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	Appendix B - DOS 10H, 21H, and 33H Interrupt Parameters
	Visual C++ 6: The Complete Reference
	Chris H. Pappas and William H. Murray, III

Copyright 1998 The McGraw-Hill Companies

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	Appendix B: DOS 10H, 21H, and 33H Interrupt Parameters

	Overview

	This appendix contains the most popular DOS, BIOS, and Mouse interrupts and parameters.

	Screen Control with BIOS-Type 10H Interrupts

	Syntax: INT 10H (when the following parameters are set to the required values).

	Interface Control of the CRT

	AH Value

Function

Input

Output

	AH = 0

Set the mode of display

AL = 0

40 25 color text

AL = 1

40 25 color text

AL = 2

80 25 color text

AL = 3

40 25 color text

AL = 4

320 200 4-color graphics

AL = 5

320 420 4-color graphics

AL = 6

640 200 2-color graphics

AL = 7

80 25 monochrome text

AL = 13

320 200 16-color graphics

AL = 14

640 200 16-color graphics

AL = 15

640 350 monochrome graphics

AL = 16

640 350 16-color graphics

AL = 17

640 480 2-color graphics

AL = 18

640 480 16-color graphics

AL = 19

320 200 256-color graphics

	AH = 1

Set cursor type

CH =

Bits 4–0 start of line for cursor

CL =

Bits 4–0 end of line for cursor

	AH = 2

Set cursor position

DH =

Row

DL =

Column

BH =

Page number of display (0 for graphics)

	AH = 3

Read cursor position

DH = row

DL = column

CH = cursor mode

CL = cursor mode

BH = page number of display

	AH = 4

Get light pen position

AH = 0, switch not down/triggered

AH = 1, valid answers as follows:

DH = row

DL = column

CH = graph line     (0 to 99)

BX = graph column

(0 to 319/639)

	AH = 5

Set active display page

AL =

New page value

(0 to 7) modes 0 and 1

(0 to 3) modes 2 and 3

	AH = 6

Scroll active page up

AL =

Number of lines, 0 for entire screen

CH =

Row, upper-left corner

CL =

Column upper-left corner

DH =

Row, lower-right corner

DL =

Column, lower-right corner

BH =

Attribute to be used

	AH = 7

Scroll active page down

AL =

Number of lines, 0 for entire screen

CH =

Row, upper-left corner

CL =

Column, upper-left corner

DH =

Row, lower-right corner

DL =

Column, lower-right corner

BH =

Attribute to be used

	Handling Characters

	AH Value

Function

Input

Output

	AH = 8

Read attribute/ character at cursor position

BH = AL = AH =

Display page Character read Attribute of character

	AH = 9

Write attribute/ character at cursor position

BH = CX = AL = BL =

Display page Count of characters to write Character to write Attribute of character

	AH = 10

Write character at cursor position

BH = CX = AL =

Display page Count of characters to write Character to write

	Graphics Interface

	AH Value

Function

Input

Output

	AH = 11

Select color palette

BH =

Palette ID (0 to 127)

BL =

Color for above ID

0—background (0 to 15)

1—palette

0—green(1), red(2), yellow(3)

1—cyan(1), magenta(2),     white(3)

	AH = 12

Draw dot on screen

DX =

Row (0 to 199)

CX =

Column (0 to 319/639)

AL =

Color of dot

	AH = 13

Read dot information

DX =

Row (0 to 199)

CX =

Column (0 to 319/639)

AL =

Value of dot

	ASCII Teletype Output

	AH Value

Function

Input

Output

	AH = 14

Write to active page

AL =

Character to write

BL =

Foreground color

	AH = 15

Get video state

AL =

Current mode

AH =

Number of screen columns

BH =

Current display page

	AH = 16

(Reserved)

	AH = 17

(Reserved)

	AH = 18

(Reserved)

	AH = 19

Write string

ES:BP =

Point to string

CX =

Length of string

DX =

Cursor position for start

BH =

Page number

AL = 0

BL = attribute (char, char, char,...char) cursor not moved

AL = 1

BL = attribute (char, char, char,...char) cursor is moved

AL = 2

(char, attr, char, attr...) cursor not moved

AL = 3

(char, attr, char, attr...) cursor is moved

	AH = 1A

R/W display combination code

	AH = 1B

Return functionality state information

	AH = 1C

Save/restore video state

	Specifications and Requirements for the DOS 21H Interrupt

	Syntax: INT 21H (when the following parameters are set to the required values).

