Technical Reference Guide
361834-002
5-21
Input/Output Interfaces
The keyboard interface configuration registers are listed in the following table:
8042 Control
The BIOS function INT 16 is typically used for controlling interaction with the keyboard.
Sub-functions of INT 16 conduct the basic routines of handling keyboard data (i.e., translating
the keyboard's scan codes into ASCII codes). The keyboard/pointing device interface is accessed
by the CPU through I/O mapped ports 60h and 64h, which provide the following functions:
■
Output buffer reads
■
Input buffer writes
■
Status reads
■
Command writes
Ports 60h and 64h can be accessed using the IN instruction for a read and the OUT instruction for
a write. Prior to reading data from port 60h, the “Output Buffer Full” status bit (64h, bit <0>)
should be checked to ensure data is available. Likewise, before writing a command or data, the
“Input Buffer Empty” status bit (64h, bit <1>) should also be checked to ensure space is
available.
I/O Port 60h
I/O port 60h is used for accessing the input and output buffers. This register is used to send and
receive data from the keyboard and the pointing device. This register is also used to send the
second byte of multi-byte commands to the 8042 and to receive responses from the 8042 for
commands that require a response.
A read of 60h by the CPU yields the byte held in the output buffer. The output buffer holds data
that has been received from the keyboard and is to be transferred to the system.
A CPU write to 60h places a data byte in the input byte buffer and sets the CMD/ DATA bit of the
Status register to DATA. The input buffer is used for transferring data from the system to the
keyboard. All data written to this port by the CPU will be transferred to the keyboard except
bytes that follow a multibyte command that was written to 64h
Table 5-17.
Keyboard Interface Configuration Registers
Index
Address Function
R/W
30h
Activate
R/W
70h
Primary Interrupt Select
R/W
72h
Secondary Interrupt Select
R/W
F0h
Reset and A20 Select
R/W
Summary of Contents for Compaq dc71 Series
Page 50: ...2 34 361834 002 Technical Reference Guide System Overview ...
Page 58: ...3 8 361834 002 Technical Reference Guide Processor Memory Subsystem ...
Page 126: ...5 40 361834 002 Technical Reference Guide Input Output Interfaces ...
Page 168: ...8 20 361834 002 Technical Reference Guide BIOS ROM ...
Page 188: ...A 20 361834 002 Technical Reference Guide Error Messages and Codes ...
Page 192: ...B 4 361834 002 Technical Reference Guide ASCII Character Set ...
Page 210: ...C 18 361834 002 Technical Reference Guide Keyboard ...
