REV.-A
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Sub-CPU
Main
CPU
1
1-
7508
GAH40M
Z-80
1
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SET
RESET
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READY
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LED
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(Keyboard)
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Fig.
2-64
Keyboard
Input
Operation
Block
Diagram
The keyboard keys are scanned
by
the sub-CPU
which
controls
the
key data
outputs
as
follows:
(1) Key
switch
(CTRL, SHIFT(R), SHIFT(L), CAPS LOCK,
NUM
GRPH, and CTRL (right
of
the
space-
bar)
output
control
When
any
of
these keys is pressed
for
the
first
time
(i.e.,
it
is stet),
the
sub-CPU issues a
MAKE code.
When
it
is pressed
for
the
second
time
(i.e.,
it
is released),
the
sub-CPU issues a
BREAK code. This is required
for
the
correct keyboard data input, because the keyboard
input
mode is controlled
by
these keys and
the
main
CPU
has
to
be informed
whether
anyone
of
them
is in effect. Fig.
2-65
illustrates a sample sequence
of
key strokes,
which
includes
shift
operations in
the
alphanumeric mode: The sub-CPU issues
the
MAKE and BREAK codes
for
the
left SHFT key
when
it
is locked and released respectively. The main
CPU
can display
the
intended upper case and
lower
case alphabets
as
shown
below.
Character data keys
Function key
(left SHIFT)
Key codes output
from
7508
Characters displayed
by main
CPU
Fig.
2-65
Keyboard
Data
Input
And
Mode
Control
Sample
2-65
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