	AH Value

Function

Input

Output

	AH = 0

End of program

(similar to INT 20H)

	AH = 1

Wait and display keyboard character with CTRL-BREAK check

AL = character entered

	AH = 2

Display character with CTRL-BREAK check

DL =

Character to display

	AH = 3

Asynchronous character input

AL = character entered

	AH = 4

Asynchronous character output

DL =

Character to send

	AH = 5

Character to write

DL =

Character to write

	AH = 6

Input keyboard character

DL =

0FFH if character entered, 0 if none

	AH = 7

Wait for keyboard character (no display)

AL = character entered

	AH = 8

Wait for keyboard character (no display— CTRL-BREAK check)

AL = character entered

	AH = 9

String displayed

DS:DX

Address of string; must end with $ sentinel

	AH = A

Keyboard string to buffer

DS:DX =

Address of buffer. First byte = size, second = number of characters read

	AH = B

Input keyboard status

AL–no character       = 0FFH       character = 0

	AH = C

Clear keyboard buffer and call function

AL =

1,6,7,8,0,A (function #)

	AH = D

Reset default disk drive

None

None

	AH = E

Select default disk drive

Al = number of drives DL–0 = A drive        1 = B drive, etc.

	AH = F

Open file with unopened FCB

DS:DX =

Location AL = 0FFH if not found AL = 0H if found

	AH = 10

Close file with FCB

DS:DX =

Location (same as AH = OFH)

	AH = 11

Search directory for match of unopened FCB

DS:DX =

AL = 0FFH if not found 00000AL = 0H if found Location DTA contains directory entry

	AH = 12

Search (after AH = 11) for other files that match wildcard specifications

(Same as AH = 11H)

	AH = 13

Delete file named by FCB

DS:DX =

Location (same as AH = 11H)

	AH = 14

Sequential read of open file. Number of bytes in FCB (record size)

DS:DX =

Location AL = 0 transfer OK AL = 1 end of file AL = 2 overrun DTA segment AL = 3 EOF/partial read

	AH = 15

Sequential write of open file. Transfer from DTA to file, with FCB update of current record

DS:DX =

Location AL = 0 transfer OK AL = 1 disk full/ROF AL = 2 overrrun DTA segment

	AH = 16

Create file (length set to zero)

DS:DX =

Location (same as AH = 11H)

	AH = 17

Rename file

DS:DX

Location AL = 0 rename OK AL = 0FFH no match found

	AH = 18

(DOS internal use)

	AH = 19

Drive code (default)

AL–0 = A drive       1 = B drive, etc.

	AH = 1A

Set Data Transfer Add

DS:DX =

Points to location

	AH = 1B

File Allocation Table

DS:DX =

Address of FAT DX = number of units AL = record/alloc. unit CX = sector size (same as AH = 1B)

	AH = 1C

Disk drive FAT information

DL =

Drive number: 0 = default, 1 = A, 2 = B

	AH = 1D

(DOS internal use)

	AH = 1E

(DOS internal use)

	AH = 1F

(DOS internal use)

	AH = 20

(DOS internal use)

	AH = 21

Random read file

DS:DX =

Location of FCB (same as AH = 14H)

	AH = 22

Random write file

DS:DX =

(same as AH = 21H)

	AH = 23

Set file size

DS:DX =

Location of FCB AL = 0 if set AL = 0FFH if not set

	AH = 24

Random record size

DS:DX =

Location of FCB

	AH = 25

Set interrupt vector (change address)

DS:DX = AL =

Address of vector table Interrupt number

	AH = 26

Create program segment

DX =

Segment number

	AH = 27

Random block read

DS:DX =

Address of FCB AL–0 read OK       1 EOF       2 wrap around       3 partial record

	AH = 28

Random block write

DS:DX =

Address of FCB AL–0 write OK       1 lack of space

	AH = 29

Parse file name

DS:SI = DS:DI =

Point to command line Memory location for FCB AL = bits to set options

	AH = 2A

Read date

CX = year (80 to 99) DH = month (1 to 12) DL = day (1 to 31)

	AH = 2B

Set date

CX and DX (same as previous) AL–0 if valid 0FF if not valid

	AH = 2C

Read time

CH = hours (0 to 23) CL = minutes (0 to 59)

	AH = 2D

Set time

CX and DX (same as previous) AL–0 if valid 0FF if not valid

	AH = 2E

Set verify state

DL = AL =

0 0 = verify off 1 = verify on

	AH = 2F

Get DTA

ES:BX =

Get DTA into ES

	AH = 30

Get DOS version

AL = version number AH = sub number

	AH = 31

Terminate and remain resident

AL = exit code DX = memory size in paragraphs

	AH = 32

(DOS internal use)

