●8042 Keyboard Controller

IO Port 60h為鍵盤的輸入暫存器 、61h為控制暫存器、64h狀態暫存器
8042 - Keyboard Controller
8042 Status Register (port 64h read)
8042 Status Register
Bit0|------output register (60h) has data for system
Bit1|------input register (60h/64h) has data for 8042
Bit2|------system flag (set to 0 after power on reset)
Bit3|------data in input register is command (1) or data (0)
Bit4|------1=keyboard enabled, 0=keyboard disabled (via switch)
Bit5|------1=transmit timeout (data transmit not complete)
Bit6|------1=receive timeout (data transmit not complete)
Bit7|------1=even parity rec'd, 0=odd parity rec'd (should be odd)

Port Mode Description

64h read 8042 status register. Can be read at any time. See table above for more information.
64h write 8042 command register. Writing this port sets Bit3 of the status register to 1 and the byte is treated as a controller command. Devices attached to the 8042 should be disabled before issuing commands that return data since data in the output register will be overwritten.
60h read 8042 output register (should only be read if Bit 0 of status port is set to 1)
60h write 8042 data register. Data should only be written if Bit 1 of the status register is zero (register is empty).
When this port is written Bit 3 of the status register is set to zero and the byte is treated as a data. The 8042 uses this byte if it's expecting data for a previous command, otherwise the data is written directly to the keyboard. See ~KEYBOARD COMMANDS~ for information on
programming the actual keyboard hardware.

8042 Commands Related to PC Systems (Port 64h)

Command Description

20 Read 8042 Command Byte: current 8042 command byte is placed in port 60h.
60 Write 8042 Command Byte: next data byte written to port 60h is placed in 8042 command register. Format:

8042 Command Byte
Bit0|------1=enable output register full interrupt
Bit1|------ should be 0
Bit2|------1=set status register system, 0=clear
Bit3|------ 1=override keyboard inhibit, 0=allow inhibit
Bit4|------disable keyboard I/O by driving clock line low
Bit5|------ disable auxiliary device, drives clock line low
Bit6|------IBM scancode translation 0=AT, 1=PC/XT
Bit7|------reserved, should be 0

A4 Password Installed Test: returned data can be read from port 60h; FA=password installed, F1=no password
A5 Load Security: bytes written to port 60h will be read until a null (0) is found.
A6 Enable Security: works only if a password is already loaded
A7 Disable Auxiliary Interface: sets Bit 5 of command register stopping auxiliary I/O by driving the clock line low
A8 Enable Auxiliary Interface: clears Bit 5 of command register
A9 Auxiliary Interface Test: clock and data lines are tested; results placed at port 60h are listed below:

00 no error
01 keyboard clock line is stuck low
02 keyboard clock line is stuck high
03 keyboard data line is stuck low
04 keyboard data line is stuck high

AA Self Test: diagnostic result placed at port 60h, 55h=OK
AB Keyboard Interface Test: clock and data lines are tested; results placed at port 60h are listed above with command A9
AC Diagnostic Dump: sends 16 bytes of 8042's RAM, current input port state, current output port state and 8042 program status
word to port 60h in scan-code format.
AD Disable Keyboard Interface: sets Bit 4 of command register stopping keyboard I/O by driving the clock line low
AE Enable Keyboard Interface: clears Bit 4 of command register enabling keyboard interface.
C0 Read Input Port: data is read from its input port (which is inaccessible to the data bus) and written to output register at port 60h; output register should be empty before call.

8042 Input Port
Bit0-3|------undefined
Bit4|------ 1=enable 2nd 256K of motherboard RAM, 0=disable
Bit5|------1=manufacturing jumper not installed, 0=installed
Bit6|------ 1=primary display is MDA, 0=primary display is CGA
Bit7|------1=keyboard not inhibited, 0=keyboard inhibited

C1 Poll Input Port Low Bits: Bits 0-3 of port 1 placed in status Bits 4-7
C2 Poll Input Port High Bits: Bits 4-7 of port 1 placed in status Bits 4-7
D0 Read Output Port: data is read from 8042 output port (which is inaccessible to the data bus) and placed in output register;
the output register should be empty. (see command D1 below)
D1 Write Output Port: next byte written to port 60h is placed in the 8042 output port (which is inaccessible to the data bus)

8042 Output Port
Bit0|------system reset line
Bit1|------gate A20
Bit2-3|------undefined
Bit4|------ output buffer full
Bit5|------input buffer empty
Bit6|------keyboard clock (output)
Bit7|------keyboard data (output)

D2 Write Keyboard Output Register: on PS/2 systems the next data
byte written to port 60h input register is written to port 60h
output register as if initiated by a device; invokes interrupt
if enabled
D3 Write Auxiliary Output Register: on PS/2 systems the next data
byte written to port 60h input register is written to port 60h
output register as if initiated by a device; invokes interrupt
if enabled
D4 Write Auxiliary Device: on PS/2 systems the next data byte
written to input register a port at 60h is sent to the
auxiliary device
E0 Read Test Inputs: 8042 reads its T0 and T1 inputs; data is
placed in output register; Bit 0 is T0, Bit 1 is T1:

Test Input Port Bits
Bit0|------keyboard clock
Bit1|------keyboard data

Fx Pulse Output Port: Bits 0-3 of the 8042 output port can be pulsed low for 6 us(微秒);Bits 0-3 of command indicate which Bits should be pulsed; 0=pulse, 1=don't pulse; pulsing
Bit 0 results in CPU reset since it is connected to system reset line.