INTERRUP.TXT

@Interrupt Services DOSùBIOSùEMSùMouse
: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 or COM4 service required, (COM3-COM8 on MCA PS/2)
	IRQ4	 C	COM1 or COM3 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 (PS/2 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, simple ~IRET~ in DOS 2.0-5.0
	2C	DOS	internal, simple IRET in DOS 2.0-5.0
	2D	DOS	internal, simple IRET in DOS 2.0-5.0
	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)
	31	DPMI	DOS Protected Mode Interface (for DOS extenders)
	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,PS/2) (see ~INT 4A~)
	4B-4F	BIOS	reserved
	50	BIOS	periodic alarm from timer (PS/2)
	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 18
	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:

	50:00	= 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,PS/2)
	40:97 = updates keyboard LED flags (AT,PS/2)
	FFFF:0 = reboot code called if Ctrl-Alt-Del pressed

%	related interrupts:

	~INT 5~     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

%	For more information, see the following topics:

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

	- registers CS, DS, ES, SS, BX, CX, DX are preserved unless
	  explicitly changed
	- 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 scan lines are zero based
	- cursor size can also be set via the ~6845~ CRT controller
	- cursor size can be determined using the CRTC,  ~INT 10,3~  or the
	  ~BIOS Data Area~ bytes 40:60 (ending scan line) and 40:61 (starting
	  scan line)
	- the following is a list of the cursor scan lines associated with
	  most common adapters;  screen sizes over 40 lines may differ
	  depending on adapters.

%		Line	 Starting     Ending	  Character
%	Video	Count	 Scan Line    Scan Line   Point Size

	CGA	 25	    06		 07	      08
	MDA	 25	    0B		 0C	      0E
	EGA	 25	    06		 07	      0E
	EGA	 43	  04/06 	 07	      08
	VGA	 25	    0D		 0E	      10
	VGA	 40	    08		 09	      0A
	VGA	 50	    06		 07	      08

	- use CX = 2000h to disable cursor

: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 uses coordinates 0,0 to 24,79;	40x25 uses 0,0 to 24,39
	- the ~6845~ can also be used to perform this function
	- setting the data in the BIOS Data Area at location 40:50 does not
	  take immediate effect and is not recommended
	- see	~VIDEO PAGES~   ~6845~   ~BDA~

: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~ locations 40:50, 40:60 and 40:61
	- the ~6845~ can also be used to read the cursor position
	- the return data can be circumvented by direct port I/O to the 6845
	  CRT Controller since this function returns the data found in the
	  BIOS Data Area without actually checking the controller
	
: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
	- PS/2'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

: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, see ~VIDEO PAGES~
	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
	- this function is known to destroy AX and possibly SI and DI on
	  on some PS/2 VGA systems

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


	AH = 0D
	BH = page number, see ~VIDEO PAGES~
	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

: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 adapters this function can disable the video signal while
	  performing the output which causes 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 (PS/2)
	   BL = palette register to read (0-15)

	on return:
	  BH = value of palette register


%	AL = 08  read border color (overscan register, PS/2)

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


%	AL = 09  read palette registers and border (PS/2)
	   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 (PS/2)
	   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  PS/2 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):

	³7³6³5³4³3³2³1³0³  AL
	 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 0=don't move cursor, 1=move cursor
	 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ 0=BL has attributes, 1=string has attributes
	 ÀÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄ 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:

		³7³6³5³4³3³2³1³0³ State Information byte at offset 2D
		 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1 = all modes active (MCGA always 0)
		 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = gray scale summing enabled
		 ³ ³ ³ ³ ³ ÀÄÄÄÄÄ 1 = monochrome display attached
		 ³ ³ ³ ³ ÀÄÄÄÄÄÄ 1 = default palette loading disabled
		 ³ ³ ³ ÀÄÄÄÄÄÄÄ 1 = cursor emulation enabled
		 ³ ³ ÀÄÄÄÄÄÄÄÄ 1 = blinking attribute enabled
		 ÀÄÁÄÄÄÄÄÄÄÄÄ 1 = reserved

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

		³7³6³5³4³3³2³1³0³ Save Area Status
		 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1 = two text char sets are active
		 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = dynamic save area is active
		 ³ ³ ³ ³ ³ ÀÄÄÄÄÄ 1 = text char set override is active
		 ³ ³ ³ ³ ÀÄÄÄÄÄÄ 1 = graphics char set is override active
		 ³ ³ ³ ÀÄÄÄÄÄÄÄ 1 = palette override is active
		 ³ ³ ÀÄÄÄÄÄÄÄÄ 1 = display combination code ext. active
		 ÀÄÁÄÄÄÄÄÄÄÄÄ 1 = reserved

	33  dword   reserved


^Video BIOS Static Functionality Table	(EGA/VGA)

		³7³6³5³4³3³2³1³0³ Video modes supported, byte at offset 00
		 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1 = mode 0
		 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = mode 1
		 ³ ³ ³ ³ ³ ÀÄÄÄÄÄ 1 = mode 2
		 ³ ³ ³ ³ ÀÄÄÄÄÄÄ 1 = mode 3
		 ³ ³ ³ ÀÄÄÄÄÄÄÄ 1 = mode 4
		 ³ ³ ÀÄÄÄÄÄÄÄÄ 1 = mode 5
		 ³ ÀÄÄÄÄÄÄÄÄÄ 1 = mode 6
		 ÀÄÄÄÄÄÄÄÄÄÄ 1 = mode 7

		³7³6³5³4³3³2³1³0³ Video modes supported, byte at offset 01
		 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1 = mode 8
		 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = mode 9
		 ³ ³ ³ ³ ³ ÀÄÄÄÄÄ 1 = mode A
		 ³ ³ ³ ³ ÀÄÄÄÄÄÄ 1 = mode B
		 ³ ³ ³ ÀÄÄÄÄÄÄÄ 1 = mode C
		 ³ ³ ÀÄÄÄÄÄÄÄÄ 1 = mode D
		 ³ ÀÄÄÄÄÄÄÄÄÄ 1 = mode E
		 ÀÄÄÄÄÄÄÄÄÄÄ 1 = mode F

		³7³6³5³4³3³2³1³0³ Video modes supported, byte at offset 02
		 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1 = mode 10
		 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = mode 11
		 ³ ³ ³ ³ ³ ÀÄÄÄÄÄ 1 = mode 12
		 ³ ³ ³ ³ ÀÄÄÄÄÄÄ 1 = mode 13
		 ÀÄÁÄÁÄÁÄÄÄÄÄÄÄ reserved

	03  dword  reserved
	07  byte   scan lines supported in text modes

		³7³6³5³4³3³2³1³0³ Scan lines supported, byte at offset 07
		 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1 = 200 lines
		 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = 350 lines
		 ÀÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄ 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

		³7³6³5³4³3³2³1³0³ Other flags, byte at offset 0A
		 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1 = all modes (0 on MCGA)
		 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = gray scale summing
		 ³ ³ ³ ³ ³ ÀÄÄÄÄÄ 1 = character set loading
		 ³ ³ ³ ³ ÀÄÄÄÄÄÄ 1 = default palette loading
		 ³ ³ ³ ÀÄÄÄÄÄÄÄ 1 = cursor emulation
		 ³ ³ ÀÄÄÄÄÄÄÄÄ 1 = 64 color palette
		 ³ ÀÄÄÄÄÄÄÄÄÄ 1 = video DAC loading
		 ÀÄÄÄÄÄÄÄÄÄÄ 1 = DAC controlled by ACCS

	0B  byte   other capability flags

		³7³6³5³4³3³2³1³0³ Other flags, byte at offset 0B
		 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1 = light pen support
		 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = save/restore video state
		 ³ ³ ³ ³ ³ ÀÄÄÄÄÄ 1 = blinking/background intensity
		 ³ ³ ³ ³ ÀÄÄÄÄÄÄ 1 = display combination code
		 ÀÄÁÄÁÄÁÄÄÄÄÄÄÄ reserved

	0C  word   reserved
	0E  byte   save area capabilities

		³7³6³5³4³3³2³1³0³  save area capabilities at offset 0E
		 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = multiple text character sets
		 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ 1 = dynamic save area
		 ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄ 1 = text character set override
		 ³ ³ ³ ³ ÀÄÄÄÄÄÄÄ 1 = graphics character set override
		 ³ ³ ³ ÀÄÄÄÄÄÄÄÄ 1 = palette override
		 ³ ³ ÀÄÄÄÄÄÄÄÄÄ 1 = display combination code extension
		 ÀÄÁÄÄÄÄÄÄÄÄÄÄ 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:

	³F³E³D³C³B³A³9³8³7³6³5³4³3³2³1³0³  AX
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ IPL diskette installed
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ math coprocessor
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÄÄÄÄÄ old PC system board RAM < 256K
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ pointing device installed (PS/2)
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄ not used on PS/2
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÄÄÄÄÄÄ initial video mode
	 ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÄÄÄÄÄÄÄÄÄ # of diskette drives, less 1
	 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄ 0 if DMA installed
	 ³ ³ ³ ³ ÀÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄ number of serial ports
	 ³ ³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ game adapter installed
	 ³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ unused, internal modem (PS/2)
	 ÀÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 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 Area~ 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

^For more information see the following topics:

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


	Ø  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)

	- registers DS, BX, CX and DX are preserved
	- 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):