	AH = 33

CTRL-BREAK check

AL = AL =

0 = request state 1 = set the state DL = 0 for off DL = 1 for on

	AH = 34

(DOS internal use)

	AH = 35

Read interrupt address

AL =

Interrupt number ES:BX point to vector address

	AH = 36

Disk space available

DL =

Drive (0 = default, 1 = A, 2 = B, etc.) AX = sectors/cluster (FFFF if invalid) BX = number of free clusters CX = bytes per sector DX = total number of clusters

	AH = 37

(DOS internal use)

	AH = 38

Country-dependent information (32-byte block)

DS:DX =

Location of memory Date/time Currency symbol Thousands separator Decimal separator

	AH = 39

Make directory

DS:DX =

Address of string for directory

	AH = 3A

Remove directory

DS:DX =

Address of string for directory

	AH = 3B

Change directory

DS:DX =

Address of string for new directory

	AH = 3C

Create a file

DS:DX = CX =

Address of string for file AX = file handle File attribute

	AH = 3D

Open a file

DS:DX = AL =

Address of string for file 0 = open for reading 1 = open for writing 2 = open for both AX returns file handle

	AH = 3E

Close a file handle

BX =

File handle

	AH =3F

Read a file or device

BX = CX = DS:DX =

File handle Number of bytes to read Address of buffer AX = number of bytes read

	AH = 40

Write a file or device

BX = CX = DS:DX =

File handle Number of bytes to read Address of buffer AX = number of bytes written

	AH = 41

Delete a file

DS:DX =

Address of file string

	AH = 42

Move file pointer

BX = AL = CX:DX DX:AX

File handle Pointer’s starting location Number of bytes Current file pointer

	AH = 43

Set file attribute

AL = 1 CX = DS:DX =

Attribute Address of file string

	AH = 45

Duplicate file handle

BX

File handle AX = returned file handle

	AH = 46

Force duplicate file handle

BX

File handle CX = second file handle

	AH = 47

Current directory

DL = DS:SI =

Drive number (0 = default, 1 = A drive, 2 = B drive) Buffer address DS:SI returns address of string

	AH = 48

Allocate memory

BX

Number of paragraphs AX = allocated blocks

	AH = 49

Free allocated memory

ES

Segment of returned block

	AH = 4A

Set block

ES BX

Segment block New block size

	AH = 4B

Load/execute program

DS:DX

Location of ASCIIZ string (drive/path/filename) AL–0 = load and execute       3 = load/no execute

	AH = 4C

Terminate (exit)

AL

Binary return code (all files closed)

	AH = 4D

Retrieve return code

AX returns exit code of another program

	AH = 4E

Find first matching file

DS:DX

Location of ASCIIZ string (drive/path/filename) CX = search attribute DTA completed

	AH = 4F

Next matching file

(AH = 4EH called first)

	AH = 50

(DOS internal use)

	AH = 51

(DOS internal use)

	AH = 52

(DOS internal use)

	AH = 53

(DOS internal use)

	AH = 54

Verify state

None

AL–0 if verify off       1 if verify on

	AH = 55

(DOS internal use)

	AH = 56

Rename file

DS:DX = ES:DI =

Address of string for old information Address of string for new information

	AH = 57

Get/set file date/time

AL BX DX and CX

00 (return) 01 (set) File handle Date and time information

	AH = 59

Extended error code

BX =

DOS version (3.0 = 0) AX = error code BH = class of error BL = suggested action CH = where error occurred

	AH = 5A

Create temporary file

DS:DX =

CX = file attribute CF = Set on error AX = error code Points to string

	AH = 5B

Create a new file

(same as previous)

	Note		For DOS versions above 2.0, use AH = 36H for file management.

