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Technical Reference Guide
Control of the data and clock signals is shared by the 8042 and 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
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Command | Value | Description |
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Set/Reset Status Indicators | EDh | Enables LED indicators. Value EDh is followed by an | ||
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| option byte that specifies the indicator as follows: | ||
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| Bits <7..3> not used |
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| Bit <2>, Caps Lock (0 = off, | 1 = on) | |
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| Bit <1>, NUM Lock (0 = off, | 1 = on) | |
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| 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 | ||
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| and sends an option byte after ACK is received: | ||
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| 01h = Mode 1 |
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| 02h = Mode 2 |
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| 03h = Mode 3 |
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Read ID | F2h | Instructs the keyboard to stop scanning and return two | ||
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| keyboard ID bytes. |
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Set Typematic Rate/Display | F3h | Instructs the keyboard to change typematic rate and delay | ||
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| to specified values: |
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| Bit <7>, Reserved - 0 |
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| Bits <6,5>, Delay Time |
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| 00 = 250 ms |
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| 01 = 500 ms |
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| 10 = 750 ms |
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| 11 = 1000 ms |
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| Bits <4..0>, Transmission Rate: | ||
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| 00000 = 30.0 ms | ||
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| 00001 = 26.6 ms | ||
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| 00010 = 24.0 ms | ||
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| 00011 = 21.8 ms | ||
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| : |
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| 11111 = 2.0 ms |
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Enable | F4h | Instructs keyboard to clear output buffer and last typematic | ||
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| key and begin key scanning. |
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Default Disable | F5h | Resets keyboard to | ||
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| scanning pending next 8042 command. | ||
Set Default | F6h | Resets keyboard to | ||
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| scanning. |
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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 D315 and hp d325 Personal
Featuring the AMD Athlon XP Processor
Second Edition - April 2003