HP Vectra Technical Reference Manual page 150

The keyboard buffer can store up to 16 entries. Each buffer entry consists of two bytes; an ASCII
character (keycode) and a scancode. The keycode and the scancode are placed in the keyboard
buffer by the INT 09H driver, and the keyboard head pointer is adjusted accordingly. They are
retrieved from the buffer by the INT 16H driver, and the keyboard tail pointer is adjusted.
The keyboard flags are maintained by the INT 09H driver. These flags indicate the state of the
keyboard modifier keys and their respective modes. The byte at memory location 417H indicates
the mode, while the byte at 418H reflects the actual state of the keys themselves. Tables 5.2 and
5.3 list these flags and their meaning.
Table 5.2
Keyboard Flags (Address 417H)
Address Bit Data Definition
00417H 07H
Insert state
Insert mode is active
06H
Caps lock state
Caps lock mode is active
OSH
Num lock state
N·um lock mode is active
04H
Scroll lock state
Scroll lock mode is active
03H
<Alt> key State
< Alt > key is pressed
02H
< CTRL > key State
< CTRL > key is pressed
01H
Left < Shift> key state
Left < Shift> key is pressed
OOH
Right < Shift> key state
Right < Shift> key pressed
Keyboard 141