3. Description of function
3.01
Power
pack
(Circuit
Diagram
D)
The
power
pack
is
transforming the
power
voltage with the ferro-magnetic
constant voltage transformer
T1.
This
transformer is keeping
its
iron
core
with
a resonance
circuit
within the saturation phase,
so
that
the
voltage
changes
within permissible range of
+15%
will not influence the
secondary voltages.
At
the
power
input, a
filter
consisting of
coil
L1
and
capacitor
C1
works
against interfering frequencies.
The
primary
winding
in
the constant voltage transformer
T1
is protected
by
a thermal fuse
which
functions
at
125°C
and
a delay fuse
1.25A.
Voltage
for the secondary
circuit
is
rectified
by
the bridge
rectifiers
D1
and
D2.
The
ripple voltage generated
in
the secondary
circuit
is
smoothed
by
the capacitors
C4,
CS,
C6, C8.
High
frequency noise
is
attenuated
by
the capacitor
C7.
5V
DC
for the microcomputer
system
(UC)
is regulated
from
the
12V
(UL)
via ICI.
3.02 Switching-on routine
All
control lines outgoing
from
the
CPU
(IC4)
are set to logic
~
(+5V)
when
switching
on
the
machine
(See
3.06).
The
printer
is
moved
to the
left
until
the
arm
of reset
plate
is pulled
out of the
photo
interrupter
PH2.
After recognizing the
left
end, the
horizontal step
motor
is activated
by
the
microcomputer
so
as
to
move
the
printer
20
spacings to the
right
from
~on
the
margin
scale
(on
Pica).
This
pre-set
margin
is
programed
to set
at
20
on
the
left,
85
on
the
right
(on
Pica).
The
typewheel
is turned
by
the switching-on routine to the basic
position via
its
stepping motor.
The
ribbon step
motor
also
moves
to
its
base
position.
3.03
Keyboard,
Key
scanning
The
key
switch
modules
are mechanical contact switches
and
they close
and
open
at
the cross points of the
key
matrix
8x9
(See
circuit
Diagram
H).
When
a
key
is depressed, the contact is closed
and
effecting the
connection
between
the
columns
and
rows.
The
microprocessor
IC4
is
scanning the lines
Sp
0
...
Sp
8
and
Ze
0
...
Ze
8 every 12.6
ms
in
the
BCD
code.
Its
output pin
35
...
38
send
the scanning pulse
one
after
another to the
columns
Sp
0
...
Sp
8 via the binary decoder
IC
5
by
tapping 4 ports to
10
with H-signal
(+5V).
The
signal
scanned
forms
_I
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