number:
    = 0  PS/2
    = 2  IRQ 2
    = 5  IRQ 5
    = 7  IRQ 7

 - version 6.1 would be represented as BH = 06h, BL = 10h
:int 4a
^INT 4A - RTC Alarm Handler Vector


 - not a true interrupt, but a pointer to an alarm handler routine
 - called by  INT 70  and enabled by INT 1A,6
 - routine must exit via IRET

:int 67:ems services
^INT 67 - Expanded Memory Specification

%Function requested in AH; see also  INT 67,N  where N is:

      40  Get EMM Status
      41  Get Page Frame Base Address
      42  Get Page Counts
      43  Get Handle and Allocate Pages
      44  Map Logical Page Into Physical Page Window
      45  Release Handle and Memory Pages
      46  Get EMM Version
      47  Save Page Map Context
      48  Restore Page Map Context
      49  Get I/O Port Addresses
      4A  Get Logical to Physical Page Mapping
      4B  Get Handle Count
      4C  Get Page Count for Handle
      4D  Get Page Count for All Handles
      4E  Get/Set Page Map Context
      4F  Get/Set Partial Page Map
      50  Map/Unmap Multiple Handle Pages
      51  Reallocate Pages
      52  Get/Set Handle Attributes
      53  Get/Set Handle Name
      54  Get Handle Directory
      55  Alter Page Map and Jump
      56  Alter Page Map and Call
      57  Move/Exchange Memory Region
      58  Get Mappable Physical Address Array
      59  Get Expanded Memory Hardware Information
      5A  Allocate Standard/Raw Pages
      5B  Alternate Map Register Set DMA Registers
      5C  Prepare Expanded Memory for Warm Boot
      5D  Enable/Disable OS Functions
      60  Get Physical Window Array


 - see   EMS STATUS

:int 67,40:ems status
^INT 67,40 - Get EMM Status  (LIM EMS 3.0+)

 AH = 40h

 on return:
 AH = status

      00  success
      80  internal software error
      81  hardware malfunction
      83  unallocated or invalid handle
      84  undefined function requested
      85  no handles available
      86  error in save or restore of mapping context
      87  more pages requested than physically exist
      88  more pages requested than currently available
      89  zero pages requested
      8A  invalid logical page number
      8B  illegal physical page number
      8C  context stack out of memory
      8D  context save failed, handle already has context stack
      8E  context restore failed, no context stack for handle
      8F  invalid subfunction
      90  undefined attribute type
      91  feature not supported
      92  success, portion of the source region was overwritten
      93  length of source or destination region exceeds length of
          region allocated to either source or destination handle
      94  conventional and expanded memory regions overlap
      95  offset within logical page exceeds size of logical page
      96  region length exceeds 1M
      97  source and destination regions have same handle and overlap
      98  memory source or destination type undefined
      9A  specified DMA register set not supported ???
          specified alternate map register set not supported
      9B  all DMA register sets currently allocated ???
          all alternate map register sets currently allocated
      9C  alternate DMA sets not supported ???
          alternate map register sets not supported
      9D  undefined or unallocated DMA register set ???
          undefined or unallocated alternate map register set
      9E  dedicated DMA channels not supported
      9F  specified dedicated DMA channel not supported
      A1  duplicate handle name
      A2  attempted to wrap around 1Mb conventional address space
      A3  contents of partial page map corrupted or count of
          mappable segments exceeds total mappable segments
      A4  operating system denied access


 - registers not listed are preserved
 - should only be used after establishing that the EMS driver
   is present
:int 67,41
^INT 67,41 - Get Page Frame Base Address  (LIM EMS 3.0+)


 AH = 41h


 on return:
 AH = 00 success
    = error code (see EMS STATUS)
 BX = segment of page frame (PFBA)


 - use this to determine where in the 1Mb memory address the page
   frame will be mapped
 - registers not listed are preserved

:int 67,42
^INT 67,42 - Get Page Counts  (LIM EMS 3.2+)


 AH = 42h


 on return:
 AH = 00  success
    = error code (see EMS STATUS)
 BX = number of unallocated or available pages
 DX = total number of pages in EMM system


 - registers not listed are preserved

:int 67,43
^INT 67,43 - Get Handle and Allocate Pages  (LIM EMS 3.2+)