	  ³F³E³D³C³B³A³9³8³7³6³5-0³  CX
	   ³ ³ ³ ³ ³ ³ ³ ³ ³ ³	ÀÄÄÄÄÄ	sector number
	   ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÄÄÄÄÄÄ  high order 2 bits of track/cylinder
	   ÀÄÁÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄ  low order 8 bits of track/cyl number

	- see	~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):

	  ³F³E³D³C³B³A³9³8³7³6³5-0³  CX
	   ³ ³ ³ ³ ³ ³ ³ ³ ³ ³	ÀÄÄÄÄÄ	sector number
	   ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÄÄÄÄÄÄ  high order 2 bits of track/cylinder
	   ÀÄÁÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄ  low order 8 bits of track/cyl number

	- see	~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):

	  ³F³E³D³C³B³A³9³8³7³6³5-0³  CX
	   ³ ³ ³ ³ ³ ³ ³ ³ ³ ³	ÀÄÄÄÄÄ	sector number
	   ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÄÄÄÄÄÄ  high order 2 bits of track/cylinder
	   ÀÄÁÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄ  low order 8 bits of track/cyl number

	- see	~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):

	³F³E³D³C³B³A³9³8³7³6³5-0³  CX (cylinder value 0-1023 dec.)
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³  ÀÄÄÄÄÄ  unused
	 ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÄÄÄÄÄÄ	high order 2 bits of track/cylinder
	 ÀÄÁÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄ  low order 8 bits of track/cyl number

: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
: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
: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 - 5¬  360K	     03 - 3«  720K
	     02 - 5¬  1.2Mb	     04 - 3« 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

	³F³E³D³C³B³A³9³8³7³6³5³4³3³2³1³0³  CX
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÁÄÁÄÄ  sectors per track
	 ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÄÄÄÄÄÄÄÄÄ	high order 2 bits of cylinder count
	 ÀÄÁÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄ  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, PS/2 and later systems, but all hard disk
	  systems since the XT have this function available
	- only the disk number is checked for validity
: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, PS/2 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:


		³7³6³5³4³3³2³1³0³  Control byte
		 ³ ³ ³ ³ ³ ÀÄÁÄÁÄÄÄÄ drive option
		 ³ ³ ÀÄÁÄÁÄÄÄÄÄÄÄÄÄ always zero
		 ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄ disable ECC retries
		 ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ disable access retires
: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, PS/2 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):

	  ³F³E³D³C³B³A³9³8³7³6³5³4³3³2³1³0³  CX
	   ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÁÄÁÄÄÄÄ	sector number
	   ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÄÄÄÄÄÄÄÄÄÄÄ  high order 2 bits of track number
	   ÀÄÁÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄ	low order 8 bits of track number

	- see	~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, PS/2 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):

	  ³F³E³D³C³B³A³9³8³7³6³5³4³3³2³1³0³  CX
	   ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÁÄÁÄÄÄÄ	sector number
	   ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÄÄÄÄÄÄÄÄÄÄÄ  high order 2 bits of track number
	   ÀÄÁÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄ	low order 8 bits of track number

	- see	~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, PS/2 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):

	  ³F³E³D³C³B³A³9³8³7³6³5-0³  CX
	   ³ ³ ³ ³ ³ ³ ³ ³ ³ ³	ÀÄÄÄÄÄ	unused
	   ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÄÄÄÄÄÄ  high order 2 bits of track number
	   ÀÄÁÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄ  low order 8 bits of track number
: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, PS/2 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
: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
: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
: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, PS/2 and later systems, but all hard disk
	  systems since the XT have this function available
: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, PS/2 and later systems, but all hard disk
	  systems since the XT have this function available
: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
: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
: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, PS/2 and later systems, but all hard disk
	  systems since the XT have this function available
	- not valid on PS/2 model 30
: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 - 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 (PS/2)
		 1.44Mb diskette in 1.44Mb drive (PS/2)
	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 PS/2 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):

	  ³F³E³D³C³B³A³9³8³7³6³5³4³3³2³1³0³  CX
	   ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÁÄÁÄÄÄÄ	sectors per track count
	   ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÄÄÄÄÄÄÄÄÄÄÄ  high order 2 bits track/cyl count
	   ÀÄÁÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄ	low order 8 bits of track/cyl count

	- see	~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 PS/2 machines
:int 13,1a
^INT 13,1A - Format Unit (PS/2 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

		³7³6³5³4³3³2³1³0³  Format Unit Modifier Bits
		 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1=ignore primary defect map, 0=use map
		 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ 1=ignore secondary defect map, 0=use map
		 ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄ 1=update secondary defect map, 0=don't
		 ³ ³ ³ ³ ÀÄÄÄÄÄÄÄ 1=do extended surface analysis, 0=don't
		 ³ ³ ³ ÀÄÄÄÄÄÄÄÄ 1=periodic interrupt status on, 0=off
		 ÀÄÁÄÁÄÄÄÄÄÄÄÄÄ 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

%	For more information, see the following topics:

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


	- all functions have:
	  AH = function number
	  AL = character to send or receive
	  DX = zero based RS232 card number
	- all registers are preserved except AX
	- 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)

		³7³6³5³4³3³2³1³0³  AL  modem status
		 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ clear to send status changed
		 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ data set ready status changed
		 ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄ trailing edge ring indicator
		 ³ ³ ³ ³ ÀÄÄÄÄÄÄÄ receive line signal changed
		 ³ ³ ³ ÀÄÄÄÄÄÄÄÄ clear to send
		 ³ ³ ÀÄÄÄÄÄÄÄÄÄ data set ready
		 ³ ÀÄÄÄÄÄÄÄÄÄÄ ring indicator
		 ÀÄÄÄÄÄÄÄÄÄÄÄ receive line signal detected

		³7³6³5³4³3³2³1³0³  AH  port status
		 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ data ready
		 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ overrun error
		 ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄ parity error
		 ³ ³ ³ ³ ÀÄÄÄÄÄÄÄ framing error
		 ³ ³ ³ ÀÄÄÄÄÄÄÄÄ break detect
		 ³ ³ ÀÄÄÄÄÄÄÄÄÄ transmit holding register empty
		 ³ ÀÄÄÄÄÄÄÄÄÄÄ transmit shift register empty
		 ÀÄÄÄÄÄÄÄÄÄÄÄ 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)

	³7³6³5³4³3³2³1³0³  AL			   Parity (bits 4 & 3)
	 ³ ³ ³ ³ ³ ³ ÀÄÁÄÄÄÄ word length bits	       00 = none
	 ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄÄ stop bits flag	       01 = odd
	 ³ ³ ³ ÀÄÁÄÄÄÄÄÄÄÄ parity bits		       10 = none
	 ÀÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄ 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 14,3~ 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
: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 14,3~ 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
: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

	- for status bits see ~INT 14,STATUS~
	- the status check performs a poll of the port and does not
	  perform character I/O
:int 14,4
^INT 14,4 - Serial Port Extended Initialization (PS/2 & later systems)

	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		       1« 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 (PS/2 & later systems)

	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

		³7³6³5³4³3³2³1³0³	BL
		 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = activate data terminal ready
		 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ 1 = activate request to send
		 ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄ OUT1
		 ³ ³ ³ ³ ÀÄÄÄÄÄÄÄ OUT2
		 ³ ³ ³ ÀÄÄÄÄÄÄÄÄ 0 = normal, 1 = loopback test
		 ÀÄÁÄÁÄÄÄÄÄÄÄÄÄ reserved, forced to zero

	on return:
	AH = port status
	AL = modem status
	BL = ~UART~ modem control register

	- for status bits see ~INT 14,STATUS~

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

^For more information see the following topics:

	 ~INT 15,0~  Turn cassette motor on (PC,PCjr only)
	 ~INT 15,1~  Turn cassette motor off (PC,PCjr only)
	 ~INT 15,2~  Read blocks from cassette (PC,PCjr only)
	 ~INT 15,3~  Write blocks to cassette (PC,PCjr only)
	 ~INT 15,F~  PS/2 format periodic interrupt (PS/2 only)
	~INT 15,20~  PRINT.COM Critical region flag (undocumented DOS 3.x+)
	~INT 15,21~  PS/2 power on self test (PS/2 except 30)
	~INT 15,40~  Read / modify profiles (convertible only)
	~INT 15,41~  Wait on external event (convertible only)
	~INT 15,42~  Request system power off (convertible only)
	~INT 15,43~  Read system status (convertible only)
	~INT 15,44~  (De)activate internal modem power (convertible)
	~INT 15,4F~  Keyboard intercept  (BIOS date specific)
	~INT 15,80~  Device open
	~INT 15,81~  Device close
	~INT 15,82~  Program termination
	~INT 15,83~  Event wait
	~INT 15,84~  Joy-Stick support
	~INT 15,85~  System request key pressed
	~INT 15,86~  Elapsed time wait (AT and after)
	~INT 15,87~  Move block to/from extended memory
	~INT 15,88~  Extended memory size determination
	~INT 15,89~  Switch processor to protected mode
	~INT 15,90~  Device busy
	~INT 15,91~  Interrupt complete
	~INT 15,C0~  Return system configuration parameters (PS/2 only)
	~INT 15,C1~  Return extended BIOS data address (PS/2 only)
	~INT 15,C2~  Pointing device BIOS interface (PS/2 only)
	~INT 15,C3~  Enable/Disable watchdog timer
	~INT 15,C4~  Programmable option select


	- CF is set and AX is left unchanged if a function requested in AH
	  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 (PS/2 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-PS/2 CF=1 and AH contains the following
	  AH = 80h  for PC and PCjr
	     = 86h  on most other machines
:int 15,20
^INT 15,20 - PRINT.COM Critical Region Flag (undocumented DOS 3.x+)

