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Copyright 1991 David Jurgens |
INT 9 - 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
related interrupts:
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
- see MAKE CODES KB FLAGS
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| Esc or Alt-X to exit |
int 9 |
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