 AH = 43h
 BX = number of logical pages to allocate


 on return:
 AH = 00  success
    = error code (see EMS STATUS)
 DX = EMM handle


 - handles not explicitly closed by the application are not
   recoverable on exit from the program
 - registers not listed are preserved

:int 67,44
^INT 67,44 - Map Logical Page Into Physical Page Window (LIM EMS)


 AH = 44h
 AL = physical page number (0-3)
 BX = logical page number (0 to total allocated minus 1)
 DX = EMM handle


 on return:
 AH = 00  success
    = error code (see EMS STATUS)


 - registers not listed are preserved

:int 67,45
^INT 67,45 - Release Handle and Memory Pages  (LIM EMS)


 AH = 45h
 DX = EMM handle


 on return:
 AH = 00 success
    = error code (see EMS STATUS)


 - handles must be explicitly freed by an application or the memory
   will not be available to the following applications
 - if unsuccessful, the operation should be retried
 - registers not listed are preserved

:int 67,46
^INT 67,46 - Get EMM Version  (LIM EMS)


 AH = 46h


 on return:
 AH = 00  success
    = error code (see EMS STATUS)
 AL = EMM version number in BCD


 - upper four bits of AL contain the BCD major version
 - lower four bits of AL contain the BCD minor version
 - registers not listed are preserved

:int 67,47
^INT 67,47 - Save Page Map Context  (LIM EMS 3.0+)


 AH = 47h
 DX = EMM handle assigned to the interrupt service routine
      servicing the interrupt


 on return:
 AH = 00  success
    = error code (see EMS STATUS)


 - any TSR, ISR or device driver using EMS should save contexts
   before manipulating EMS memory and restore contexts afterwards
 - registers not listed are preserved
 - see INT 67,48

:int 67,48
^INT 67,48 - Restore Page Map Context  (LIM EMS 3.0+)


 AH = 48h
 DX = EMM handle assigned to the interrupt service routine
      servicing the interrupt


 on return:
 AH = 00  success
    = error code (see EMS STATUS)


 - any TSR, ISR or device driver using EMS should save contexts
   before manipulating EMS memory and restore contexts afterwards
 - registers not listed are preserved

:int 67,49
^INT 67,49 - Get I/O Port Addresses  (LIM EMS ≤ 3.0)


 AH = 49h
 ES:DI = far pointer to storage array


 on return:
 AL = board count  (0 < AL <= 4)
 AH = 00 success
    = error code (see EMS STATUS)


 - defined in EMS 3.0, but undocumented in EMS 3.2;  new software
   should not use this function, but old software still works
 - registers not listed are preserved

:int 67,4a
^INT 67,4A - Get Logical to Physical Page Mapping  (LIM EMS ≤ 3.0)


 AH = 4A
 DX = EMS handle
 ES:DI far pointer to storage array


 on return:
 AH = 00  success
    = error code (see EMS STATUS)
 BX = contains count of entries placed in array at ES:DI


 - defined in EMS 3.0, but undocumented in EMS 3.2;  new software
   should not use this function, but old software still works
 - registers not listed are preserved

:int 67,4b
^INT 67,4B - Get Handle Count  (LIM EMS)


 AH = 4Bh


 on return:
 AH = 00  success
    = error code (see EMS STATUS)
 BX = number of currently active EMM handles (0-256)
      zero indicates EMS not in use


 - to determine the number of handles available subtract BX from 255
 - registers not listed are preserved

:int 67,4c
^INT 67,4C - Get Page Count for Handle  (LIM EMS)


 AH = 4Ch
 DX = EMM handle


 on return:
 AH = 00  success
    = error code (see EMS STATUS)
 BX = total allocated page count for handle (1-512)


 - a handle can refer to up to 512 logical pages
 - registers not listed are preserved

:int 67,4d
^INT 67,4D - Get Page Count for All Handles  (LIM EMS)

 AH = 4Dh
 ES:DI = pointer to handle array


 on return:
 AH = 00  success
    = error code (see EMS STATUS)
 BX = number of active EMM handles (0..255)
 ES:DI = pointer to an array of entries of the format:

    Offset  Size     Description
      00    word   EMS handle number
      02    word   number of pages

