Input/Output Interfaces

 

Table 5-15. (Continued)

 

CPU Commands to the 8042

 

 

Value

Command Description

 

 

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.

 

 

 

5-20

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