"8042" PS/2 Controller: Difference between revisions
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== PS/2 Controller Commands ==
The PS/2 Controller accepts some commands and performs them. These commands should not be confused with bytes sent to a PS/2 device (e.g. keyboard, mouse).
To send a command to the controller, write the command byte to IO port 0x64. If there is a "next byte" (the command is 2 bytes) then the next byte needs to be written to IO Port 0x60. If there is a response byte, then the response byte needs to be read from IO Port 0x60.
{| {{wikitable}}
|-
! Command Byte
! Meaning
! Response Byte
|-
|0x20
|Read "byte 0" from internal RAM
|Controller Configuration Byte (see below)
|-
|0x21 to 0x3F
|Read "byte N" from internal RAM (where 'N' is the command byte & 0x1F)
|Unknown (only the first byte of internal RAM has a standard purpose)
|-
|0x60
|Write next byte to "byte 0" of internal RAM (Controller Configuration Byte, see below)
|None
|-
|0x61 to 0x7F
|Write next byte to "byte N" of internal RAM (where 'N' is the command byte & 0x1F)
|None
|-
|0xA7
|Disable second PS/2 port (only if 2 PS/2 ports supported)
|None
|-
|0xA8
|Enable second PS/2 port (only if 2 PS/2 ports supported)
|None
|-
|0xA9
|Test second PS/2 port (only if 2 PS/2 ports supported)
|0x00 test passed
0x01 clock line stuck low
0x02 clock line stuck high
0x03 data line stuck low
0x04 data line stuck high
|-
|0xAA
|Test PS/2 Controller
|0x55 test passed
0xFC test failed
|-
|0xAB
|Test first PS/2 port
|0x00 test passed
0x01 clock line stuck low
0x02 clock line stuck high
0x03 data line stuck low
0x04 data line stuck high
|-
|0xAC
|Diagnostic dump (real all bytes of internal RAM)
|Unknown
|-
|0xAD
|Disable first PS/2 port
|None
|-
|0xAE
|Enable first PS/2 port
|None
|-
|0xC0
|Read controller input port
|Unknown (none of these bits have a standard/defined purpose)
|-
|0xC1
|Copy bits 0 to 3 of input port to status bits 4 to 7
|None
|-
|0xC2
|Copy bits 4 to 6 of input port to status bits 4 to 7
|None
|-
|0xD0
|Read Controller Output Port
|Controller Output Port (see below)
|-
|0xD1
|Write next byte to Controller Output Port (see below)
Note: Check if output buffer is empty first
|None
|-
|0xD2
|Write next byte to first PS/2 port output buffer (only if 2 PS/2 ports supported)
(makes it look like the byte written was received from the first PS/2 port)
|None
|-
|0xD3
|Write next byte to second PS/2 port output buffer (only if 2 PS/2 ports supported)
(makes it look like the byte written was received from the second PS/2 port)
|None
|-
|0xD4
|Write next byte to second PS/2 port input buffer (only if 2 PS/2 ports supported)
(sends next byte to the second PS/2 port)
|None
|-
|0xF0
|Pulse output line low for 6 ms. Bits 0 to 3 are used as a mask (0 = pulse line, 1 = don't pulse line) and correspond to 4 different output lines.
Note: Bit 0 corresponds to the "reset" line. The other output lines don't have a standard/defined purpose.
|None
|}
=== PS/2 Controller Configuration Byte ===
Commands 0x20 and 0x60 let you read and write the PS/2 Controller Configuration Byte. This configuration byte has the following format:
{| {{wikitable}}
|-
! Bit
! Meaning
|-
| 0
| First PS/2 port interrupt (1 = enabled, 0 = disabled)
|-
| 1
| Second PS/2 port interrupt (1 = enabled, 0 = disabled, only if 2 PS/2 ports supported)
|-
| 2
| Unknown
|-
| 3
| Should be zero
|-
| 4
| First PS/2 port clock (1 = disabled, 0 = enabled)
|-
| 5
| Second PS/2 port clock (1 = disabled, 0 = enabled, only if 2 PS/2 ports supported)
|-
| 6
| First PS/2 port translation (1 = enabled, 0 = disabled)
|-
| 7
| Must be zero
|-
|}
=== PS/2 Controller Output Port ===
Commands 0xD0 and 0xD1 let you read and write the PS/2 Controller Output Port. This output port has the following format:
{| {{wikitable}}
|-
! Bit
! Meaning
|-
| 0
| System reset (output)
'''WARNING''' always set to '1'. You need to pulse the reset line (e.g. using command 0xFE), and setting this bit to '0' can lock the computer up ("reset forever").
|-
| 1
| A20 gate (output)
|-
| 2
| Second PS/2 port clock (output, only if 2 PS/2 ports supported)
|-
| 3
| Second PS/2 port data (output, only if 2 PS/2 ports supported)
|-
| 4
| Output buffer full with byte from first PS/2 port (connected to IRQ1)
|-
| 5
| Output buffer full with byte from second PS/2 port (connected to IRQ12, only if 2 PS/2 ports supported)
|-
| 6
| First PS/2 port clock (output)
|-
| 7
| First PS/2 port data (output)
|-
|}
| |||