Compaq 850 manual To-Keyboard Commands

Technical Reference Guide

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

		Table 5-13.
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/F1	These commands are not acknowledged.
	h
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]
Set Keys - Make/Brake	F8h	Clears keyboard buffer	and sets default scan code set. [1]
Set Keys - Make	F9h	Clears keyboard buffer	and sets default scan code set. [1]
Set Keys - Typematic/Make/Brake	FAh	Clears keyboard buffer	and sets default scan code set. [1]
Set Type Key - Typematic	FBh	Clears keyboard buffer and prepares to receive key ID. [1]
Set Type Key - Make/Brake	FCh	Clears keyboard buffer and prepares to receive key ID. [1]
Set Type Key - Make	FDh	Clears keyboard buffer and prepares to receive key ID. [1]
Resend	FEh	8042 detected error in keyboard transmission.
Reset	FFh	Resets program, runs keyboard BAT, defaults to Mode 2.

Note:

[1] Used in Mode 3 only.

Compaq Deskpro EXS and Workstation 300 Personal Computers 5-17

Featuring the Intel Pentium 4 Processor

First Edition - December 2000