 - buffer at ES:DI should be able to hold an array of at least 4*BX
 - an error will occur if ES:DI points to a buffer that will
   cause a segment swap
 - registers not listed are preserved
:int 67,4e
^INT 67,4E - Get/Set Page Map Context  (LIM EMS 3.2+)

 AH = 4Eh
 AL = 00  get page mapping context into array
          ES:DI = pointer to destination array
      01  set page mapping context from array
          DS:SI = pointer to context source array
      02  get and set page mapping registers at once
          ES:DI = pointer to destination array
          DS:SI = pointer to context source array
      03  get size of page mapping array
      04-31  reserved


 on return:
 AH = 00  success
    = error code (see EMS STATUS)
 AL = bytes in pagemapping array (when AL=3)
 ES:DI = pointer to array with mapping info (AL=00/02)

 - an error will occur if ES:DI points to a buffer that will
   cause a segment swap
 - designed for use by multitasking operating systems only

:int 67,4f
^INT 67,4F - Get/Set Partial Page Map  (LIM EMS 4.0+)

 AH = 4Fh

 AL = 00  get partial page map
      DS:SI = pointer to structure containing list of segments whose
              mapping contexts are to be saved
      ES:DI = pointer to array to receive page map

 AL = 01  set partial page map
      DS:SI = pointer to structure containing saved partial page map

 AL = 02  get size of partial page map
      BX = number of mappable segments in the partial map to be saved


 on return:
 AH = 00  success
    = error code (see EMS STATUS)
 AL = size of partial page map (if AL=2)

:int 67,50
^INT 67,50 - Map/Unmap Multiple Handle Pages  (LIM EMS 4.0+)


 AH = 50h
 AL = 00 Map/unmap pages
    = 01 map/unmap segments
 DX = EMM handle
 CX = number of entries in array
 DS:SI = pointer to mapping array


 on return:
 AH = 00  success
    = error code (see EMS STATUS)

:int 67,51
^INT 67,51 - Reallocate Pages  (LIM EMS 4.0+)


 AH = 51h
 DX = EMM handle
 BX = number of pages to be allocated to handle


 on return:
 AH = 00  success
    = error code (see EMS STATUS)
 BX = actual number of pages allocated to handle

:int 67,52
^INT 67,52 - Get/Set Handle Attributes  (LIM EMS 4.0+)


 AH = 52h
 AL = 00  get handle attributes
      01  set handle attributes
      02  get attribute capability
 BL = new attribute (if AL=1)
 DX = EMM handle


 on return:
 AH = 00  success
    = error code (see EMS STATUS)
 AL = attribute (input AL=0)
      00  handle is volatile
      01  handle is nonvolatile
 AL = attribute capability (input AL=2)
      00  only volatile handles supported
      01  both volatile and nonvolatile supported

:int 67,53
^INT 67,53 Get/Set Handle Name  (LIM EMS 4.0+)


 AH = 53h
 AL = 00 get handle name
         ES:DI = pointer to 8byte handle name array

      01 set handle name
         DS:SI = pointer to 8byte handle name
         DX = EMM handle


 on return:
 AH = status  (see EMS STATUS)

:int 67,54
^INT 67,54 - Get Handle Directory  (LIM EMS 4.0+)


 AH = 54h
 AL = 00  get handle directory
          ES:DI = pointer to buffer for handle directory

      01  search for named handle
          DS:SI = pointer to 8byte name

      02  get total number of handles


 on return:
 AL = number of entries in handle directory (AL = 00h)
 DX = value of named handle (if AH was 01)
 BX = total number of handles (if AH was 02)
 AH = status  (see EMS STATUS)

:int 67,55
^INT 67,55 - Alter Page Map and Jump  (LIM EMS 4.0+)


 AH = 55h
 AL = 00  physical page numbers provided by caller
      01  segment addresses provided by caller
 DX = EMM handle
 DS:SI = pointer to structure with map and jump address


 on return:
 AH = status  (see EMS STATUS)

:int 67,56
^INT 67,56 - Alter Page Map and Call  (LIM EMS 4.0+)


