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Processor PCB
2-38
2.8
KEYBOARD
The Keyboard employs capacitance technology and an 8048, 8-bit microprocessor
that performs keyboard scanning and coding functions. It contains 109 keys in three
major groupings. The central area is a standard typewriter layout. Above the
central area are 22 user-definable function keys in a single row. To the right of the
central area are 25 keys that consist of a numeric entry pad and a set of cursor/
control keys.
As shown in Figure 2-24, the Keyboard is arranged as a matrix (8 x 16), with 128
possible
X/Y
coordinate output combinations (only 109 of which are represented
by key positions). The 8048 microprocessor, in combination with an LS74159
decoder chip, produces a scan code output function peculiar to each key position
and shift/control status. These scan codes are sent to the Processor PCB on an
eight-bit scan data bus designated SDI through SD8.
8 X 16
KEY MATRIX
Pressing a key produces a strobe that latches the corresponding scan code into a key
data register or switch (SW) register located on the Processor PCB and generates an
interrupt request. Pressing a switch key (such as FNC or SHIFT) is recorded in an
SW register on the Processor PCB, the output of which is combined with the key
data register to produce the code output.
The CPU I/O address is hexadecimal 48 for the key data register and 4C for the SW
register. The CPU can also read the keyboard status at address 4A.
Y32
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