vertical driver
output
pulse is applied
to
the
yoke
of
the
CRT
and
causes
vertical
deflection.
The
re
fresh
rate
is
50-60
Hz
switch
selectable.
Horizontal
Synchronization
pulses
are
applied
to
the
horizontal amplifier where
they
are amplified
and applied
to
the
horizontal driver.
The
output
of
the
horizontal drive is applied
through
the
width
coil
to
the
yoke, where it causes
the
horizontal de
flection.
The
horizontal
deflection
signal
Ts
stepped
up to approximately 12 kvwhere it is then recti
fied, filtered and applied
to
the anode cap of
the
CRT
to
provide
the
high voltage required.
Video
Information
is applied
to
the
video ampli
fier by way of
the
contrast
control, external
to
the
monitor.
The
video
information
signal
from
the video amplifier is applied
to
the
cathode
of
the
CRT gun
to
cause an ON/OFF
condition
cor
responding
to
light patterns of
the
screen. The
brightness control is external to
the
monitor
and
varies
the
voltage on
the
accelerating grid of
the
CRT.
4.2.3
Keyboard
The Keyboard is
the
input device used by
the
operator to communicate with the terminal. The
Keyboard contains
the
switches and supporting
circuitry to generate
the
appropriate control sig
nals
and
ASCII
codes
utilized
in
the
B100
Series
terminals.
The
Keyboard
conforms
to
the
pro
posed
ANSI
keyboard standard for data keys,
but
has been expanded to facilitate the capabilities
of
the
B100
Series
terminals.
The
ASCII
code
chart
is
found
in
Section
III
of
the
Operator
Manual.
The Keyboard enables
the
operator
to
manually
input information to
the
terminal. When a key
is depressed,
the
keyboard logic generates
the
corresponding 7-bit
ASCII
code and presents the
data in parallel form
to
the
keyboard data lines.
After a short delay for debouncing,
the
strobe is
driven
to
its
active
level
and
returns
after
approxi
mately 30 milliseconds. For those keys which auto-
repeat, the strobe line is pulsed at a 15 character
per second rate. The
BREAK
key is
not
encoded
but
is a
function
line
that
is driven
low
for
approxi^
mately
400
ms when
the
key is depressed. The
following keyscause special 8-bit
(non-ASCII)
4-5
codes:
AUXSEND,
CLEAR/HOM^
SEND,
EOS^
EOL,
and
DELETE
CHAR.
Thesecodes are
used
internal
to
the
CRT
only
and
are
not
trans
mitted.
424
Logic
Board
The
Logic
Board
containsthe majorfunction and
control circuits in
the
B100 Series terminal. It also
holds all of
the
DC
voltage regulators
to
power the
unit
with exception of the +5V regulator. The
basic
operations accomplished by the main
logic
board are: Generation of
data
and control signals
for
the
monitor, interaction with
the
keyboard,
control
of
the
data
sent
between
the
BlOO
terminals and any external device, and generation
of the basic timing signals essential for the oper
ation of
the
terminal. (See Figure 4-6)
Display Organization - B100/B102 —The main
timing chain (oscillator,
dot
position counter,
character position counter, character height
counter, and character linecounter) defines the
configuration of the display on the
CRT.
There
are 30
lines,
six of which are used for vertical
retrace and 24 of which are used
to
display
char
acters.
The
30
lines
are
composed
of
nine
scans
each,each scan being composed of 96 character
positions,
80 for
display
and
16
for
horizontal
re-
traca
Each character block is composed of 7 x 9
dot
matrix
field which
contains
a
5x
7
character
matrixfor the displayed character
(see
Figure44).
DisplayOrganization -
B150/B152
—The main
timing
chain
(oscillator,
dot
position
counter,
char
acter position counter, character height counter,
and character line counter) defines the configuratior
ofthe
display
on the
CRT.
There
are27
lines,
three
of which are used for vertical retrace and 24 of
which are used to display characters. The 27 lines
arecomposed of ten
scans
each, eachscan
being
composed
of 7x 10dot
matrix
field
which
contains
a 5 X7 character matrix for the displayed char
acter (see Figure 4-5).
Oscillator - The oscillator is crystal controlled
with a frequency of
10.8864
MHz.
Two
74H04'!
are connected in series by a lOOpfcapacitor.
