Information Technology Reference
In-Depth Information
(3) KBD Reset
(5) +5V
(1) KBD Clock
(4) GND
Y-Decoder
(2) KDB Data
IRQ1
11-bit
SDU
code
D0-D7
Scan matrix
Figure 10.5
Keyboard interface
The keyboard uses two I/O addresses. These are shown in Figure 10.6, and are:
•
Input/output buffer (address: 60h) - used to read the code from the keyboard.
•
Control/status register (address: 64h) - used either to determine the status of the key-
board (when a value is read from the register) or to set up the keyboard (when a value is
written to the register). The commands used are listed in Table 10.2. On a read opera-
tion, it acts as a status register. Figure 10.7 shows the bit definitions, these are:
Figure 10.6
Keyboard I/O addresses (60h and 64h)
