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Atari 400 Hardware Manual

Atari 400
113 pages
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Character
Display
Instructions:
The
first
step
in
using
the
character
map
mode
is
to
create
a
character
set
in
memory
(or
the
built-in
OS
character
set
at
hex
EOOO
may
be
used).
The
character
set
contains
eight
bytes
of
data
for
the
graphics
for
each
character.
The
meaning
of
the
data
depends
on
the
mode. The
character
set
can
contain
64
or
128
characters,
also
depending
on
the
mode. The
MSB
(Most
Significant
Byte)
of
the
address
of
the
character
set
is
stored
in
CHBASE
(or
the
OS
Shadow
CHBAS).
Only
the
most
significant
six
or
seven
bits
of
CHBAS
are
used
(see
CHBASE
description
in
section
III).
The
other
one
or
two
bits
and
the
LSB
of
the
address
are
assumed
to
be
zero,
so
the
character
set
must
start
at
an
acceptable
page
boundary.
The
next
step
is
to
set
up
the
display
list
for
the
desired
mode.
Then
the
actual
display
is
set
up.
This
consists
of
a
string
of
character
names
or
codes.
Each
name
takes
one
byte.
The
last
6
or
7
bits
of
the
name
selects
a
character.
For
a 64
character
set,
the
name
would
range
from
0
through
63
(decimal).
For
a 128
character
set,
the
range
would
be
0
through
127
(decimal).
The
upper
one
or
two
bits
of
the
name
byte
are
used
to
specify
the
color
or
other
special
information,
depending
on
the
mode.
Character
names
(codes)
are
fetched
by
the
memory
scan
counter,
and
are
placed
in
a
shift
register.
On
any
given
line
of
display
the
shift
register
rotates,
changing
only
the
name
portion
of
the
character
address,
as
shown
below.
After
a
full
line
of
character
data
has
been
displayed
the
line
counter
will
increment.
The
next
line
again
addresses
all
characters
by
name
for
that
line
number.
In
20
character
per
line
modes
the
seven
most
significant
bits
of
CHBASE
are
used.
This
requires
that
the
character
set
to
start
upon
a 512
byte
memory
boundary.
The
set
must
contain
64
charcters,
8
bytes
each,
giving
a
total
of
512
bytes
for
the
set.
The 40
character
per
line
modes
use
the
six
most
significant
bits
of
CHBASE,forcing
the
character
set
to
start
on a
1K
byte
memory
boundary.
The
set
must
have
128
characters
of
8
bytes
each.
This
gives
a
total
of
1024
bytes
for
the
set.
Hex
Graphics
Chars.
Number
Bytes
Number
Bytes
Code
Mode
Per
of
per
of
Char.
in
Line
Colors
Char.
in
set
Char
Set
2 0
40 2 8
128 1024
I
3
40 2
8 128 1024
4
40
4 8 128 1024
5
40
4
8
128 1024
6
1 20
5
8
64 512
7
2 20
5
8
64 512
II.13

Table of Contents

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Preview: Installation Instructions
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Atari 400 Specifications

General IconGeneral
ManufacturerAtari
Model400
TypeHome Computer
Release Year1979
CPUMOS Technology 6502
CPU Speed1.79 MHz
ROM10 KB
Operating SystemAtari OS
KeyboardMembrane keyboard
RAM8 KB (expandable to 48 KB)
GraphicsANTIC and GTIA chips
Sound4 channels
DisplayRF output for connection to TV
StorageOptional cassette tape drive or floppy disk drive
PortsCartridge
Display Resolution320x192 (16 colors)

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