Int 09h - 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

reg	descr
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