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09

Category: hardware
Flags: callout or callback (usually hooked rather than called)

INT 09 - IRQ1 - KEYBOARD DATA READY

Desc:	this interrupt is generated when data is received from the keyboard.
	  This is normally a scan code (from either a keypress *or* a key
	  release), but may also be an ACK or NAK of a command on AT-class
	  keyboards.
Notes:	this IRQ may be masked by setting bit 1 on I/O port 21h
	if the BIOS supports an enhanced (101/102-key) keyboard, it calls
	  INT 15/AH=4Fh after reading the scan code (see #00006) from the
	  keyboard and before further processing; all further processing uses
	  the scan code returned from INT 15/AH=4Fh
	the default interrupt handler is at F000h:E987h in 100%-compatible
	  BIOSes
	the interrupt handler performs the following actions for certain
	  special keystrokes:
	    Ctrl-Break	 clear keyboard buffer, place word 0000h in buffer,
			 invoke INT 1B, and set flag at 0040h:0071h
	    SysReq	 invoke INT 15/AH=85h (SysReq is often labeled SysRq)
	    Ctrl-Numlock place system in a tight wait loop until next INT 09
	    Ctrl-Alt-Del jump to BIOS startup code (either F000h:FFF0h or the
			   destination of the jump at that address)
	    Shift-PrtSc	 invoke INT 05
	    Ctrl-Alt-Plus (HP Vectra) enable keyclick
	    Ctrl-Alt-Plus (many clones) set clock speed to high
	    Ctrl-Alt-Minus (HP Vectra) reduce keyclick volume
	    Ctrl-Alt-Minus (many clones) set clock speed to low
	    Ctrl-Alt-SysReq (HP Vectra) generate hard reset
	    Ctrl-Alt-S	(many clones) run BIOS setup program
	    Ctrl-Alt-Esc (many clones) run BIOS setup program
	    Ctrl-Alt-Ins (many clones) run BIOS setup program
	    Ctrl-Alt-LeftShift-GrayMinus (some clones) turn off system cache
	    Ctrl-Alt-LeftShift-GrayPlus (some clones) turn on system cache
	DR DOS hooks this interrupt to control the cursor shape (underscore/
	  half block) for overwrite/insert mode
	DR Multiuser DOS hooks this interrupt for cursor shape control and to
	  control whether Ctrl-Alt-Del reboots the current session or the
	  entire system
SeeAlso: INT 05"PRINT SCREEN",INT 0B"HP 95LX",INT 15/AH=4Fh,INT 15/AH=85h
SeeAlso: INT 16/AH=00h,INT 16/AH=10h,INT 1B,INT 2F/AX=A901h,INT 4A/AH=00h"TI"
SeeAlso: INT 51"DESQview",INT 59"DoubleDOS",INT 79"GO32"


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  Copyright 2000   by Ralf Brown     Updated Jul 2000