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RAM
(IC16
-
IC19)
provides storage
for the
programs and/or data
currently being executed.
In the
standard
unit,
these
four ICs are 64K
x
4
but
may
be
upgraded
to
sixteen
256K
x
1
ICs as an
option. (See
Paragraph
3.3 on
page
28
for
instructions.)
In
addition, the same
RAM
is
used
to
generate
the
video
display. Normally, no conflict will
be
observed because
the
program will
use one portion of
RAM and
the
display will use another. During
normal usage, the BASIC interpreter,
located
in
ROM, will control the
execution
of
programs located
in RAM.
A central component
in
the
Color
Computer
3
is
the
Advanced Color
Video Chip
(IC6). This chip
provides
refresh and address multiplexing
for
the RAM,
It
also provides all of
the
system timing and device selection.
ACVC comprises
the
VDG (Video Display
Generator) function which supports
High-Resolution
mode,
in
addition
to
all other
modes included
in
the
Color
Computer
2.
During High-Resolution
mode,
it
generates
40 x 24 or 80 x 24
text screen, and 320
x
192 or 640
x
192
graphics
screen.
It
is
also
designed
to
output
two
different
video signals
-
composite video
and
analog RGB.
ACVC can expand memory space
up to
512K bytes. Having
a
built-in MMU
(Memory Management Unit),
it
can
support
2
banks of 256K-byte
RAM,
each with
a
9-line address
bus,
even
though the CPU possesses only
16
address
lines.
The
remaining circuitry
in the
Color
Computer
3
is
devoted
to
Input/Output
(I/O)
communication. The most
important part
of this
circuitry
is
the
keyboard, which allows
the
operator
to
enter information. Other
I/O circuits are provided
to
allow
joystick
input,
cassette
input and
output, and RS-232C input
and
output.
-6-
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