Compaq W4000 manual Keyboard Commands, Scan Codes, Table C-1, Keyboard-to-System Commands

Technical Reference Guide

C.2.5 KEYBOARD COMMANDS

Table C-1 lists the commands that the keyboard can send to the system (specifically, to the 8042- type logic).

Table C–1.Keyboard-to-System Commands

		Table C-1.
	Keyboard-to-System Commands
Command	Value	Description
Key Detection Error/Over/run	00h [1]	Indicates to the system that a switch closure couldn’t be
	FFh [2]	identified.
BAT Completion	AAh	Indicates to the system that the BAT has been successful.
BAT Failure	FCh	Indicates failure of the BAT by the keyboard.
Echo	EEh	Indicates that the Echo command was received by the
		keyboard.
Acknowledge (ACK)	FAh	Issued by the keyboard as a response to valid system
		inputs (except the Echo and Resend commands).
Resend	FEh	Issued by the keyboard following an invalid input.
Keyboard ID	83ABh	Upon receipt of the Read ID command from the system,
		the keyboard issues the ACK command followed by the
		two IDS bytes.

Note:

[1]Modes 2 and 3.

[2]Mode 1 only.

C.2.6 SCAN CODES

The scan codes generated by the keyboard processor are determined by the mode the keyboard is operating in.

♦Mode 1: In Mode 1 operation, the keyboard generates scan codes compatible with 8088- /8086-based systems. To enter Mode 1, the scan code translation function of the keyboard controller must be disabled. Since translation is not performed, the scan codes generated in Mode 1 are identical to the codes required by BIOS. Mode 1 is initiated by sending command F0h with the 01h option byte. Applications can obtain system codes and status information by using BIOS function INT 16h with AH=00h, 01h, and 02h.

♦Mode 2: Mode 2 is the default mode for keyboard operation. In this mode, the 8042 logic translates the make codes from the keyboard processor into the codes required by the BIOS. This mode was made necessary with the development of the Enhanced III keyboard, which includes additional functions over earlier standard keyboards. Applications should use BIOS function INT 16h, with AH=10h, 11h, and 12h for obtaining codes and status data. In Mode 2, the keyboard generates the Break code, a two-byte sequence that consists of a Make code immediately preceded by F0h (i.e., Break code for 0Eh is “F0h 0Eh”).

♦Mode 3: Mode 3 generates a different scan code set from Modes 1 and 2. Code translation must be disabled since translation for this mode cannot be done.

Compaq Personal Computers C-11

Changed –- July 2000