	AH = 20h
	AL = 00  disable user critical region flag
	   = 01  enable user critical region flag
	ES:BX = pointer to user critical region flag byte (AH = 1)


	returns nothing


	- provides PRINT.COM with the address of a byte to increment on
	  entry to DOS functions
	- see ~bibliography~ reference for "Undocumented DOS"
:int 15,21
^INT 15,21 - Power On Self Test (POST) Error Log  (PS/2 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:

		³7³6³5³4³3³2³1³0³  AL
		 ³ ³ ³ ³ ³ ÀÄÁÄÁÄÄÄÄ conditions (codes) to wait for
		 ³ ³ ³ ³ ÀÄÄÄÄÄÄÄÄÄ reserved
		 ³ ³ ³ ÀÄÄÄÄÄÄÄÄÄÄ 1=port address/0=user byte
		 ÀÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄ 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:

		³7³6³5³4³3³2³1³0³  AL
		 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ LCD detached
		 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ reserved
		 ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄ RS232/parallel powered on
		 ³ ³ ³ ³ ÀÄÄÄÄÄÄÄ internal modem powered on
		 ³ ³ ³ ÀÄÄÄÄÄÄÄÄ power activated by alarm
		 ³ ³ ÀÄÄÄÄÄÄÄÄÄ standby power lost
		 ³ ÀÄÄÄÄÄÄÄÄÄÄ external power in use
		 ÀÄÄÄÄÄÄÄÄÄÄÄ 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, PS/2 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, PS/2 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, PS/2 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 (PS/2)
	CX,DX = number of microseconds to wait (976 æs 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 PS/2'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 PS/2)


	AH = 86h
	CX,DX = number of microseconds to wait (976 æs 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 PS/2 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
: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
: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 (PS/2)
	   = 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 (PS/2)
	   = 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 (PS/2 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

	³7³6³5³4³3³2³1³0³  Feature Byte
	 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ reserved
	 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ 0=PC bus, 1=Micro Channel
	 ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄ Extended BIOS Data Area (~EBDA~)allocated
	 ³ ³ ³ ³ ÀÄÄÄÄÄÄÄ wait for external event supported
	 ³ ³ ³ ÀÄÄÄÄÄÄÄÄ ~INT 15,4F~ used (kbd intercept)
	 ³ ³ ÀÄÄÄÄÄÄÄÄÄ ~RTC~ present
	 ³ ÀÄÄÄÄÄÄÄÄÄÄ 2nd ~8259~ present
	 ÀÄÄÄÄÄÄÄÄÄÄÄ DMA channel 3 used by fixed disk BIOS

	- see	~MACHINE ID~

:int 15,c1
^INT 15,C1 - Return Extended BIOS Data Area Segment (PS/2 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 PS/2


	- the EBDA is used internally by the PS/2 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  (PS/2 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  (PS/2)

	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 PS/2 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  (PS/2)

	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 PS/2 Programmable Option Select registers
	- available on 80286 and 80386 PS/2's

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


^For more information, see the following topics:

	~INT 16,0~   Wait for keystroke and read
	~INT 16,1~   Get keystroke status
	~INT 16,2~   Get shift status
	~INT 16,3~   Set keyboard typematic rate (AT+)
	~INT 16,4~   Keyboard click adjustment (AT+)
	~INT 16,5~   Keyboard buffer write  (AT,PS/2 enhanced keyboards)
	~INT 16,10~  Wait for keystroke and read  (AT,PS/2 enhanced keyboards)
	~INT 16,11~  Get keystroke status  (AT,PS/2 enhanced keyboards)
	~INT 16,12~  Get shift status  (AT,PS/2 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
	- all registers are preserved except AX and FLAGS
	- 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)

		³7³6³5³4³3³2³1³0³  AL or BIOS Data Area 40:17
		 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ right shift key depressed
		 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ left shift key depressed
		 ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄ CTRL key depressed
		 ³ ³ ³ ³ ÀÄÄÄÄÄÄÄ ALT key depressed
		 ³ ³ ³ ÀÄÄÄÄÄÄÄÄ scroll-lock is active
		 ³ ³ ÀÄÄÄÄÄÄÄÄÄ num-lock is active
		 ³ ÀÄÄÄÄÄÄÄÄÄÄ caps-lock is active
		 ÀÄÄÄÄÄÄÄÄÄÄÄ insert is active
: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 PS/2 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 PS/2 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 PS/2 machines with extended keyboard support
	- similar to ~INT 16,0~
: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 PS/2 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)

		³7³6³5³4³3³2³1³0³  AH
		 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ left CTRL key depressed
		 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ left ALT key depressed
		 ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄ right CTRL key pressed
		 ³ ³ ³ ³ ÀÄÄÄÄÄÄÄ right ALT key depressed
		 ³ ³ ³ ÀÄÄÄÄÄÄÄÄ scroll-lock depressed
		 ³ ³ ÀÄÄÄÄÄÄÄÄÄ num-lock key depressed
		 ³ ÀÄÄÄÄÄÄÄÄÄÄ caps-lock key depressed
		 ÀÄÄÄÄÄÄÄÄÄÄÄ system request key depressed

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

		³7³6³5³4³3³2³1³0³  AL
		 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ right shift key depressed
		 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ left shift key depressed
		 ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄ CTRL key depressed
		 ³ ³ ³ ³ ÀÄÄÄÄÄÄÄ ALT key depressed
		 ³ ³ ³ ÀÄÄÄÄÄÄÄÄ scroll-lock is active
		 ³ ³ ÀÄÄÄÄÄÄÄÄÄ num-lock is active
		 ³ ÀÄÄÄÄÄÄÄÄÄÄ caps-lock is active
		 ÀÄÄÄÄÄÄÄÄÄÄÄ insert is active


	- available on AT and PS/2 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

%	For more information, see the following topics:

	~INT 17,0~   Print character
	~INT 17,1~   Initialize printer port
	~INT 17,2~   Read printer port status

	Status flags returned in register AH

	³7³6³5³4³3³2³1³0³  AH (status)
	 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ  time-out
	 ³ ³ ³ ³ ³ ÀÄÁÄÄÄÄÄ  unused
	 ³ ³ ³ ³ ÀÄÄÄÄÄÄÄÄ  1 = I/O error  (~parallel~ pin 15)
	 ³ ³ ³ ÀÄÄÄÄÄÄÄÄÄ  1 = printer selected/on-line  (parallel pin 13)
	 ³ ³ ÀÄÄÄÄÄÄÄÄÄÄ  1 = out of paper  (parallel pin 12)
	 ³ ÀÄÄÄÄÄÄÄÄÄÄÄ  1 = printer acknowledgment  (parallel pin 10)
	 ÀÄÄÄÄÄÄÄÄÄÄÄÄ	1 = printer not busy  (parallel pin 11)

	- on the AT, XT 286, and PS/2 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.
	- all registers are preserved except AH
: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, see ~INT 17,STATUS~


	- writes character and returns status
:int 17,1
^INT 17,1 - Initialize Printer Port


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


	on return:
	AH = status, see ~INT 17,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

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

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


	on return:
	AH = status:

		³7³6³5³4³3³2³1³0³  Printer status bits
		 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ time out
		 ³ ³ ³ ³ ³ ÀÄÁÄÄÄÄÄ unused
		 ³ ³ ³ ³ ÀÄÄÄÄÄÄÄÄ I/O error
		 ³ ³ ³ ÀÄÄÄÄÄÄÄÄÄ selected
		 ³ ³ ÀÄÄÄÄÄÄÄÄÄÄ out of paper
		 ³ ÀÄÄÄÄÄÄÄÄÄÄÄ acknowledge
		 ÀÄÄÄÄÄÄÄÄÄÄÄÄ 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


%	For more informations, see the following topics:

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

	- function is specified in register AH
	- 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
	- this function can be called in a program to assure the date is
	  updated after midnight;  this will avoid the passing two midnights
	  date problem
: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,PS/2)


	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
:int 1a,3
^INT 1A,3 - Set Time on Real Time Clock  (XT 286,AT,PS/2)


	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,PS/2)


	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

	- calling this interrupt will update the DOS maintained date and
	  reset the ~BIOS Data Area~ date rollover flag at 40:70
	- see	~RTC~
:int 1a,5
^INT 1A,5 - Set Real Time Clock Date  (XT 286,AT,PS/2)


	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,PS/2)


	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
:int 1a,7
^INT 1A,7 - Disable Real Time Clock Alarm  (XT,AT,PS/2)


	AH = 07


	returns nothing


	- should be called previous to setting or resetting the
	  ~RTC~ alarm with ~INT 1A,6~
: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,PS/2)


	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 (PS/2)


	AH = 0Ah


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

:int 1a,b
^INT 1A,B - Set System Day Counter (PS/2)


	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:Ctrl-Break: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 23~.
	- 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
:int 1c:user timer routine
^INT 1C - System Timer Tick (User Routine)


	- called by ~INT 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
: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  ³7³6³5³4³3³2³1³0³  Disk Controller Mode byte 1
	       ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÄÄÄ  head step rate in milliseconds (0-F)
	       ÀÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄ  head unload time in milliseconds (0-F)

	  01  ³7³6³5³4³3³2³1³0³  Disk Controller Mode byte 2
	       ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ DMA flag (0 = use DMA)
	       ÀÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄ (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 topics 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, ~Ctrl-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 ~FCB~s
	- this function is no longer recommended, but can be used by
	  version of DOS before 2.0, see  ~INT 21,4C~  and  ~INT 21,0~

