KBC Commands
Keyboard Controller Commands
The commands accepted by a PC keyboard controller
This page details just the commands that a PC keyboard controller accepts. To send a command or read some results reliably see the sections on reading and writing the controller in the keyboard controller page.
The Commands
The controller accepts the commands shown in this table. The command itself is sent to port 0x64. Any following bytes of data - represented by X in the table - are sent to port 0x60.
Note that these are commands to the keyboard controller, not those sent to the keyboard or to the mouse.
| Command Value | AT Architecture | PS/2 Architecture | Description of Command |
|---|---|---|---|
| 0x20 | Yes (ph) | Yes (ph) | Read command byte (ph) |
| 0x20 .. 0x3F | Yes (misa) | Read internal RAM location (misa) | |
| 0x60 X | Yes (ph) | Yes (ph) | Write X to command byte (ph) |
| 0x60 .. 0x7F X | Yes (misa) | Write X to RAM location (misa) | |
| 0xA4 | No (ph) | Yes (ph) | Test if password installed. Result is 0xF1 = no, 0xFA = yes (ph) |
| 0xA5 X…X0 | No (ph) | Yes (ph) | Load password scan codes until a zero byte (ph) |
| 0xA6 | No (ph) | Yes (ph) | Enable the password (ph) |
| 0xA7 | No (ph) | Yes (ph) | Disable the mouse. Sets bit 5 of the command byte (ph) |
| 0xA8 | No (ph) | Yes (ph) | Enable the mouse. Clears bit 5 of the command byte (ph) |
| 0xA9 | No (ph) | Yes (ph) | Test the mouse. Result is 0 -> no error, 1 -> clock stuck low, 2 -> clock stuck high, 3 -> data line stuck low, 4 -> data line stuck high (ph) Test the mouse clock and data lines (misa) |
| 0xAA | Yes (ph) | Yes (ph) | Self test. Result is 0x55 if no errors (ph) |
| 0xAB | Yes (ph) | Yes (ph) | Test interface (to keyboard?). Result is 0 -> no error, 1 -> clock stuck low, 2 -> clock stuck high, 3 -> data line stuck low, 4 -> data line stuck high (ph) Test keyboard clock and data lines (misa) |
| 0xAC | Yes (ph) | No (ph) | Diagnostic dump 16 bytes of controller's RAM (ph) |
| 0xAD | Yes (ph) | Yes (ph) | Disable keyboard. Sets bit 4 of the command byte (ph) Disable keyboard interface (misa) |
| 0xAE | Yes (ph) | Yes (ph) | Enable keyboard. Clears bit 4 of the command byte (ph) Enable keyboard interface (misa) |
| 0xC0 | Yes (ph) | Yes (ph) | Read input port (to output buffer) (ph) |
| 0xC1 | No (ph) | Yes (ph) | Input port bits 3 :- 0 to status bits 7 :- 4 (ph) |
| 0xC2 | No (ph) | Yes (ph) | Input port bits 7 :- 4 to status bits 7 :- 4 (ph) |
| 0xD0 | Yes (ph) | Yes (ph) | Read output port (to output buffer) (ph) |
| 0xD1 X | Yes (ph) | Yes (ph) | Write X to output port. Beware not to clear system reset bit 0 (ph) |
| 0xD2 X | No (ph) | Yes (ph) | Write X to output buffer as if sent by the keyboard. An interrupt occurs (ph) Interrupt occurs if the keyboard interface is enabled (misa) |
| 0xD3 X | No (ph) | Yes (ph) | Write X to output buffer as if sent by the mouse. An interrupt occurs (ph) Interrupt occurs if the mouse interface is enabled (misa) |
| 0xD4 X | No (ph) | Yes (ph) | Write X to the mouse (ph) |
| 0xE0 | Yes (ph) | Yes (ph) | Read test inputs T1, T0 to bits 1 and 0 of output buffer (ph) Bits 1 :- 0 get mouse clock and keyboard clock respectively (misa) |
| 0xF0 .. 0xFF | Yes (ph) | Yes (ph) | Pulse output port. Bits 3 :: 0 pulse bits 3 :: 0 of the output port (ph). Ports are pulsed low for approximately six microseconds. A zero says to pulse the bit. A one says not to change it. (misa) |
Sources
Sources of information in the table above are
- (ph) - PC Programmer's Handbook – Second edition
- (misa) - Mindshare ISA System Architecture
page revision: 1, last edited: 26 Aug 2015 21:43