 AH = 56h
 AL = 00  physical page numbers provided by caller
          DX = EMM handle
          DS:SI = pointer to structure with page map and call address
      01  segment addresses provided by caller
          DX = EMM handle
          DS:SI = pointer to structure with page map and call address
      02  get page map stack space required


 on return:
 BX = stack space required (AL = 02)
 AH = status  (see EMS STATUS)


 - if successful, the target address is called
 - use a RETF to return and restore mapping context

:int 67,57
^INT 67,57 - Move/Exchange Memory Region  (LIM EMS 4.0+)


 AH = 57h
 AL = 00  move memory region
      01  exchange memory region
 DS:SI = pointer to structure describing source and destination


 on return:
 AH = status  (see EMS STATUS)

:int 67,58
^INT 67,58 - Get Mappable Physical Address Array  (LIM EMS 4.0+)


 AH = 58h
 AL = 00  get mappable physical address array
          ES:DI = pointer to buffer to be filled with array
      01  get number of entries in m.p.a. array


 on return:
 CX = number of entries in array
 AH = status  (see EMS STATUS)

:int 67,59
^INT 67,59 - Get Expanded Memory Hardware Information (LIM EMS 4.0+)


 AH = 59h
 AL = 00  get hardware configuration array
          ES:DI = pointer to buffer to be filled with array
      01  get unallocated raw page count


 on return:
 BX = unallocated raw pages (AL = 01)
 DX = total raw pages (AL = 01)
 AH = status  (see EMS STATUS)


 - subfunction 00 is for use by operating systems only; can be
   enabled or disabled at any time by the operating system

:int 67,5a
^INT 67,5A - Allocate Standard/Raw Pages  (LIM EMS 4.0+)


 AH = 5A
 AL = 00  allocate standard pages
      01  allocate raw pages
 BX = number of pages to allocate


 on return:
 DX = EMM handle
 AH = status  (see EMS STATUS)

:int 67,5b
^INT 67,5B - Alternate Map Register Set  (LIM EMS 4.0+)

 AH = 5B
 AL = 00  get alternate map register set
      01  set alternate map register set
          BL = new alternate map register set number
          ES:DI = pointer to map register context save area if BL=0
      02  get alternate map save array size
      03  allocate alternate map register set
      04  deallocate alternate map register set
          BL = number of alternate map register set
      05  allocate DMA register set
      06  enable DMA on alternate map register set
          BL = DMA register set number
          DL = DMA channel number
      07  disable DMA on alternate map register set
          BL = DMA register set number
      08  deallocate DMA register set
          BL = DMA register set number

 on return:
 AH = status  (see EMS STATUS)
 BL = active alternate map register set number if nonzero (AL=0)
    = number of alternate map register set; 0 if not supported (AL=3)
    = DMA register set number; zero if not supported (AL = 05)
 DX = array size in bytes (AL = 02)
 ES:DI = pointer to a map register context save area if BL=0 (AL=0)


 - for use by operating systems only; can be enabled or disabled
   at any time by the operating system

:int 67,5c
^INT 67,5C - Prepare Expanded Memory for Warm Boot  (LIM EMS 4.0+)

 AH = 5C


 on return:
 AH = status  (see EMS STATUS)

:int 67,5d
^INT 67,5D - Enable/Disable OS Functions  (LIM EMS 4.0+)


 AH = 5D
 AL = 00  enable OS function Set
      01  disable OS function Set
      02  return access key
 BX,CX = access key returned by first invocation


 on return:
 AH = status  (see EMS STATUS)
 BX,CX = access key, returned only on first invocation of function


 - function 2 resets memory manager, returns access key at next
   invocation

:int 67,60
^INT 67,60 - LIM EMS Get Physical Window Array


 AH = 60h
 ES:DI = pointer to physical window array


 on return:
 AH = 00  success
    = error status  (see EMS STATUS)

:int 70
^INT 70 - Real Time Clock Interrupt  (XT 286,AT,PS2)


 - called 1024 times per second for periodic and alarm functions
 - decrements a DWORD counter by 976µ sec (1/1024)
 - when DWORD reaches zero, bit 7 of designated wait flag is set
 - if alarm was enabled by  INT 1A,6  INT 4A  is called when counter
   reaches zero to activate alarm handler
 - not available in model 30 PS2


 - see   INT 15,83   INT 15,86