The keyboard is simple, and can be configured either to trigger an interrupt on the reception of scancodes or characters. The registers are:
╭─────────┬────╮
│MODIFIERS│0x00│
├─────────┼────┤
│CHARACTER│0x01│
├─────────┼────┤
│SCANCODE │0x02│
├─────────┼────┤
│KBDMODE │0x00│
╰─────────┴────╯
The modes are 0 for character mode (fire interrupt on character reception) and 1 for scancode mode (fire interrupt on scancode reception). The scancode register is 2 bytes long. The modifiers register exposes the modifiers pressed in any given moment in the keyboard: shift, control, alt or logo:
╭──────────┬───────┬──────┬─────┬──────╮
│reserved:4│shift:1│ctrl:1│alt:1│logo:1│
╰──────────┴───────┴──────┴─────┴──────╯