the operation of
the Terminal.
It includes
five
cursor
control
keys, a number of
keys that control
the opera-
tion of the serial
I/O,
erase
keys, and screen display
mode
keys.
It
also
includes a special character
generator
that
puts
selected
ASCII information
on
the
bus
whenever
it is required.
The
I/O board contains
latches
and
buffers to
control
parallel data transfers
between
the
Terminal
and
any
external
devices.
It also contains
the UART
(universal
asynchronous
receiver/transmitter)
that controls
se-
rial data transfers
between
the
Terminal
and any
ex-
ternal devices.
The I/O
circuit
board also
has
a special
character
detector that
monitors the
bus and looks
for
special characters such
as carriage
returns, bells, con-
trol characters, etc.
The
timing and
processing
unit
(TPU)
controls all of
the
other
functional blocks. It is the decision-making
module within the Terminal. Data
is moved.
written,
or transmitted under the control of the
TPU as a func-
tion
of the front
panel
switches
and the
data
itself. It
also
controls
cursor movements, scrolling operations,
erasing, and the
RAM
counter configurations.
The
primary
of the
power
supply consists
of slow-
blow fuse
F1, ON/OFF switch SW1, and
the dual
primary
windings
of
transformer T1. The
dual
prim-
ary windings may be
connected
in
series
for 240-volt
operation
or in
parallel
for 120-volt
operation.
The
red
secondary
winding
of the
power
transformer
supplies
g
volts
AC to the diode bridge
rectifier
D101
through D104. The rectified
output of
the
bridge
rectifier is filtered
by capacitor C1.
Integrated
circuits IC101 and ICLOZ
provide
two
regu-
lated s-volt supplies. The integrated circuits are
in-
ternally
protected
against short circuits, overloads,
and high temperature.
Capacitors
C101 and CtOz
stabilize
the regulators.
The
orange secondary
winding
supplies 28 volts
AC
to
diode
bridge rectifier
D10b
through D108.
The 36-
volt
output
of the bridge
rectifier
is filtered
by
capacitor
C2. This
36-volt
supply is one
of the outputs
of the
power
supply.
POWER
SUPPLY
VIDEO
CIRCUITS
IC103
is
a
2O-volt regulator,
but
its output
is
pro-
grammed by resistors
R103 and
R104
to supply
26
volts. ICto3 draws
its
input current
from the
base of
transistor
Q101. Q101
in turn
provides
the
larger cur-
rents
required by the
video
circuits and
regulates the
output
at
26 volts. Transistor
Q102
and
resistor
R102
limit
the short circuit
current
to
about
2 amperes.
Capacitor
C103
provides
stability
for IC103.
ICl,04
is
a
12-volt
regulator.
The input
to this
IC comes
from the
26-volt supply. Capacitor
C104
provides
sta-
bility
for IC104.
The
green
secondary
winding
supplies
15
volts AC to
diode
bridge
rectifier
D109 throughDttz.
The
DC
output
voltage
is filtered by capacitor
C105.
IC105 is a
negative,
adjustable
voltage
regulator
that
is
pro-
grammed to
-12
volts
by resistors
R105
and R106.
Capacitor
C106
provides
stability
for
IC105, while
C107
lowers
the high
frequency
output
impedance.
Resistor
R107 reduces the 15 volts AC from the
green
secondary
winding
to
provide
11
VAC
to
power
the
CRT
filament.
VERTICAL
SWEEP CIRCUITS
At the
beginning of
each
vertical scan
cycle the
verti-
cal
sync
pulse
turns on
transistor
Q301.
This
dis-
charges
the voltage
across capacitor
C303.
At the end
of the sync
pulse,
Q301
turns off.
Transistor
Q302,
a
current
source,
charges
capacitor
C303
with a con-
stant
cunent.
This
generates a linear
ramp that
is
coupled
through
resistor
R307
and capacitor C304
to
the
base of
transistor
Q303.
Transistors
Q303, Q304, Q305,
and
QgO0
form
a con-
ventional
class
B
amplifier that amplifies the ramp
to
drive the vertical
deflection
yoke.
Resistor R323
sam-
ples
the current
through the
yoke
and
provides
a
feedback voltage
through
divider
R313, R314,
and
R315 to the base
of
Q303.
Diodes D3O1 and D302
increase
the amount
of
feedback
applied at the ex-
tremes of the scan. This, in
effect,
keeps the scan
linear from
the top to the bottom
of
the
screen.
The
vertical
scan
rate
is 60.5 Hz.
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