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Technical Reference Guide
Compaq Deskpro 4000N and 4000S Personal Computers
First Edition - September 1997
5-33
Table 5-18. CPU Commands To The 8042
(Continued)
Value Command Description
C0h Read input port of the 8042. This command directs the 8042 to transfer the contents of the input port
to the output buffer so that they can be read at port 60h. The contents are as follows:
Bit <7> Password Enable:
0 = Disabled
1 = Enabled
Bit <6> External Boot Enable:
0 = Enabled
1 = Disabled
Bit <5> Setup Enable:
0 = Enabled
1 = Disabled
Bit <4> VGA Enable:
0 = Enabled
1 = Disabled
Bit <3> Diskette Writes:
0 = Disabled
1 = Enabled
Bit <2> Reserved
Bit <1> Pointing Device Data Input Line
Bit <0> Keyboard Data Input Line
C2h Poll Input Port High. This command directs the 8042 to place bits <7..4> of the input port into the
upper half of the status byte on a continous basis until another command is received.
C3h Poll Input Port Low. This command directs the 8042 to place bits <3..0> of the input port into the lower
half of the status byte on a continous basis until another command is received.
D0h Read output port. This command directs the 8042 to transfer the contents of the output port to the
output buffer so that they can be read at port 60h. The contents are as follows:
Bit <7> Keyboard data stream
Bit <6> Keyboard clock
Bit <5> IRQ12 (pointing device interrupt)
Bit <4> IRQ1 (keyboard interrupt)
Bit <3> Pointing device clock
Bit <2> Pointing device data
Bit <1> A20 Control:
0 = Hold A20 low
1 = Enable A20
Bit <0> Reset Line Status;
0 = Inactive
1 = Active
D1h Write output port. This command directs the 8042 to place the next byte written to port 60h into the
output port (only bit <1> can be changed).
D2h Echo keyboard data. Directs the 8042 to send back to the CPU the next byte written to port 60h as if
it originated from the keyboard. No 11-to-9 bit translation takes place but an interrupt (IRQ1) is
generated if enabled.
D3h Echo pointing device data. Directs the 8042 to send back to the CPU the next byte written to port 60h
as if it originated from the pointing device. An interrupt (IRQ12) is generated if enabled.
D4h Write to pointing device. Directs the 8042 to send the next byte written to 60h to the pointing device.
E0h Read test inputs. Directs the 8042 to transfer the test bits 1 and 0 into bits <1,0> of the output buffer.
F0h-
FFh
Pulse output port. Controls the pulsing of bits <3..0> of the output port (0 = pulse, 1 = don’t pulse).
Note that pulsing bit <0> will reset the system.