Atari 400 Field Service Manual

sent to
the
address demultiplexer, which
first
passes the lower seven
bits to
the
RAM
chips as
a
Row Address. After
an
appropriate delay,
the highest seven
bits are
passed
as a Column Address.
Data is then
either put into
or taken out
of
the
location
selected. The
direction of data flow
is determined by the Read/Write line.
REFRESH
occurs at least every
two milliseconds. The REFRESH
signal is
generated
on the
CPU
Board.
Keyboard
The
typewriter-style keyboard
is
used to generate alphanumeric
characters
as
well
as
special
graphic symbols. The
keyboard allows
the operator
to communicate with
the
console
system for writing
programs
or
responding
to preprogrammed
cassettes or
cartridges. The
keyboard
consists of 57 normally
open switches. The
switches
are
scanned at
a
rapid
rate and when
a switch
is found closed,
that scan
pattern is sent to
the Pot Keyboard
Integrated
Circuit (POKEY)
for
encoding.
Power
Supply
The
Power Supply PCB
receives 9VAC
from an external
power
adaptor (transformer)
and provides
+5Vdc,
+12Vdc,
and
-5Vdc
for the
Console
system. The Power
ON/OFF
switch is
mounted on
the Power Supply
PCB
and removes
input power
by opening the
9Vac lines.
An
interlock switch
breaks
power to
the system when
the
operator opens
the top
panel of
the Console
to install or
remove Program
Cartridges.
The RF
Module
resides
on the Power
Supply PCB,
The RF Module
generates the RF
output
for
the video
screen
from the
composite video
signals
received
from the
motherboard,
and is switchabie
to television
channel 2
or 3,
Voltages:
+5Vdc A
-
Supply
voltage
for
the logic PCBs.
t-5Vdc
B
-
Specially
filtered for
the video
circuitry,
+12Vdc
and -5Vdc
-
Supply
voltage
for the dynamic RAM
chips.
Program
Cartridge
The
Program
Cartridge
permanently
stores
the microprocessor
instructions
for
a
particular
application.
It
consists
of two
i^K
ROM
chips mounted
on the
enclosed
PCB,
Information
is
received
from the ROM
chips by addressing
the memory
locations
assigned
to the
Program
Cartridge
slot(s).
Data in the
memory locations
is then
placed
on the
Data Bus
lines.
ATARI
Home
Computers
1-6

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)