BIOS call

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BIOS Interrupt Calls are a facility that DOS programs, and some other software such as boot loaders, use to invoke the BIOS's facilities. Some operating systems also use the BIOS to probe and initialise hardware resources during their early stages of booting.

Contents

Interrupt Table

Interrupt Description
INT 00h-- CPU: Executed after an attempt to divide by zero or when the quotient does not fit in the destination
INT 01h CPU: Executed after every instruction while the trace flag is set
INT 02h CPU: NMI, used e.g. by POST for memory errors
INT 03h CPU: The lowest non-reserved interrupt, it is used exclusively for debugging, and the INT 03 handler is always implemented by a debugging program
INT 04h CPU: Numeric Overflow. Usually caused by the INTO instruction when the overflow flag is set.
INT 05h Executed when Shift-PrintScreen is pressed, as well as when the BOUND instruction detects a bound failure.
INT 06h CPU: Called when the Undefined Opcode (invalid instruction) exception occurs. Usually installed by the operating system.
INT 07h CPU: Called when an attempt was made to execute a floating-point instruction and no numeric coprocessor was available.
INT 08h IRQ0: Implemented by the system timing component; called 18.2 times per second (once every 55 ms) by the PIC
INT 09h IRQ1: Called after every key press and release (as well as during the time when a key is being held)
INT 0Bh IRQ3: Called by serial ports 2 and 4 (COM2/4) when in need of attention
INT 0Ch IRQ4: Called by serial ports 1 and 3 (COM1/3) when in need of attention
INT 0Dh IRQ5: Called by hard disk controller (PC/XT) or 2nd parallel port LPT2 (AT) when in need of attention
INT 0Eh IRQ6: Called by floppy disk controller when in need of attention
INT 0Fh IRQ7: Called by 1st parallel port LPT1 (printer) when in need of attention
INT 10h Video Services - installed by the BIOS or operating system; called by software programs
AH=00h Set Video Mode
AH=01h Set Cursor Shape
AH=02h Set Cursor Position
AH=03h Get Cursor Position And Shape
AH=04h Get Light Pen Position
AH=05h Set Display Page
AH=06h Clear/Scroll Screen Up
AH=07h Clear/Scroll Screen Down
AH=08h Read Character and Attribute at Cursor
AH=09h Write Character and Attribute at Cursor
AH=0Ah Write Character at Cursor
AH=0Bh Set Border Color
AH=0Eh Write Character in TTY Mode
AH=0Fh Get Video Mode
AH=13h Write String
INT 11h Installed by the BIOS; returns equipment list
INT 12h Installed by the BIOS or operating system; returns Conventional Memory Size
INT 13h Low Level Disk Services; installed by the BIOS or operating system; called by software programs
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=05h Format Track On Drive
AH=08h Get Drive Parameters
AH=09h Init Fixed Drive Parameters
AH=0Ch Seek To Specified Track
AH=0Dh Reset Fixed Disk Controller
AH=15h Get Drive Type
AH=16h Get Floppy Drive Media Change Status
INT 14h Routines for communicating via the serial port. Used by software programs.
AH=00h Serial Port Initialization
AH=01h Transmit Character
AH=02h Receive Character
AH=03h Status
INT 15h Miscellaneous (System services support routines)
AH=4FH Keyboard Intercept
AH=83H Event Wait
AH=84H Read Joystick
AH=85H Sysreq Key Callout
AH=86H Wait
AH=87H Move Block
AH=88H Get Extended Memory Size
AH=C0H Get System Parameters
AH=C1H Get Extended BIOS Data Area Segment
AH=C2H Pointing Device Functions
AH=0E8h, AL=01h (AX = 0E801h) Get Extended Memory Size(Newer function, since 1994). Gives results for memory size above 64 Mb.
INT 16h Implemented by the BIOS or operating system. Provides routines to be called by software programs which communicate with the keyboard.
AH=00h Read Character
AH=01h Read Input Status
AH=02h Read Keyboard Shift Status
AH=10h Read Character Extended
AH=11h Read Input Status Extended
AH=12h Read Keyboard Shift Status Extended
INT 17h Print Services - used by software programs to communicate with the printer
AH=00h Print Character to Printer
AH=01h Initialize Printer
AH=02h Check Printer Status
INT 18h Execute Cassette BASIC: True IBM computers contain BASIC in the ROM to be interpreted and executed by this routine in the event of a boot failure (called by the BIOS)
INT 19h After POST this interrupt is used by BIOS to load the operating system.
INT 1Ah Real Time Clock Services - called by software programs to communicate with the RTC
AH=00h Read RTC
AH=01h Set RTC
AH=02h Read RTC Time
AH=03h Set RTC Time
AH=04h Read RTC Date
AH=05h Set RTC Date
AH=06h Set RTC Alarm
AH=07h Reset RTC Alarm
INT 1Bh Installed by the operating system; automatically called by INT 9 when Ctrl-Break has been pressed
INT 1Ch Called automatically by INT 08; available for use by software programs when a routine needs to be executed regularly
INT 1Dh Not to be called; simply a pointer to the VPT (Video Parameter Table), which contains data on video modes
INT 1Eh Not to be called; simply a pointer to the DPT (Diskette Parameter Table), containing a variety of information concerning the diskette drives
INT 1Fh Not to be called; simply a pointer to the VGCT (Video Graphics Character Table), which contains the data for ASCII characters 80h to FFh
INT 41h Address pointer: FDPT = Fixed Disk Parameter Table (1st hard drive)
INT 46h Address pointer: FDPT = Fixed Disk Parameter Table (2nd hard drive)
INT 4Ah Called by RTC for alarm
INT 70h IRQ8: Called by RTC
INT 74h IRQ12: Called by mouse
INT 75h IRQ13: Called by math coprocessor
INT 76h IRQ14: Called by primary IDE controller
INT 77h IRQ15: Called by secondary IDE controller

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. (At the time the original IBM PC was released in 1981, the BASIC in ROM was a key feature.) As time went on and BASIC was no longer shipped on all PCs, this interrupt would simply display an error message indicating that no bootable volume was found (famously, "No ROM BASIC", or more self-explanatory messages in later BIOS versions); in other BIOS versions it would prompt the user to insert a bootable volume and press a key, and then after the user did so it would loop back to the bootstrap loader to try booting again.

See also

External links

Wikipedia content modification information:

  • This page was last modified on 3 December 2008, at 00:39.

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