Compaq Evo D500 Technical Reference Manual page 115

Control of the data and clock signals is shared by the 8042and the keyboard depending on the
originator of the transferred data. Note that the clock signal is always generated by the keyboard.
After the keyboard receives a command from the 8042, the keyboard returns an ACK code. If a
parity error or timeout occurs, a Resend command is sent to the 8042.
Table 5-13 lists and describes commands that can be issued by the 8042 to the keyboard.
Table 5–13. 8042-To-Keyboard Commands
Command
Set/Reset Status Indicators
Echo
Invalid Command
Select Alternate Scan Codes
Read ID
Set Typematic Rate/Display
Enable
Default Disable
Set Default
Set Keys - Typematic
Set Keys - Make/Brake
Set Keys - Make
Set Keys - Typematic/Make/Brake
Set Type Key - Typematic
Set Type Key - Make/Brake
Set Type Key - Make
Resend
Reset
Note:
[1] Used in Mode 3 only.
Table 5-13.
8042-To-Keyboard Commands
Value Description
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)
EEh Keyboard returns EEh when previously enabled.
EFh/F1 These commands are not acknowledged.
h
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
F2h Instructs the keyboard to stop scanning and return two
keyboard ID bytes.
F3h Instructs the keyboard to change typematic rate and delay
to specified values:
Bit <7>, Reserved - 0
Bits <6,5>, Delay Time
Bits <4..0>, Transmission Rate:
F4h Instructs keyboard to clear output buffer and last typematic
key and begin key scanning.
F5h Resets keyboard to power-on default state and halts
scanning pending next 8042 command.
F6h Resets keyboard to power-on default state and enable
scanning.
F7h Clears keyboard buffer and sets default scan code set. [1]
F8h Clears keyboard buffer and sets default scan code set. [1]
F9h Clears keyboard buffer and sets default scan code set. [1]
FAh Clears keyboard buffer and sets default scan code set. [1]
FBh Clears keyboard buffer and prepares to receive key ID. [1]
FCh Clears keyboard buffer and prepares to receive key ID. [1]
FDh Clears keyboard buffer and prepares to receive key ID. [1]
FEh 8042 detected error in keyboard transmission.
FFh Resets program, runs keyboard BAT, defaults to Mode 2.
Compaq Deskpro and Evo Personal Computers
Featuring Intel Celeron and Pentium III Processors
Fifth Edition - March 2002
Technical Reference Guide
00 = 250 ms
01 = 500 ms
10 = 750 ms
11 = 1000 ms
00000 = 30.0 ms
00001 = 26.6 ms
00010 = 24.0 ms
00011 = 21.8 ms
:
11111 = 2.0 ms
5-17