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

^For more information, see the following topics:

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


	- 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, ~Ctrl-Break~, and critical error
	  exit addresses, flushes all buffers, frees memory
	  and returns to DOS via the termination handler address
	- does not close ~FCB~s
	- this function is no longer recommended, but can be used by
	  version of DOS before 2.0, see  ~INT 21,4C~  and  ~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 23~ 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 23~ 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 23~ 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 23~ is executed

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

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

	³ max ³ count ³  BUFFER (N bytes)
	   ³	  ³	     ÀÄÄÄÄÄÄ input buffer
	   ³	  ÀÄÄÄÄÄÄÄÄÄÄÄÄ number of characters returned (byte)
	   ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 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 23~ 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 21,1~,  ~INT 21,6~,  ~INT 21,7~,  ~INT 21,8~ & ~INT 21,A~

: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
: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~

: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
: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
: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
: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
: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~
: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 (~DTA~)


	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
	- see	~INT 21,2F~
: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  ~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  ~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
	- calls ~INT 21,32~ with DL=00 for DOS version 2.x+
: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 also ~INT 21,55~

: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 filespec to parse
	ES:DI = pointer to a buffer for unopened ~FCB~


	Bit patterns for parsing control found in AL:

	³7³6³5³4³3³2³1³0³  AL
	 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = ignore leading separators
	 ³ ³ ³ ³ ³ ³ ³	     0 = don't ignore leading separators
	 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ 1 = modify drive ID if specified
	 ³ ³ ³ ³ ³ ³	    0 = modify drive ID regardless
	 ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄ 1 = modify filename if specified
	 ³ ³ ³ ³ ³	   0 = modify filename regardless
	 ³ ³ ³ ³ ÀÄÄÄÄÄÄÄ 1 = modify extension if specified
	 ³ ³ ³ ³	  0 = modify extension regardless
	 ÀÄÁÄÁÄÁÄÄÄÄÄÄÄÄ 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
	- this function can be used to detect the existence of logical DOS
	  drives by creating a dummy filespec with a drive letter and colon
	  prepended.  If the drive is invalid, this function will return FF
	  in AL
: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
	- updates ~BIOS Data Area~ current date and date rollover flag
	  at location 40:70

: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 versions 3.3+ also update the ~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~

: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 decimal)
	BH = FF  indicates MS-DOS, only if OEM vendor chooses to identify
	   = 00  indicates PC-DOS
	BL:CX = 24 bit OEM serial number if BH is FF


	- 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
	- the OEM serial number is a rarity, though some older OEM DOS
	  versions implemented this feature
	- the OS/2 compatibility box returns 10.10 for OS/2 1.1, 10.20
	  for OS/2 1.2, etc...
	- when testing for version, a specific test can often cause your
	  code to not work in following versions of DOS.  It is often better
	  to test for a version number greater or equal to the minimum rather
	  than a specific version number where possible
	- see ~DOS Versions~
: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, this may also
	  indicate a Bernoulli box)
	- can be used to determine if a drive is a RAM disk; if the disk is
	  NOT removable and (DS:[BX+1] == 0), then the disk is a RAM disk
	  (see ~IOCTL,0~ bit number 0Bh to determine if the disk is removable)
:int 21,33
^INT 21,33 - Get/Set System Values (Ctl-Break/Boot Drive)


	AH = 33h
	AL = 00 to get Ctrl-Break checking flag
	   = 01 to set Ctrl-Break checking flag
	   = 02 to set extended Ctrl-Break checking
	   = 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 or AL=2)
	   = 01 Ctrl-Break checking ON	(AL=0 or AL=2)
	   = boot drive number (1-26, A: - Z:) (function 05)


	- retrieves DOS Ctrl-Break or extended Ctrl-Break setting which
	  determines if DOS will check for Ctrl-Break during INT 21 calls
:int 21,34:INDOS
^INT 21,34 - Get Address to DOS Critical Flag
^INDOS	(Undocumented DOS 2.0+)

	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 otherwise.
	- though this flag indicates whether a DOS interrupt is active, it
	  should not be used alone to determine DOS is safe for re-entry;
	  Here's the standard rule for safe DOS entry: if ~INT 28~ is active
	  or this flag and the critical error flag are clear then it is safe
	  to call DOS
	- this interrupt should be used only during TSR initialization;
	  the returned pointer should be used thereafter
	- this flag is cleared after 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
	  ~INT 21,5D~ in DOS 3.x+ can be used to locate the critical
	  error flag
: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, DOS 2.0+)


	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 may be accessed without prefix
	   = 3	set device prefix flag, device names must begin with \DEV\.
	DL = new switch character (AL=1)
	   = 00  \DEV\ must preceed device names (AL=3)
	   = 01  \DEV\ is not neccesary in device names (AL=3)

	on return:
	AL = FF  illegal subfunction code specified
	DL = current switch character (AL=0)
	   = device availability (AL=2, always FF with DOS 4.x+)


	- subfunctions 0 and 1 were formerly available as a CONFIG.SYS
	  command in DOS versions before 3.x;	also supportedin the OS/2
	  compatibility box
	- subfunctions 2 and 3 were available in DOS 2.x only;	they have
	  no effect in DOS 4.x+
	- /DEV/ prefix is valid in DOS 2.x by default, setting the flag makes
	  it mandatory.  DOS internal commands like DIR, TYPE and DEL do not
	  recognize filenames the are identical to device names regardless of
	  the setting of the AVAILDEV flag.
: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
: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:

	³7³6³5³4³3³2³1³0³  AL
	 ³ ³ ³ ³ ³ ÀÄÁÄÁÄÄÄÄ read/write/update access mode
	 ³ ³ ³ ³ ÀÄÄÄÄÄÄÄÄÄ reserved, always 0
	 ³ ÀÄÁÄÁÄÄÄÄÄÄÄÄÄÄ sharing mode (see below) (DOS 3.1+)
	 ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 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, a zero value truncates/extends
	     the file to the current file position
	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
	- this function can be used to truncate a file to the current
	  file position by writing zero bytes
: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
	- documented as not accepting wildcards in filename but actually
	  does in several DOS versions
: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
: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

	³5³4³3³2³1³0³  CX  valid file attributes
	 ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = read only
	 ³ ³ ³ ³ ÀÄÄÄÄÄ 1 = hidden
	 ³ ³ ³ ÀÄÄÄÄÄÄ 1 = system
	 ³ ÀÄÁÄÄÄÄÄÄÄ not used for this call
	 ÀÄÄÄÄÄÄÄÄÄÄ 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


%	For more information, see the following topics:

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


	³F³E³D³C³B³A-8³7³6³5-0³  DX  Block Device Information
	 ³ ³ ³ ³ ³  ³  ³ ³  ÀÄÄÄÄÄ drive number (0=A:,1=B:)
	 ³ ³ ³ ³ ³  ³  ³ ÀÄÄÄÄÄÄÄ 0 = file has been written
	 ³ ³ ³ ³ ³  ³  ÀÄÄÄÄÄÄÄÄ 0 = disk file; 1 = character device
	 ³ ³ ³ ³ ³  ÀÄÄÄÄÄÄÄÄÄÄ reserved, must be zero
	 ³ ³ ³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄ 1 = media not removable
	 ³ ³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄ 1 = network device (DOS 3.x+)
	 ³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 1 = reserved
	 ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 1 = don't update file time or date (DOS 4.x+)
	 ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 1 = file is remote (DOS 3.x+)

	³F³E³D³C³B³A-8³7³6³5³4³3³2³1³0³  DX  Character Device Information
	 ³ ³ ³ ³ ³  ³  ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = standard input device
	 ³ ³ ³ ³ ³  ³  ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = standard output device
	 ³ ³ ³ ³ ³  ³  ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = NUL device
	 ³ ³ ³ ³ ³  ³  ³ ³ ³ ³ ÀÄÄÄÄ 1 = clock device
	 ³ ³ ³ ³ ³  ³  ³ ³ ³ ÀÄÄÄÄ uses DOS ~INT 29~ for fast character output
	 ³ ³ ³ ³ ³  ³  ³ ³ ÀÄÄÄÄ 1 = binary mode, 0 = translated
	 ³ ³ ³ ³ ³  ³  ³ ÀÄÄÄÄ 0 = end of file on input
	 ³ ³ ³ ³ ³  ³  ÀÄÄÄÄ 1 = character device, 0 if disk file
	 ³ ³ ³ ³ ³  ÀÄÄÄÄÄ reserved
	 ³ ³ ³ ³ ÀÄÄÄÄÄÄ 1 = media not removable
	 ³ ³ ³ ÀÄÄÄÄÄÄ 1 = network device (DOS 3.x+)
	 ³ ³ ÀÄÄÄÄÄÄ reserved
	 ³ ÀÄÄÄÄÄÄ 1 = supports IOCTL, via functions 2 & 3
	 ÀÄÄÄÄÄÄ 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
	- BIT B of register DX can be used to determine if a drive is
	  removable.

