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.