NEC PC Programmers Reference/PC-98xx Series Programmers Reference/Interrupt 0x18 - Keyboard

The Keyboard BIOS emits an Interrupt 0x9 when key is pressed. Keyboard data may be treated by invoking INT 0x18.

How BIOS Manages Keys

BIOS maintains an array of data ("keyboard status table"), with a bit for each key. When key is down, bit is 1; when up, bit is 0. When key is pressed, index of key in input status array is combined with code for SHIFT status to produce key scan code (which is how programs recognize keys).

PC-98 Keyboard BIOS is IBM-compliant.

List of Key Access Commands

AH	Command	Purpose	Use
0x1	Sense First Key	Queries keyboard for keypresses. Returns key at back of buffer.	Returns Key scan code to AH JIS code of key to AL BX = 0 if buffer empty; 1 if presses queued.
0x2	Examine Modifier Keys	Returns status of key modifiers (SHIFT, CTRL, GRPH, CAPSLOCK, KANA)	Returns modifier status byte in AL SHIFT down = b0 CAPS = b1 KANA = b2 GRPH = b3 CTRL = b4
0x3	Initialize Keyboard	Install built-in keyboard driver interface. Sets aside memory for BIOS use of keyboard; resets uPD8251A.
0x4	Get Key Group Status	Queries the keyboard state table for the immediate state of a set of keys. Returns the byte for the key group requested, which in turn can be masked with logical AND to find the state of individual keys.	key group number to AL Returns key group status byte to AH
0x5	Sense Last Key	Queries keyboard for keypresses. Returns key at front of buffer.	Returns Key scan code to AH JIS code of key to AL BX = 0 if buffer empty; 1 if presses queued.
0x6	Init Keyboard Buffer / Pending Keys Clear	Sets up keyboard buffer. Calling this will clear the buffer.
0x7	Handle First Key	Get the first key pressed not yet handled and removes it from the buffer.	Returns AH = key scan code AL = JIS code of key BL = key modifiers byte
0x8	Handle Last Key	Gets the last key pressed and removes it from the buffer.	Returns AH = key scan code AL = JIS code of key BL = key modifiers byte
0x9	Simulate Key Press	Creates a simulated keypress by filling the keyboard buffer with designated data.	AL = desired key code BL = modifier keys state byte Returns Key scan code to AH JIS code of key to AL