Technical Reference Guide www.hp.com 5-23
Input/Output Interfaces
A9h Test the clock and data lines of the pointing device interface and place test results in the output
buffer.
00h = No error detected
01h = Clock line stuck low
02h = Clock line stuck high
03h = Data line stuck low
04h = Data line stuck high
AAh Initialization. This command causes the 8042 to inhibit the keyboard and pointing device and
places 55h into the output buffer.
ABh Test the clock and data lines of the keyboard interface and place test results in the output buffer.
00h = No error detected
01h = Clock line stuck low
02h = Clock line stuck high
03h = Data line stuck low
04h = Data line stuck high
ADh Disable keyboard command (sets bit <4> of the 8042 command byte).
AEh Enable keyboard command (clears bit <4> of the 8042 command byte).
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.
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.
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.
Table 5-18. (Continued)
CPU Commands to the 8042
Value Command Description
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