: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

	³F³E³D³C³B³A³9³8³7³6³5³4³3³2³1³0³  Device Data Word
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = standard input device
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = standard output device
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = NUL device
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = clock device
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ reserved
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = binary mode, 0 = translated
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 0 = end of file on input
	 ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = character device
	 ÀÄÁÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄ 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  ~INT 21,49~,  ~INT 21,4A~
: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 wasn't allocated by the 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
	- this function is unreliable in a TSR once resident, since
	  COMMAND.COM and many other .COM files take all available memory
	  when they load
	- see  INT 21,4A
: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
	- PC-DOS version 2.1 and DOS 3.x will actually allocate the largest
	  available block if CF is set.  BX will equal the size allocated.
	- see also  ~INT 21,49~
: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
	   = 04  called by MSC spawn() when P_NOWAIT is specified
	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 = when AL=1, pointer to parameter block similar to:

%	Offset Size	       Description

	  00   word   when AL=1, segment of env. or zero if using parents env.
	       word   when AL=3, segment of load point for overlay
	  02   dword  when AL=1, pointer to cmd line at PSP 80h
	       word   when AL=3, relocation factor for EXE overlay
	  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
	- subfunction 4 returns with an error under DOS 4.x+
	- calls ~INT 21,55~

	- see also  ~INT 21,26~

: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, ~Ctrl-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 use ~INT 21,0~  or	 ~INT 20~  to exit.


	- see also  ~INT 27~   ~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)
	       byte    drive letter used in search (DOS 3.1-4.x, undocumented)
	  01   byte    drive letter used in search (undocumented)
	     11bytes   search name used (DOS 3.1-4.x, undocumented)
	  02 11bytes   search name used (undocumented)
	  0C   byte    attribute of search (DOS 3.1-4.x, undocumented)
	  0D   word    directory entry number (0 based, undocumented)
	  0F   word    starting cluster number of current directory; zero
		       for root directory  (DOS 3.2+, undocumented)
	       dword   pointer to DTA (DOS 2.x-3.1, undocumented)
	  11   word    reserved
	  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
	- character devices return a zero for size, time and date in DOS 2.x,
	  while DOS 3.0 returns a 40h attribute and current time and date.
	- multiple calls to this function with a character device will
	  result in unpredictable results
	- normal files are always included along with files that match the
	  requested attributes except when the LABEL attribute is requested.
	  DOS 2.x returns all normal files when label is specified but 3.x
	  doesn't.  It's up to the programmer to determine which actually
	  match the requested attributes.
	- bit 8 of CX (file attributes) indicates Novell Netware shareable
	- see	INT 21,1A

: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 21,1A~  ~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 a
	  program's PSP.  This is useful for TSR's to access their own
	  file handle table inside their PSP.
	- this function cannot be called while in an ~INT 28~ handler in
	  DOS 2.x unless the critical error flag is set or stack corruption
	  will occur
	- safe in DOS 3.x INT 28 handlers since they use a different stack
	  by default
	- available in OS/2 compatibility box
	- see  ~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~.
	- this function cannot be called while in an ~INT 28~ handler in
	  DOS 2.x unless the critical error flag is set or stack corruption
	  will occur
	- ~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
: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 3.1-3.3)
	 -10   word   sharing retry delay  (DOS 3.1-3.3)
	  -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 (~MCB~)
	  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   number of joined drives
	  35   word   pointer within IBMDOS code segment to list of special
		      program names
	  37   dword  pointer to resident IFS utility function
	  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 ~Bibliography~ references for Bernd Schemmer & "Undocumented DOS"
	- see   ~INDOS~  ~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 buffer to hold first Drive Parameter Table (~DPT~)


	returns:
	ES:BP = pointer to buffer containing the first Drive Parameter Table
		in chain


	- available since DOS 2.0+
	- translates BPB  into a DOS Disk Parameter Table
	- see  ~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
	SI = memory size value to place in ~PSP~ offset 02h (DOS 3+)

	returns nothing

	- 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
	- increments reference count in ~SFT~ for all inherited files
	- files flagged as not inheritable are marked as closed in the
	  new PSP
	- 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 unless invoked from via
	  ~INT 21,5D~ in which case error code 12h is returned
	- unpredictable result may occur if an opened file is renamed
	- see ~Bibliography~ reference to "Undocumented DOS"
: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+ undocumented)
	   = 03  ??? (DOS 4.0+ undocumented) 
	   = 04  ??? (DOS 4.0+ undocumented)
	BX = file handle
	CX = time to set (if setting)
	DX = date to set (if setting)
	ES:DI = pointer to buffer to contain results


	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:

	³F³E³D³C³B³A³9³8³7³6³5³4³3³2³1³0³  Time in CX
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÁÄÄÄÄ  two second incr (0-29)
	 ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄ  minutes 0-59)
	 ÀÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ  hours (0-29)

%	Date Encoding

	³F³E³D³C³B³A³9³8³7³6³5³4³3³2³1³0³  Date in DX
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÁÄÄÄÄ  day (1-31)
	 ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄ  month (1-12)
	 ÀÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ  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, see  ~DOS ERROR CODES~


	- 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
	  and uses the high part of the chosen block
	- any strategy value greater than 2 defaults to 2, but the last value
	  set, even if incorrect, is the value returned by the get strategy
: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
: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.x+)

%	See second reference below for more information about this interrupt
%	information presented here is incomplete

	AH = 5D
	AL = 00  server function call  (DOS 3.1+)
	   = 01  commit all files  (DOS 3.1+)
	   = 02  SHARE: close file by name  (DOS 3.1+)
	   = 03  SHARE: close all files for given computer  (DOS 3.1+)
	   = 04  SHARE: close all files for given process  (DOS 3.1+)
	   = 05  SHARE: get open file list entry  (DOS 3.1+)
	   = 06  get address of DOS swappable area into DS:SI  (DOS 3.0+)
	   = 07  get network redirected printer mode  (DOS 3.1+)
	   = 08  set network redirected printer mode  (DOS 3.1+)
	   = 09  flush network redirected printer output  (DOS 3.1+)
	   = 0A  set extended error information  (DOS 3.1+)
	   = 0B  get DOS swappable data areas  (DOS 4.x+)
	DS:DX = pointer to 18 byte DOS Parameter List (DPL, if 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 = (if AL was 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 ~bibliography~ references for "Undocumented DOS" and "DOS
	  Programmers Reference"

	- see	~INT 21,59~
:int 21,5e
^INT 21,5E  AL=0  Get Machine Name  (DOS 3.1+)

	AH = 5E
	AL = 00 get machine name
	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=01  Set Machine Name  (DOS 3.1+)

	AH = 5E
	AL = 01 set machine name
	CH = 00 undefine name
	   = any other value means to define name
	CL = name number
	DS:DX = pointer to 15 byte, blank padded ASCIIZ name string


	on return:
	AX = error code if CF set, (invalid function)


	- specifies the network machine name on a Microsoft network
	- unpredictable if called without file sharing loaded


^INT 21,5E  AL=02  Set Printer Setup  (DOS 3.1+)


	AH = 5E
	AL = 02 set printer setup
	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=03  Get Printer Setup  (DOS 3.1+)


	AH = 5E
	AL = 03 get printer setup
	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


	- 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=04  Set Printer Mode  (DOS 3.1+)


	AH = 5E
	AL = 04  set printer setup
	BX = redirection list index (see INT 21,5F AL=2)
	DX = printer mode to set (bit zero is set for binary mode and clear
	     for translated/text mode)


	on return:
	AX = error code if CF set


	- see INT 21,5F subfunction 2 for information on obtaining the
	  redirection list index
	- fails if file sharing is not loaded
	- issues ~INT 2F,11~  and  ~INT 2F,1F~


^INT 21,5E  AL=05  Get Printer Mode  (DOS 3.1+)


	AH = 5E
	AL = 05  set printer setup
	BX = redirection list index (see INT 21,5F AL=2)


	on return:
	AX = error code if CF set
	DX = printer mode where bit zero is set for binary mode and
	     clear for translated mode



	- see ~INT 21,5F~ subfunction 2 for information on obtaining the
	  redirection list index
	- fails if file sharing is not loaded
	- issues  ~INT 2F,11~  and  ~INT 2F,1F~
:int 21,5f
^INT 21,5F  AL=00  Get Redirection Mode  (DOS 3.1+)


	AH = 5F
	AL = 00
	BL = redirection type
	   = 03  printer
	   = 04  disk drive


	on return:
	AX = error code if CF is set
	BH = device redirection state
	   = 00  redirection off
	   = 01  redirection on


	- determines if disk or printer redirection is enabled
	- fails if file sharing is not loaded


^INT 21,5F  AL=01  Set Redirection Mode  (DOS 3.1+)


	AH = 5F
	AL = 01
	BH = device redirection state
	   = 00  turn redirection off
	   = 01  turn redirection on
	BL = redirection type
	   = 03  printer
	   = 04  disk drive


	on return:
	AX = error code if CF is set


	- enables or disables disk or printer redirection
	- local devices are used when redirection is off
	- fails if file sharing is not loaded


^INT 21,5F  AL=02  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=03  Redirect Device  (DOS 3.1+)

	AH = 5F
	AL = 03
	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=04  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 21,5F  AL=05  Get Redirection List Extended Entry (DOS 4.0+)

	AH = 5F
	AL = 05
	BX = redirection list index
	DS:SI = pointer to buffer to receive ASCIIZ source device name
	ES:DI = pointer to buffer to receive ASCIIZ network path

	on return
	AX = error code if CF set
	BH = device status flag (bit 0 clear if valid)
	BL = device type
	   = 03  printer device
	   = 04  disk device
	CX = stored user parameter value
	BP = NETBIOS local session number
	DS:SI = pointer to buffer containing ASCIIZ source device name
	ES:DI = pointer to buffer containing ASCIIZ network path


