Radio Shack CCR-81 Technical Reference Manual

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SYN
:
FIGURE
9. VIDEO INPUT
TO THE
MODULATOR
The
UM1
285-8
modulator
is
a high
performance
intercarrier
vestigial
sideband
unit.
The
modulator
is
powered
off the
12-
volt supply
with
an inline
current
limiting
resistor,
R45. The
modulator
also
has sound
capability
which
is used by
the
Color
Computer.
The last
input
to the modulator
is the
channel
select switch
(S3). Channel
4 is
selected by
allowing
the
input
to
float high.
Channel
3 is selected
by
ground.
PIA's
The
Color
Computer
uses
two peripheral
interface
adapters
(PIA's).
These
devices
provide
a universal
interface
to the
6809E CPU
chip,
and they
support
all of the
I/O functions in
the
Color
Computer.
The functional
configuration
of the PIA is programmed
by the
CPU during
the reset routine.
Each of the peripheral
data lines
may be
programmed to
act as an input or
output, and each of
four
control/interrupt
lines may be programmed
for one of
several
control modes.
Figure
10
shows
a block diagram of
a
PIA.
Internal
to
the modulator,
the
DC sound input
signal
is
converted
to
a 4.5 MHz
frequency
modulated
signal.
This
signal
is then mixed
with
the video
and used
to modulate
the
RF
signal for
the selected
channel
(61.25 MHz for
Channel
3
or
67.25
MHz for
channel
4). This final
output
is
available
at
the
phone
jack
connector
of the
modulator.
As shown in the block
diagram,
a PIA consists of two
8-bit
data registers
and
4 control/interrupt
lines. The two 8-bit
data
registers
are controlled
by two data direction
registers.
These
direction
control registers
are set up by the
reset routine and
normally will
not be changed.
40
CA1
39
CA2
CSfl 22
CS1
24
CS2* 23
RS0 36
RS1
35
R/W 21
Enable 25
Reset* 34
—
Chip Seiect
and
R/W
Control
19
CB2
FIGURE
10. PIA
BLOCK
DIAGRAM
29

Radio Shack CCR-81 Specifications

General

Brand	Radio Shack
Model	CCR-81
Category	Desktop
Language	English