Technical Reference Guide www.hp.com 5-19
Input/Output Interfaces
Table 5-16 lists and describes commands that can be issued by the 8042 to the keyboard.
Table 5-16.
8042-To-Keyboard Commands
Command Value Description
Set/Reset Status Indicators EDh Enables LED indicators. Value EDh is followed by an option
byte that specifies the indicator as follows:
Bits <7..3> not used
Bit <2>, Caps Lock (0 = off, 1 = on)
Bit <1>, NUM Lock (0 = off, 1 = on)
Bit <0>, Scroll Lock (0 = off, 1 = on)
Echo EEh Keyboard returns EEh when previously enabled.
Invalid Command EFh/F1h These commands are not acknowledged.
Select Alternate Scan Codes F0h Instructs the keyboard to select another set of scan codes
and sends an option byte after ACK is received:
01h = Mode 1
02h = Mode 2
03h = Mode 3
Read ID F2h Instructs the keyboard to stop scanning and return two
keyboard ID bytes.
Set Typematic Rate/Display F3h Instructs the keyboard to change typematic rate and delay to
specified values:
Bit <7>, Reserved—0
Bits <6,5>, Delay Time
00 = 250 ms
01 = 500 ms
10 = 750 ms
11 = 1000 ms
Bits <4..0>, Transmission Rate:
00000 = 30.0 ms
00001 = 26.6 ms
00010 = 24.0 ms
00011 = 21.8 ms
:
11111 = 2.0 ms
Enable F4h Instructs keyboard to clear output buffer and last typematic
key and begin key scanning.
Default Disable F5h Resets keyboard to power-on default state and halts scanning
pending next 8042 command.
Set Default F6h Resets keyboard to power-on default state and enable
scanning.
Set Keys—Typematic F7h Clears keyboard buffer and sets default scan code set. [1]
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