Atari 400 Field Service Manual

Table
1-1
Memory
Map
Selected
Lines
Signal
-Grd A15
Al*
A13
Active
Pin
-
12
13 14
15
Line
Device
L
L L
L
1-SO
8K RAM
BLOCK
L
L
L H
2 -SI
8K RAM
BLOCK
L
L H
L
3-S2
8K RAM
BLOCK
L
L H
H
*-S3
8K RAM
BLOCK
L H
L
L
5-S*
8K
RAM/CARTRIDGE
L,R
L
H
L H
6-S5
8K
RAM/CARTRIDGE
L
L
H H
L
7
-56
2K
ROM
L
H H
L
7-S6
I/O
DECODER
(Z105)
L
H
H
H
9-S7
*K ROMs
(2-"E" <Jc "A")
I/O
Decoder
The I/O
Decoder
integrated
circuit
(2105) is
a
one-of-eight
decoder
/demultiplexer.
The
I/O
Decoder
is
used
to
select
the
different
output
devices,
such
as
PIA
chip,
^^*^^y/^^P
^^
^^« ^'^*^/*^T^A
chip.
Only
four
of the
possible
output
selections
are
used.
(See
Table
1-2.)
The I/O
Decoder
Is
enabled
by
inputs
on
pins
*,
5,
and
6;
pin *
input
coming
from
the
Memory
Map
Decoder
(S6),
pin 5
input
coming
from the
Address
Bus
and
pin
6
input
coming
from
the
Chip
Select
(CS)
line.
The
Binary
Decode
is
provided
by
the
Address
Bus
(A08,
AQ9
and AlO),
ATARI
Home
Computers
1-13

Atari 400 Specifications

General

Manufacturer	Atari
Model	400
Type	Home Computer
Release Year	1979
CPU	MOS Technology 6502
CPU Speed	1.79 MHz
ROM	10 KB
Operating System	Atari OS
Keyboard	Membrane keyboard
RAM	8 KB (expandable to 48 KB)
Graphics	ANTIC and GTIA chips
Sound	4 channels
Display	RF output for connection to TV
Storage	Optional cassette tape drive or floppy disk drive
Ports	Cartridge
Display Resolution	320x192 (16 colors)