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BIOS interrupt call

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BIOS Interrupt Calls are a facility that MS-DOS programs use to invoke the BIOS's facilities.

Contents
1 Interrupt Table
2 Descriptions

2.1 INT 13h: Low Level Disk Services

2.1.1 INT 13h AH=00h: Reset Disk Drives
2.1.2 INT 13h AH=01h: Check Drive Status
2.1.3 INT 13h AH=02h: Read Sectors From Drive

2.2 INT 18h: Execute BASIC
2.3 INT 21h: MS-DOS Functions

2.3.1 INT 21h AH=00h: Exit To Shell
2.3.2 INT 21h AH=01h: Read Input From Keyboard
2.3.3 INT 21h AH=02h: Write Character To Output

2.4 See also

Interrupt Table

Interrupt Description
INT 5h Print Screen
INT 10h Video Services
AH=00h Set Video Mode
AH=01h Set Cursor Shape
AH=02h Position Cursor
AH=03h Get Cursor Position And Shape
AH=04h Get Light Pen Position
AH=05h Set Display Page
AH=06h Clear/Scroll Up Screen
AH=07h Clear/Scroll Down Screen
AH=08h Read Character From Screen
AH=09h Write Character(s) To Screen
AH=0Ah Write Character To Screen With Existing Attribute
AH=0Bh Set Border Color
AH=0Eh Write Character To Screen With Existing Attribute And Reposition
AH=0Fh Get Video Mode
INT 11h Equipment Installed
INT 12h Memory Available
INT 13h Low Level Disk Services
AH=00h Reset Disk Drives
AH=01h Check Drive Status
AH=02h Read Sectors From Drive
AH=03h Write Sectors To Drive
AH=04h Verifies Sectors On Drive
AH=0Ch Moves Disk Head To Specified Track
AH=0Dh Resets Hard Disk Controller
INT 14h Serial I/O
AH=00h Serial Port Initialization
AH=01h Transmit Character
AH=02h Receive Character
AH=03h Status
INT 15h Miscellaneous
INT 16h Keyboard
AH=00h Input Key From Keyboard
AH=01h Check For Input Availability
AH=02h Check Keyboard Shift Status
INT 17h Print Services
AH=00h Print Character To Printer
AH=01h Initialize Printer
AH=02h Check Printer Status
INT 18h Execute BASIC
INT 19h Reboot
INT 1Ah Real Time Clock Services
AH=00h Read RTC
AH=01h Set RTC
INT 21h MS-DOS Functions
AH=00h Exit To Shell
AH=01h Read Input From Keyboard
AH=02h Write Character To Output

Descriptions

INT 13h: Low Level Disk Services

INT 13h AH=00h: Reset Disk Drives

Parameters:

AH 00h
DL Drive Index

INT 13h AH=01h: Check Drive Status

Parameters:

AH 01h

Results:

AL Return Code
00h Success
01h Invalid Command
02h Cannot Find Address Mark
03h Attempted Write On Write Protected Disk
04h Sector Not Found
05h Reset Failed

INT 13h AH=02h: Read Sectors From Drive

Parameters:

AH 02h
AL Sectors To Read Count
CH Track
CL Sector
DH Head
DL Drive
ES:BX Buffer Address Pointer

Results:

CF Set On Error, Clear If No Error
AH Return Code
AL Actual Sectors Read Count

INT 18h: Execute BASIC

Description:

This interrupt traditionally jumped to an implementation of BASIC stored in ROM. This call would typically be invoked if the BIOS was unable to identify any bootable volumes on startup. As time went on and BASIC was no longer shipped on all PCs, this interrupt would simply prompt the user to insert a bootable volume and press a key.

INT 21h: MS-DOS Functions

INT 21h AH=00h: Exit To Shell

Parameters:

AH 00h

INT 21h AH=01h: Read Input From Keyboard

Parameters:

AH 01h

Results:

AL ASCII Value Of Character Read


INT 21h AH=02h: Write Character To Output

Parameters:

AH 02h
DL Character To Output

See also

Last updated: 05-25-2005 00:47:33
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