Atari 400 Field Service Manual

Whenever the Reset key
is pressed,
the Operating
System
performs
some,
but
not
ail, of the functions
performed
at Power-Up. The
Operating
System
performs
the
following
actions after the
Reset key
is pressed:
Clears the Operating
System
portion of RAM
memory
Re-establishes
all RAM
interrupt vectors
Formats
the Handler Address
table
Initializes the ROM
Cartridges
Sets-Up the video
screen for 2* x
*0
text mode
Transfers
control
to
the ROM
Cartridge and booted
program
The remaining
2K
of Operating System ROM
is
a floating
point program which
is
not
used by
the other
parts of the Operating
System
itself, but
is available
to
non-resident
programs
such as BASIC,
Calculator, PASCAL,
etc.
The
following
routines
are among
those
found in the ROM
program;
ASCII
to
floating point
and floating
point to ASCII
conversion
Integer
to floating
point
and floating
point to integer
conversion
Floating
point log,
exponent, and
ploynomial
evaluation
Floating
point number
clear, load,
store
and move
POWER
SUPPLY
The
ifOO
and SOO Power
Supply
have
identical circuitry,
with
a few exceptions
(See
Figures 1-9
and 1-11). The
Console
Power Supplies
receive
9Vac (J20*
and J206,
i*00
and
800 respectively)
from
the external
power
adaptor (transformer)
provides +5Vdc,
and i-12Vdc,
and
-5Vdc
for the
Console. Both
the
^00
and 800
Power Supplies
have
two
power ON/OFF
switches,
S202
and S203
for the
^^00
Console,
and S201
and
S202
for the
800
Console. S202
and S201,
respectively,
are
Power
Interlock
switches.
The RF
signal
is generated
in
both the 400
and 800 Power
Supplies
from the MOD
signal
received
from the
motherboard. It
is routed
through the A203
RF Module
to
develop
the RF
output
through J203.
A
peripheral
connector
jack, 3202
for
the
*00
Console
and J204
for the 800
Console,
provides
the
serial data-in
/data-out
port for the
system. Devices
are
"daisy
chained"
together
from
this
output
port.
Each peripheral
device
is identified
by a unique
address,
enabling
all
devices
to reside
on one output
port.
Also
contained
on
the 800
Power Supply
board is the Monitor
connector
jack (3205).
Present
at
3205
are the
composite
video
signals to drive
a video monitor.
The 800
Power
Supply
board
also
contains
switches S204
thru S207. These
switches
are the
System
Reset,
Option,
Select,
and Start,
respectively.
ATARI
Home
Computers
1-16

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)