	- retrieves the status, type, source and target of a given redirection
	- fails if file sharing is not loaded


^INT 21,5F  AL=06  Get Redirection List (DOS 4.0+)


	AH = 5F
	AL = 06

	- no information is currently available for this subfunction
:int 21,60
^INT 21,60 - Get Fully Qualified File Name (Undocumented 3.x+)


	AH = 60h
	DS:SI = pointer to ASCIIZ string containing unqualified filename
	ES:DI = pointer to 128 byte buffer to contain fully qualified filename


	on return:
	ES:DI = address of fully qualified filename string
	AH = error code if CF set


	- undocumented, available in DOS 3.x+
	- does not check for file existence, simple provides a fully
	  qualified filename for the given filespec
	- this function ignores ASSIGN'ed, JOIN'ed, SUBST'ed and network
	  redirections and returns the true path name
	- returned string is in upper case and has forward slashes replaced
	  by back slashes;  filename always begins with "d:" or "\\" format
	- AL register is destroyed
	- supported by OS/2 1.1 compatibility box
: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 also  ~INT 21,50~
:int 21,63
^INT 21,63 - Get Lead Byte Table  (MSDOS 2.25 only)

%	See below for information on the Asian INT 21,63 specifications

	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  clear interim console flag (when AL=01)
	   = 01  set interim console flag (when AL=01)

	on return
	AX = error code if CF set
	DS:SI = far pointer to lead byte table (AL=00)
	DL = value of interim console flag (AL=02)

	- available only in MSDOS 2.25
	- provides multiple byte character support
	- function 00, returns the address of system table containing
	  legal lead byte ranges
	- function 01 & 02 set and get the interim console flag which
	  determines whether interim bytes are returned on some console
	  functions
	- all registers except CS:IP and SS:SP may be destroyed


^INT 21,63 - Get Lead Byte Table  (Asian DOS 3.2+)

	AH = 63h
	AL = 00  get address of Double Byte Character Set (DBCS) lead table
	   = 01  set Hongeul (Korean) input mode
	   = 02  get Hongeul (Korean) input mode
	DL = new keyboard input mode
	   = 00  return completely formed characters only
	   = 01  return partially formed characters also


	on return
	AL = 00 on success
	   = FF if function not supported
	DS:SI = pointer to DBCS table  (function 00)
	DL = current keyboard input mode (function 02)
	   = 00  only completely formed characters are accepted
	   = 01  partially formed characters are accepted


	- available only in Asian MSDOS 3.2+
	- provides Asian multiple byte character support
	- all registers except CS:IP and SS:SP may be destroyed
	- DOS 4.0 returns an empty list
: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 21,1~, ~INT 21,8~ and ~INT 21,A~
	     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
	- some other subfunctions are know to have existed since DOS 3.2 but
	  details on their functionality are incomplete
: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  get pointer to filename terminator table
	   = 06  get pointer to collating sequence
	   = 07  get segment of DCBS vector (DOS 4.x)
	   = 20  country dependant character capitalization (DOS 4+)
	   = 21  country dependant string capitalization (DOS 4+)
	   = 22  country dependant ASCIIZ string capitalization (DOS 4+)
	   = 23  determine if character represents country relative
		 Yes or No response (DOS 4+)
	   = A0  country dependant filename character capitalization (DOS 4+)
	   = A1  country dependant filename string capitalization (DOS 4+)
	   = A2  country dependant ASCIIZ filename capitalization (DOS 4+)
	BX = code page (-1 = current global code page, AL < 20h)
	CX = amount of data to return
	   = length of string (AL=21h, A1h)
	DX = country ID (-1 = current country, AL < 20h)
	DL = character to capitalize or test (AL=20h, 23h, A0h)
	DH = second character if double byte character (AL=23h)
	ES:DI = pointer to output buffer (AL < 20h, see tables below)
	DS:DX = pointer to string to capitalize (AL=21h, 22h, A1h, A2h)


	on return
	AX = error code if CF is set  (see ~DOS ERROR CODES~)
	   = 00  NO response if (AL was 23h)
	   = 01  YES response if (AL was 23h)
	   = 02  not a yes or no response (AL was 23h)
	CX = amount of data returned
	DL = capitalize character (AL=20)
	ES:DI pointer to returned table of the forms:


%	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 character translation table


%	Offset Size	Table for Function 5
	  00   byte   country Id = 05
	  01   dword  pointer to filename uppercase table


%	File Terminator Table for Function 5
	  00   word   table size
	  02  7bytes  unknown
	  09   byte   length of following data
	  0A  nbytes  list of filename termination characters, ex:
		      < > . " / \ [ ] : | + = ; ,

%	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


	- functions A0, A1, A2 are implemented in DOS 4.x but don't work
: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 (up to 64K) if an even number of handles is requested
	- only the first 20 files handles are copied to a child process
	  regardless of the max number of files
	- it is possible to allocate more than 255 file handles but it is
	  difficult to use more than 255

	- 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 (~BPB~, 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:
	CF = set on error
	   AX = error code if CF set
	      = 01  network drive not supported
	      = 05  no extended BPB found on disk
	CF = clear if successful and value in AX is destroyed
	   AL = 00  buffer filled from Extended BPB on disk
	      = 01  disk Extended BPB updated from buffer
	DS:DX = pointer to returned data, when AL = 0


	- copies data from Extended BIOS Parameter Block to buffer
	- no critical error is generated on error
	- does not work on network drives (returns 01)
	- returned buffer (after offset 2) is similar to offsets 27 through
	  3D of the Extended BPB found in the boot record

	- see  ~INT 21,59~
: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:

	³F³E³D³C³B³A³9³8³7³6³5³4³3³2³1³0³  BX  (Open Mode)
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÄÄÄ read/write access mode
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄÄÄ reserve (must be 0)
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÄÄÄÄÄÄÄ sharing mode
	 ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄ 1 = private, 0 = inheritable
	 ³ ³ ³ ÀÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄ reserved
	 ³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 0 = call INT 24, 1 = ignore INT 24
	 ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 0 = normal write, 1 = flush each write
	 ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 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:

	³F³E³D³C³B³A³9³8³7³6³5³4³3³2³1³0³  DX  (Function Control)
	 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÄÄÄ file existence behavior
	 ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄ creation behavior
	 ÀÄÁÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 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~.
: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
: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 also   ~INT 9~
: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

		  ³5³4³3³2³1³0³  AH
		   ³ ³ ³ ³ ³ ÀÄÄÄÄ read = 0, write = 1
		   ³ ³ ³ ÀÄÁÄÄÄÄÄ 00=DOS, 01=FAT, 10=DIR, 11=data area
		   ³ ³ ÀÄÄÄÄÄÄÄÄ 0=FAIL not allowed, 1=FAIL allowed
		   ³ ÀÄÄÄÄÄÄÄÄÄ 0=RETRY not allowed, 1=RETRY allowed
		   ÀÄÄÄÄÄÄÄÄÄÄ 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 21,0~ through ~INT 21,C~ 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 critical 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 but the last 3 words from the stack (FLAGS,
	  CS, IP) and issue an ~IRET~
	- 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
	- supported by OS/2 compatibility box
	- default behavior is to simply perform an ~IRET~
	- any DOS functions above 0Ch may be called while in this handler
	- ~INT 21,3F~ and ~INT 21,40~ may not use a handle that refers to
	  CON while in this handler
	- see also  ~INDOS~
:int 29
^INT 29 - DOS Fast Character I/O  (Undocumented 2.x+)


	AL = character to write


	returns nothing ???


	- used by DOS device drivers to output data to the screen if
	  bit 4 of the device attribute word is set
	- similar to ~INT 21,2~ and ~INT 21,9~ but much faster
	- simply calls the BIOS ~INT 10,E~ in DOS versions 2.x and 3.x
	- advances the cursor after character output
:int 2a
^INT 2A - DOS Network Critical Section and NETBIOS

%	For more information see the following topics:

	 ~INT 2A,0~  Network installation query
	 ~INT 2A,1~  Execute NETBIOS request with no error retry
	 INT 2A,2  Set network printer mode (not listed)
	 ~INT 2A,3~  Check if direct I/O allowed
	 ~INT 2A,4~  Execute NETBIOS request
	 ~INT 2A,5~  Get network resource information
	 ~INT 2A,6~  Network print stream control
	~INT 2A,80~  Begin DOS critical section
	~INT 2A,81~  End DOS critical section
	~INT 2A,82~  End DOS critical sections 0 through 7
	~INT 2A,84~  Keyboard busy loop
	~INT 2A,87~  Critical section

	- functions requests are supplied in AH
:int 2a,0
^INT 2A,0 - Network Installation Query


	AH = 00
	

	on return:
	AH = zero if not installed
	   = nonzero if installed


	- used to detemine if a Microsoft compatible network is present
:int 2a,1
^INT 2A,1 - Execute NETBIOS Request With No Error Retry


	AH = 01
	ES:BX = pointer to Network Control Block
	

	on return:
	AL = NETBIOS error code
	AH = zero if success
	   = nonzero if error


	- similar to INT 5C
:int 2a,3
^INT 2A,3 - Check if Direct I/O Allowed


	AH = 03
	DS:SI = pointer to ASCIIZ disk device name or pathname (including ":")
	
	
	on return:
	CF = set if disk access is NOT allowed
	   = clear if disk access is allowed


	- do not use ~INT 13~, ~INT 25~ or ~INT 26~ if this function returns
	  with the CF set
	- see  ~INT 5F,2~
:int 2a,4
^INT 2A,4 - Execute NETBIOS Request


