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945424-9701
Keyboard
and
Video Data Path Logic. The keyboard and video data path logic on the
power/logic pwb performs the following functions:
• Latches keyboard data from the keyboard and holds the last code entered from the
keyboard until a new code
is
entered
• Adds one start bit, one stop bit, and one parity bit
to
the keyboard data code
• Serializes the keyboard data ·code and transmits the serial code to the VDT controller
• Converts
the
serial keyboard data into an eight-bit parallel code and a parity error
indicator bit and displays the bits with nine light-emitting diodes (LEDs) on the rear
of
the display unit housing
• Repeatedly produces the 11-bit serial code for any data key actuated with the REPEAT
key held
• Produces an audio signal
to
drive a loudspeaker in the display unit cabinet in response
to a software-produced alarm condition
• Provides amplifier for monitoring audio signals from a modem.
• Buffers composite video signal from VDT controller before providing the signal to
other
circuitry
• Separates video, horizontal drive, and vertical synchronization components from
the
composite video signal from VDT controller
• Provides video data, horizontal drive, and vertical synchronization signals
to
drive CRT
monitor circuitry
• Compensates for cable lengths shorter
or
longer than approximately 1000 feet
(304.8 metres) with a switch-selectable-gain video amplifier
that
provides its low gain
for short cables and its high gain for long cables.
Power Supplies. There are three series-regulated de power supply circuits on the power/logic
pwb. These supplies are provided with alternating current (ac)
by
a multiple-secondary power
transformer mounted in the base
of
the display unit cabinet. The power supplies provide
+5
V de
to
the keyboard, and -12 V de and +
15
V de
to
the CRT monitor's video pwb, keyboard, and
video data path logic on the power/logic pwb.
1.2.3 VDT CONTROLLER. The VDT controller
is
implemented on a pwb
that
occupies a full
slot in either a main
or
expansion
computer
chassis. The pwb contains the logic for one (always)
or
two (optionally) autonomous controllers, and supports
as
many keyboard/display unit com-
binations
as
there are controllers on the pwb. When two controllers reside on a single pwb, the
controllers share the same CRU interface and time-base generator.
In this manual, the discussion concerns itself with the primary controller
that
is
always present.
The discussion
is
valid for the second controller,
if
present. On the logic diagrams for the VDT
controller, logic for two controllers
is
included with signatures for the second controller denoted
by
an asterisk(*)
as
the last character
of
each signature.
1-7
Digital
Systems Division
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