Table of Contents
Advertisement
3-6
The
sound
carrier oscillator
and
-modulator
is
a
Colpitts-circuitry
with
transistor
309.
The
sound
carrier
frequency
can be
set
to 4.5
MHz,
5.5
MHz,
6.0
MHz
or 6.5
MHz
by means
of
corresponding
solder
links
A,
B, C.
For
6.5
MHz
all
solder
links are
open.
Adjustment
to the correct
frequency
is
achieved
by
trimmer
552, 556,
560
and
564.
The
frequency modulation of the
sound
carrier
occurs
by
varicap
410,
whereby
the deviation
for
5.5
MHz
is
adjusted
by
potmeter 692.
The
deviation of the other
sound
carrier
frequencies
depends on
tbe
capacitance
ratio.
Transistor
31
1
serves as
amplitude modulator.
The VIDEO
input
is
ac-coupled.
A
sync-separate
circuitry
(513,
614, 615,
616
and 302)
separatesa
sync-clamp-pulse
in
order
to
clamp
the
external
signal
to
ground by
transistor
303.
The
external
signal
is
buffered
by
transistor
301.
By
scaling
resistors
619
and
620
the accurate
signal level
is
added
to
tte
sound
carrier signal
to the input of signal-addition-amplifier
304/1,
2, 3,
12, 13, 14. Positive or negative
video
modulation
is
selected
by
solder
links
E
or D.
Adjustment
of the
dc-ievel
at
the
output
AM/VIDEO
in
video
mode
is
achieved
by
potmeter
631. The
residual
carrier signal
is
adjusted
by
645.
Final
amplification takes place
in
the second
signal-addition-amplifier
304/4
...
11
where
the preampli-
fied AM-signal
is
applied
via
547.
The
correct
working
point of
this
stage
is
adjusted
without any
modu-
lation
by potmeter
639. During
AM-mode
the
level
of the
RF
carrier
is
reduced
by 6
dB,
realized
by
switch
353/K
and
resistor
633.
3.4.
KEYBOARD/DISPLAY; UNIT
4.
5;
figs.
40, 41
The
central circuit
on
unit
4
is
the microprocessor
controlled
keyboard
controller
P8279.
This
interface
component
produces the
scan
signals
for
the
keyboard
matrix
and
picks
up
the return
lines,
sends
the
data
information
for
the
7-segment
displays
and
controls the multiplex
lines
for
the
display
positions.
The LED
s
INT,
AM,
FM,
VIDEO,
EXT,
REMOTE, SINGLE
and
CONT
are
driven
from
the port outputs
on
the
CPU,
unit
1
,
via
the buffers
305
and
306 on
U4.
The
information
from
the processor
is
fed to the
keyboard
controller
via
the data
bus
ADO -
AD7;
^
data
transfer
is
performed by
the
control
signals
RD,
WR,
Clk,
RES
and IRQ.
The
chip
select
signal
CS
is
generated
on
the
CPU-card from
the address
decoder
1C 320, pin
7.
Data
information
for
the
7-segment
displays
is
sent
via
the
lines
OUT
BO
- OUT
B3
to the
7-segment
decoder
1C
308 which
generates
7 output
lines
for
the segments, the decimal points
are driven
by
the
outputs
A1
and
A2
via
gate
303
or
by
the timer
circuit
1C
307
for blinking
decimal
points.
The
scan information
is
contained
in
the four
lines
SLO
—
SL3
which
are
decoded
to
Tout-of-16 with
the decoder 301.
When
the
outputs of
this circuit
are
switched
on
{=
Low)
the according
display
posi-
tion
is
lit.
Thus
the data
information
at
the
lines a-g
(7-segment) together
with
the according
set
multi-
plex
line
give
the
complete
information
for
each
display
position.
Coordination
of
the timing
between
data
information
and
multiplex
line
is
automatically
done
in
the
P8279.
Three
of the scan
lines
SLO
—
SL2
are
used
to scan the
keyboard
matrix.
The BIN
- BCD
decoder
304
produces
the information for the scan
lines
of the
keyboard-matrix, the
return
lines
are
connected
directly to 1C
302.
Pressing
one
of the keys
effects
I
RQ
(interrupt request)
be
sent to
the
main
processor
on
Unit
1
;
after this
it is
possible
to
transfer the
code
of the
key
via
the data
lines
ADO - AD7
from
the
keyboard
controller
to the
CPU
card.
The
integrated
circuit
307
is
a
timer
circuit
which
generates the
flash-clock for
the decimal points
(during
input)
or
for
the
digits in
case of
exceeding the
specifications for
the parameters. Flashing of
the decimal
points
is
enabled
by
th^puts
'FM
flash'
or
'VIDEO
flash'
being
set,
the blinking display
positions are effected
by
the
output
BD
of 1C 302.
Unit 5
contains
all
display
elements
and
switches
(keys)
and
together
with
unit
4 forms
a
sandwich
pack;
interconnections
between
themselves and connections
to the
motherboard,
unit 10, are
done
yia
CIS
connectors.
Hide quick links:
Advertisement
Table of Contents