	AH = 04
	AL = 00  allow retry
	   = 01  no retry allowed
	ES:BX = pointer to Network Control Block (NCB)
	
	
	on return:
	AX = 00 if successful
	AH = 01 if error
	AL = error code if AH = 01


	- invokes NETBIOS handler and allows retry of operation if specified
:int 2a,5
^INT 2A,5 - Get Network Resource Information


	AX = 0500
	
	
	on return:
	AX = destroyed
	BX = number of available network names
	CX = number of available NCB commands
	DX = number of available sessions


	- returns information on the number of available network resources
:int 2a,6
^INT 2A,6 - Network Print Stream Control


	AH = 06
	AL = 01 set concatenation mode where all printer output is placed
		in one job
	   = 02 set truncation mode where each printer open and printer
		close starts a new job
	   = 03 flush printer output then start a new print job (similar to
		pressing Ctrl-Alt-Kp-* )
	
	
	on return:
	AX = error code if CF set


	- allows control of network printers
:int 2a,80
^INT 2A,80 - Begin DOS Critical Section

	AH = 80h
	AL = critical section identifier (00-0F)
	   = 01  DOS kernel, SHARE.EXE and network data structure integrity
	   = 02  DOS kernel, device driver exclusivity
	   = 05  IFSFUNC (Installable File System, IFS, DOS 4.0+)
	   = 06  IFSFUNC (Installable File System, IFS, DOS 4.0+)
	   = 08  ASSIGN.COM
	
	returns nothing


	- indicates that the region of code being entered should not be
	  interrupted and identifies the critical region
	- this function is not normally called by user applications but is
	  often hooked to monitor if DOS is in a critical section
	- this information is necessary to reenter DOS using the swappable
	  data area returned by ~INT 21,5D~ subfunction 0B
	- see  ~Bibliography~ reference to "Undocumented DOS"
:int 2a,81
^INT 2A,81 - End DOS Critical Section

	AH = 81h
	AL = critical section identifier (00-0F)
	   = 01  DOS kernel, SHARE.EXE and network data structure integrity
	   = 02  DOS kernel, device driver exclusivity
	   = 05  IFSFUNC (Installable File System, IFS, DOS 4.0+)
	   = 06  IFSFUNC (Installable File System, IFS, DOS 4.0+)
	   = 08  ASSIGN.COM


	returns nothing


	- indicates that a critical code section is being exited
	- this function is usually hooked rather then called directly from a
	  user application
	- see  ~Bibliography" reference to "Undocumented DOS"
:int 2a,82
^INT 2A,82 - End DOS Critical Sections 0 thru 7


	AH = 82h


	returns nothing


	- the DOS function dispatcher calls this function during DOS
	  function 00, functions above 0C (excluding function 59h) and
	  during process termination
	- this function is usually hooked rather then called directly from
	  a user application
	- see  ~Bibliography~ reference to "Undocumented DOS"
:int 2a,84
^INT 2A,84 - Keyboard Busy Loop


	AH = 84h


	returns nothing


	- allows other processes to continue while waiting for keyboard
	  input, similar to ~INT 28~
	- see  BIBLIO reference to "Undocumented DOS"
:int 2a,87
^INT 2A,87 - Critical Section


	AH = 87h
	AL = 00  start critical section
	   = 01  end critical section


	returns nothing


	- specifies the start or end of a critical section
	- called by PRINT.COM
	- see  ~Bibliography~ reference to "Undocumented DOS"
:int 2e
^INT 2E - Execute Command Using Base Level Command Interpreter
^(Undocumented DOS 2.0+)

	DS:SI = pointer to command string to be executed

	returns nothing ???

	- causes the base level COMMAND.COM to execute a command as if it
	  were typed from the keyboard
	- the transient portion of COMMAND.COM must be loaded if not resident
	- first byte of the string contains the string length, inclusive
	- command string must be terminated with a CR
	- all registers including SS & SP are destroyed;  SS & SP should be
	  preserved in your own code segment
	- 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
:int 2f:multiplex interrupt
^INT 2F - DOS Multiplex Interrupt

%	For more information see the following topics:

					     ÚÄÄÄÄÄÄ ERROR CODES ÄÄÄÄ
	~INT 2F,0~  Get installed state	     ³ 01    Invalid function
	~INT 2F,1~  Submit file		     ³ 02    File not found
	~INT 2F,2~  Cancel file		     ³ 03    Path not found
	~INT 2F,3~  Cancel all files	     ³ 04    Too many files
	~INT 2F,4~  Pause / return status      ³ 05    Access denied
	~INT 2F,5~  End of status  	     ³ 08    Queue full
	~INT 2F,8~  DRIVER.SYS support	     ³ 09    Busy
	~INT 2F,2E~ Error Translation Tables   ³ 0C    Name too long
					     ³ 0F    Invalid drive

 	- function request is specified in AL or AH
	- see  ~INT 2F,0~  for installation checks
	- INT 2F uses AL to specify most documented functions but occasionally
	  uses AH also.  This can be quite confusing so INT 2F functions using
	  AH are not currently listed if the conflict but will be added at a
	  later time.
:int 2f,0
^INT 2F,0 - DOS Multiplex Interrupt - Get Installed State

	AL = 00
	AH = 00  DOS 2.x PRINT.COM (undocumented, see note below)
	     01  PRINT	(undocumented behavior also, see note below)
	     05  Critical error handler (undocumented DOS 3.0+)
	     06  ASSIGN  (see note)
	     08  DRIVER.SYS (undocumented DOS 3.2+)
	     10  SHARE
	     11  Redirector/IFS is resident
	     12  MultiDOS is resident
	     13  Swap 13h and 19h
	     14  NLSFUNC
	     15  GRAPHICS.COM (see note below)
		 MS CD-ROM extension (MSCDEX) (see note below)
	     16  Windows 386
	     17  DOS shell
	     19  SHELLB.COM (DOS 4.0 only)
	     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 installable command extension (DOS 3.3+)
	     B0  GRAFTABL.COM (DOS 3.3+)
	     B4  IBM 3270 emulation
	     B7  APPEND  (DOS 3.3+)
	     B8  LAN existence
	     B9  LAN RECEIVER.COM
	     BF  LAN 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
	- AH = 00 and 01 are used by DOS 2.x PRINT.COM and is not a check
	  for installed state, see BIBLIO reference to "Undocumented DOS"
	- ASSIGN returns non-zero if installed
	- installation checks with AH=15 do not follow the standard format;
	- see  ~Bibliography~ reference to "Undocumented DOS"
: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
	     06  get pointer to ASSIGN drive translation table (undoc DOS 3+)
	     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
	DS:DI
	
	on return:
	ES = segment of ASSIGN work area and assignment table (AH=6 only)

: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,6
^INT 2F,6 - PRINT.COM Check for Error on Output Device (Undocumented)


	AL = 06
	AH = 01


	on return:
	AX = error code if CF set
	   = 00 on success
	DS:SI = device driver header if CF set


	- checks the output device for an error condition
	- undocumented, available since DOS 3.3+
:int 2f,8
^INT 2F,8 - DRIVER.SYS Support	(Undocumented DOS 3.2+)


	AH = 08
	AL = 00  installation check
	   = 01  add new block device
	   = 02  execute device driver request
	   = 03  get drive data table list (DOS 4.0+)
	DS:DI = pointer to drive data table  (AL=01)
	ES:BX = pointer to device driver request header (AL=02)


	on return:
	AL = 00  not installed, ok to install (AL=00)
	   = 01  not installed, do NOT install (AL=00)
	   = FF  installed (AL=00)
	ES:BX = updated device request header (AL=02)

	- function 01 scans DOS's drive data tables and appends the new
	  data table to to the chain.  All tables referencing the same
	  physical drive are updated

: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 2f,80
^INT 2F,80 - PRINT.COM Time Slice Allotment  (Undocumented DOS 3.1+)

	AL = 80h
	AH = 00
	
	
	returns nothing


	- DOS PRINT.COM is given a time slice
:int 33:mouse interrupt:mouse services
^INT 33 - Mouse Function Calls

%	For more information see the following topics:

	~INT 33,0~   Mouse Reset/Get Mouse Installed Flag
	~INT 33,1~   Show Mouse Cursor
	~INT 33,2~   Hide Mouse Cursor
	~INT 33,3~   Get Mouse Position and Button Status
	~INT 33,4~   Set Mouse Cursor Position
	~INT 33,5~   Get Mouse Button Press Information
	~INT 33,6~   Get Mouse Button Release Information
	~INT 33,7~   Set Mouse Horizontal Min/Max Position
	~INT 33,8~   Set Mouse Vertical Min/Max Position
	~INT 33,9~   Set Mouse Graphics Cursor
	~INT 33,A~   Set Mouse Text Cursor
	~INT 33,B~   Read Mouse Motion Counters
	~INT 33,C~   Set Mouse User Defined Subroutine and Input Mask
	~INT 33,D~   Mouse Light Pen Emulation On
	~INT 33,E~   Mouse Light Pen Emulation Off
	~INT 33,F~   Set Mouse Mickey Pixel Ratio
	~INT 33,10~  Mouse Conditional OFF
	~INT 33,13~  Set Mouse Double Speed Threshold
	~INT 33,14~  Swap interrupt subroutines
	~INT 33,15~  Get mouse driver state and memory requirements
	~INT 33,16~  Save mouse driver state
	~INT 33,17~  Restore mouse driver state
	~INT 33,18~  Set alternate subroutine call mask and address
	~INT 33,19~  Get user alternate interrupt address
	~INT 33,1A~  Set mouse sensitivity
	~INT 33,1B~  Get mouse sensitivity
	~INT 33,1C~  Set mouse interrupt rate (InPort only)
	~INT 33,1D~  Set mouse CRT page
	~INT 33,1E~  Get mouse CRT page
	~INT 33,1F~  Disable mouse driver
	~INT 33,20~  Enable mouse driver
	~INT 33,21~  Reset mouse software
	~INT 33,22~  Set language for messages
	~INT 33,23~  Get language number
	~INT 33,24~  Get driver version, mouse type & ~IRQ~ number