	Mouse Control Functions Accessed Through Interrupt 33H

	Syntax: INT 33H (when the following parameters are set to the required values)

	AH Value

Function

Input

Output

	AX = 0

Install flag and reset

BX = CX = DX =

If AX = 0 and BX = –1 Mouse support not available AX = –1, then BX = number of supported mouse buttons

	AX = 1

Show pointer

BX = CX = DX =

Does nothing if already visible, otherwise increments the pointer-draw flag by 1 Shows pointer image when pointer-draw flag = 0

	AX = 2

Hide pointer

BX = CX = DX =

Does nothing if already hidden, otherwise decrements the pointer- draw flag Value of –1 hides image

	AX = 3

Get position and button status

BX = CX = DX =

For 2- or 3-button mice, BX returns which button pressed: 0 = leftmost, 1 = rightmost, 2 = center button. Button 3 to 15 reserved. CX = x coordinate; DX = y coordinate of pointer in pixels

	AX = 4

Set pointer position

CX = DX =

New horizontal position in pixels New vertical position in pixels For values that exceed screen boundaries, screen maximum and minimum are used

	AX = 5

Get button press information

BX =

Button status requested, where 0 = leftmost, 1 = rightmost, 2 = center button. AX–bit 0 (leftmost) = 0 or 1        bit 1 (rightmost) = 0 or 1        bit 2 (center) = 0 or 1 If 0 button up, and if 1 button down. BX = number of times button pressed since last call CX = horizontal coordinate of mouse DX = vertical coordinate of mouse

	AX = 6

Get button release information

BX =

Button status requested, same format as for AX = 5 previosly described. AX, BX, CX, and DX as previously described. If 0, button up; 1 if button down

	AX = 7

Set minimum and maximum horizontal position

CX = DX =

Minimum virtual-screen horizontal coordinate in pixels Maximum virtual-screen horizontal coordinate in pixels

	AX = 8

Set minimum and maximum vertical position

DX =

Maximum virtual-screen vertical coordinate in pixels

	AX = 9

Set graphics pointer block

BX= CX = DX = ES =

Pointer hot-spot horizontal coordinate in pixels Pointer hot-spot vertical coordinate in pixels Address of screen/pointer masks Segment of screen/pointer masks

	AX = 10

Set text pointer

BX = CX = DX =

Pointer select value Screen mask value/hardware cursor start scan line Pointer mask value/ hardware cursor stop scan line BX = 0 select software text pointer BX = 1 select hardware cursor CX and DX bit map to: 0 to 7 character 8 to 10 foreground color 11 intensity 12 to 14 background color 15 blinking

	AX = 11

Read mouse motion counters

BX = CX = DX =

CX = horizontal count DX = vertical count Range –32,768 to +32, 768 read in mickeys

	AX = 12

Set user-defined subroutine

CX = DX = ES =

Call mask Offset of subroutine Segment of subroutine CX word bit map: 0 pointer position changed 1 leftmost button pressed 2 leftmost button released 3 rightmost button pressed 4 rightmost button released 5 center button pressed 6 center button released 7 to 15 reserved = 0 Following values loaded when subroutine is called: AX = condition of mask BX = button status CX = pointer horizontal coordinate DX = pointer vertical coordinate SI = last vertical mickey count read DI = last horizontal mickey count read

	AX = 13

Light pen emulation on

BX = CX = DX =

Instructs mouse driver to emulate a light pen Vertical mickey/pixel ratio Ratios specify number of mickeys per 8 pixels

	AX = 14

Light pen emulation off

BX = CX = DX =

Disables mouse driver light pen emulation (Same as AX = 13)

	AX = 15

Set mickey/pixel ratio

CX = DX =

Horizontal mickey/pixel ratio (Same as AX = 13)

	AX = 16

Conditional off

CX = DX = SI = DI =

Left column coordinate in pixels Upper row coordinate in pixels Right column coordinate in pixels Lower row coordinate in pixels Defines an area of the screen for updating

	AX = 19

Set double speed threshold

BX = DX =

Doubles pointer motion Threshold speed in mickeys/second

	AX = 20

Swap user-defined subroutine

CX = DX = ES =

Call mask Offset subroutine Segment of subroutine Sets hardware interrupts for call mask and subroutine address, returns previous values CX word call mask: 0 pointer position changed 1 leftmost button pressed 2 leftmost button released 3 rightmost button pressed 4 rightmost button released 5 center button pressed 6 center button released 7 to 12 reserved = 0 Following values loaded when subroutine is called: AX = condition of mask

BX = button status CX = pointer horizontal coordinate DX = pointer vertical coordinate SI = last vertical mickey count read

DI = last horizontal mickey count read

	AX = 21

Get mouse state storage requirements

BX = CX = DX =

Gets size of buffer in bytes needed to store state of the mouse driver BX = size of buffer in bytes

	AX = 22

Save mouse driver state

BX = CX = DX = ES =

Saves the mouse driver state Offset of buffer Segment of buffer

	AX = 23

Restore mouse driver state

BX = CX = DX = ES =

Restores the mouse driver state from a user buffer Offset of buffer Segment of buffer

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