Keyboard Commands; Scan Codes; C.2.5 Keyboard Commands; C.2.6 Scan Codes - HP Compaq d330 DT Technical Reference Manual

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
Command
Key Detection Error/Over/run
BAT Completion
BAT Failure
Echo
Acknowledge (ACK)
Resend
Keyboard ID
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:
/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:
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:
translation must be disabled since translation for this mode cannot be done.
Table C-1.
Keyboard-to-System Commands
Value
00h [1]
FFh [2]
AAh
FCh
EEh
FAh
FEh
83ABh
In Mode 1 operation, the keyboard generates scan codes compatible with 8088-
Mode 2 is the default mode for keyboard operation. In this mode, the 8042 logic
Mode 3 generates a different scan code set from Modes 1 and 2. Code
Changed –- April 2003
Technical Reference Guide
Description
Indicates to the system that a switch closure couldn't be
identified.
Indicates to the system that the BAT has been successful.
Indicates failure of the BAT by the keyboard.
Indicates that the Echo command was received by the
keyboard.
Issued by the keyboard as a response to valid system
inputs (except the Echo and Resend commands).
Issued by the keyboard following an invalid input.
Upon receipt of the Read ID command from the system,
the keyboard issues the ACK command followed by the
two IDS bytes.
hp/Compaq Personal Computers C-11