	- function is specified in AX
	- 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
	~INT 33,0~   Mouse Reset/Get Mouse Installed Flag
	~INT 33,15~  Get Mouse Driver State and Memory Requirements
	~INT 33,16~  Save Mouse Driver State
	~INT 33,17~  Restore Mouse Driver State
	~INT 33,1C~  Set Mouse Interrupt Rate (InPort only)
	~INT 33,1F~  Disable Mouse Driver
	~INT 33,20~  Enable Mouse Driver
	~INT 33,21~  Reset Mouse Software
	~INT 33,24~  Get Driver Version, Mouse Type & IRQ Number

%	Mouse Cursor Control Functions
	~INT 33,1~   Show Mouse Cursor
	~INT 33,2~   Hide Mouse Cursor
	~INT 33,4~   Set Mouse Cursor Position
	~INT 33,7~   Set Mouse Horizontal Min/Max Position
	~INT 33,8~   Set Mouse Vertical Min/Max Position
	~INT 33,9~   Set Mouse Graphics Cursor
	~INT 33,A~   Set Mouse Text Cursor
	~INT 33,F~   Set Mouse Mickey Pixel Ratio
	~INT 33,10~  Mouse Conditional OFF
	~INT 33,13~  Set Mouse Double Speed Threshold
	~INT 33,1A~  Set Mouse Sensitivity
	~INT 33,1B~  Get Mouse Sensitivity

%	Mouse Button and Position Feedback Functions
	~INT 33,3~   Get Mouse Position and Button Status
	~INT 33,5~   Get Mouse Button Press Information
	~INT 33,6~   Get Mouse Button Release Information
	~INT 33,B~   Read Mouse Motion Counters

%	Video Control and Feedback Functions
	~INT 33,1D~  Set Mouse CRT Page
	~INT 33,1E~  Get Mouse CRT Page

%	Mouse Interrupt Setup Functions
	~INT 33,C~   Set Mouse User Defined Subroutine and Input Mask
	~INT 33,14~  Swap Interrupt Subroutines

%	Alternate Mouse Interrupt Setup Functions
	~INT 33,18~  Set Alternate Subroutine Call Mask and Address
	~INT 33,19~  Get User Alternate Interrupt Address

%	Light Pen Emulation Functions
	~INT 33,D~   Mouse Light Pen Emulation On
	~INT 33,E~   Mouse Light Pen Emulation Off

%	International Language Support Functions
	~INT 33,22~  Set Language for Messages
	~INT 33,23~  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:

		³F-8³7³6³5³4³3³2³1³0³  Button Status
		  ³  ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ left button (1 = pressed)
		  ³  ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ right button (1 = pressed)
		  ÀÄÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄ 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:

		³F-8³7³6³5³4³3³2³1³0³  Button Status
		  ³  ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ left button (1 = pressed)
		  ³  ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ right button (1 = pressed)
		  ÀÄÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄ 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

		³F-8³7³6³5³4³3³2³1³0³  Button status
		  ³  ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ left button (1 = pressed)
		  ³  ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ right button (1 = pressed)
		  ÀÄÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄ 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:

	   ³F-5³4³3³2³1³0³ user interrupt mask in CX
	     ³	³ ³ ³ ³ ÀÄÄÄ cursor position changed
	     ³	³ ³ ³ ÀÄÄÄÄ left button pressed
	     ³	³ ³ ÀÄÄÄÄÄ left button released
	     ³	³ ÀÄÄÄÄÄÄ right button pressed
	     ³	ÀÄÄÄÄÄÄÄ right button released
	     ÀÄÄÄÄÄÄÄÄÄ 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:

	     ³F-2³1³0³
	       ³  ³ ÀÄÄÄ left button (1 = pressed)
	       ³  ÀÄÄÄÄ right button (1 = pressed)
	       ÀÄÄÄÄÄÄ 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:

		³F-8³7³6³5³4³3³2³1³0³ user interrupt mask in CX
		  ³  ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ cursor position changed
		  ³  ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ left button pressed
		  ³  ³ ³ ³ ³ ³ ÀÄÄÄÄÄ left button released
		  ³  ³ ³ ³ ³ ÀÄÄÄÄÄÄ right button pressed
		  ³  ³ ³ ³ ÀÄÄÄÄÄÄÄ right button released
		  ÀÄÄÁÄÁÄÁÄÄÄÄÄÄÄÄ 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:

	     ³F-2³1³0³
	       ³  ³ ÀÄÄÄ left button (1 = pressed)
	       ³  ÀÄÄÄÄ right button (1 = pressed)
	       ÀÄÄÄÄÄÄ 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:

		³F-8³7³6³5³4³3³2³1³0³ user interrupt mask in CX
		  ³  ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ alt key pressed during event
		  ³  ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ ctrl key pressed during event
		  ³  ³ ³ ³ ³ ³ ÀÄÄÄÄÄ shift key pressed during event
		  ³  ³ ³ ³ ³ ÀÄÄÄÄÄÄ right button up event
		  ³  ³ ³ ³ ÀÄÄÄÄÄÄÄ right button down event
		  ³  ³ ³ ÀÄÄÄÄÄÄÄÄ left button up event
		  ³  ³ ÀÄÄÄÄÄÄÄÄÄ left button down event
		  ³  ÀÄÄÄÄÄÄÄÄÄÄ cursor moved
		  ÀÄÄÄÄÄÄÄÄÄÄÄÄ 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:

	     ³F-2³1³0³
	       ³  ³ ÀÄÄÄ left button (1 = pressed)
	       ³  ÀÄÄÄÄ right button (1 = pressed)
	       ÀÄÄÄÄÄÄ 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

		³F-8³7³6³5³4³3³2³1³0³ user interrupt mask in CX
		  ³  ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ alt key pressed during event
		  ³  ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ ctrl key pressed during event
		  ³  ³ ³ ³ ³ ³ ÀÄÄÄÄÄ shift key pressed during event
		  ³  ³ ³ ³ ³ ÀÄÄÄÄÄÄ right button up event
		  ³  ³ ³ ³ ÀÄÄÄÄÄÄÄ right button down event
		  ³  ³ ³ ÀÄÄÄÄÄÄÄÄ left button up event
		  ³  ³ ÀÄÄÄÄÄÄÄÄÄ left button down event
		  ³  ÀÄÄÄÄÄÄÄÄÄÄ cursor moved
		  ÀÄÄÄÄÄÄÄÄÄÄÄÄ 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  (ó 100)
	CX = vertical coordinates per pixel  (ó 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~
:int 33,1b
^INT 33,1B - Get Mouse Sensitivity


	AX = 1B


	on return:
	BX = horizontal coordinates per pixel  (ó 100)
	CX = vertical coordinates per pixel  (ó 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

%	For more information, see the following topics:

	~INT 67,40~  Get EMM Status
	~INT 67,41~  Get Page Frame Base Address
	~INT 67,42~  Get Page Counts
	~INT 67,43~  Get Handle and Allocate Pages
	~INT 67,44~  Map Logical Page Into Physical Page Window
	~INT 67,45~  Release Handle and Memory Pages
	~INT 67,46~  Get EMM Version
	~INT 67,47~  Save Page Map Context
	~INT 67,48~  Restore Page Map Context
	~INT 67,49~  Get I/O Port Addresses
	~INT 67,4A~  Get Logical to Physical Page Mapping
	~INT 67,4B~  Get Handle Count
	~INT 67,4C~  Get Page Count for Handle
	~INT 67,4D~  Get Page Count for All Handles
	~INT 67,4E~  Get/Set Page Map Context
	~INT 67,4F~  Get/Set Partial Page Map
	~INT 67,50~  Map/Unmap Multiple Handle Pages
	~INT 67,51~  Reallocate Pages
	~INT 67,52~  Get/Set Handle Attributes
	~INT 67,53~  Get/Set Handle Name
	~INT 67,54~  Get Handle Directory
	~INT 67,55~  Alter Page Map and Jump
	~INT 67,56~  Alter Page Map and Call
	~INT 67,57~  Move/Exchange Memory Region
	~INT 67,58~  Get Mappable Physical Address Array
	~INT 67,59~  Get Expanded Memory Hardware Information
	~INT 67,5A~  Allocate Standard/Raw Pages
	~INT 67,5B~  Alternate Map Register Set DMA Registers
	~INT 67,5C~  Prepare Expanded Memory for Warm Boot
	~INT 67,5D~  Enable/Disable OS Functions
	~INT 67,60~  Get Physical Window Array

	- function number is specified in AH
	- 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 ó 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 ó 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,PS/2)


	- called 1024 times per second for periodic and alarm functions
	- decrements a DWORD counter by 976æ 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 PS/2


	- see	~INT 15,83~   ~INT 15,86~