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945424-9701
• Produces new code for each data key actuation regardless
of
any keys already being held
down.
• Makes
the
REPEAT key condition available
at
the interface.
The
keyboard has a typewriter key cluster, a numeric pad, a cursor pad, and a function key array.
Figure 1-4 illustrates
the
United States keyboard arrangement. All keys, except the REPEAT key,
are designated
as
either
mode
or
data keys.
The
mode
keys determine which eight-bit code will be
produced by each
data
key. The United States and European versions have three mode keys
(SHIFT, CONTROL, and UPPER CASE LOCK)
to
select
one
of
four codes for each data key. The
Japanese Katakana keyboard has five
mode
keys
to
select one
of
six codes for various data keys.
The
mode keys alone
do
not
cause an eight-bit code
to
be produced
by
the keyboard.
1.2.2 VIDEO DISPLAY UNIT. The video display
unit
consists
of
a
CRT
monitor
and a power/logic
pwb. The CRT
monitor
displays characters and symbols designated
by
software in
the
computer
and produced
by
the
VDT controller. The power/logic pwb provides the interface between the key-
board and
the
VDT controller; and all de
power
required by
the
keyboard,
CRT
monitor, and the
power/logic pwb. The following paragraphs describe
the
CRT
monitor
and the power/logic pwb.
1.2.2. l
CRT
Monitor. The
CRT
monitor
is a high-resolution
monitor
consisting
of
a
CRT
and a
p\vb. The pwb contains a video amplifier, a horizontal deflection amplifier, and a vertii.;al deflec-
tion amplifier. The video pwb accepts
the
video signal,
the
horizontal drive signal, and the vertical
sync signal from
the
power/logic
pwb;
and provides
the
signal shaping necessary
to
display
the
character designated
by
the
data
portion
of
the
video signal on
the
CRT
screen.
Video data, horizontal drive, and vertical sync are separated
out
of
the
composite video signal by
the
circuitry
on
the
power/logic pwb and amplified separately. The horizontal drive
component
is
provided
to
the
logic in
the
keyboard
data
path
to
provide timing for
data
transfers.
The
CRT
monitor
is
capable
of
displaying 12
or
24 rows (as directed by
the
VDT controller)
of
80
characters each. Characters are normally displayed
on
a dark background except
at
the cursor
position. The cursor
is
displayed in reverse video format. (Reverse video format implies displaying
a lighted background surrounding a dark character.)
The cursor appears
on
the
CRT
screen
as
a steady
or
blinking (software selected) high-intensity
character block where
the
next
character
or
symbol
is
to
be entered.
If
the
cursor
is
positioned
over a displayed character, the character
is
displayed in reverse video format.
If
software directs
cursor blinking,
the
cursor and character
at
that
position blink in complementary video formats.
All information displayed
on
the
CRT
screen is originated
by
software executing in the computer.
The actual video signals for displaying information
on
the screen are generated by character gen-
eration read-only memories (ROMs)
on
the VDT controller.
1.2.2.2 Power/Logic
PWB.
The power/logic pwb contains logic
that
provides the interfaces
between the keyboard and
the
VDT controller and between the VDT controller and the CRT
monitor. The power/logic pwb also contains three power supply circuits
that
provide
+5
Vdc
to
the
keyboard, and -12 Vdc and +
15
Vdc
to
the
keyboard and video data
path
logic
on
the pwb
and
the
CRT monitor.
Digital
Systems Division
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